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  • 1.
    Abbas, Zainab
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Al-Shishtawy, Ahmad
    RISE SICS, Stockholm, Sweden.
    Girdzijauskas, Sarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS, Stockholm, Sweden..
    Vlassov, Vladimir
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Short-Term Traffic Prediction Using Long Short-Term Memory Neural Networks2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Short-term traffic prediction allows Intelligent Transport Systems to proactively respond to events before they happen. With the rapid increase in the amount, quality, and detail of traffic data, new techniques are required that can exploit the information in the data in order to provide better results while being able to scale and cope with increasing amounts of data and growing cities. We propose and compare three models for short-term road traffic density prediction based on Long Short-Term Memory (LSTM) neural networks. We have trained the models using real traffic data collected by Motorway Control System in Stockholm that monitors highways and collects flow and speed data per lane every minute from radar sensors. In order to deal with the challenge of scale and to improve prediction accuracy, we propose to partition the road network into road stretches and junctions, and to model each of the partitions with one or more LSTM neural networks. Our evaluation results show that partitioning of roads improves the prediction accuracy by reducing the root mean square error by the factor of 5. We show that we can reduce the complexity of LSTM network by limiting the number of input sensors, on average to 35% of the original number, without compromising the prediction accuracy.

  • 2.
    Abbas, Zainab
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Kalavri, Vasiliki
    Systems Group, ETH, Zurich, Switzerland.
    Carbone, Paris
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Vlassov, Vladimir
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Streaming Graph Partitioning: An Experimental Study2018Inngår i: Proceedings of the VLDB Endowment, ISSN 2150-8097, E-ISSN 2150-8097, Vol. 11, nr 11, s. 1590-1603Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graph partitioning is an essential yet challenging task for massive graph analysis in distributed computing. Common graph partitioning methods scan the complete graph to obtain structural characteristics offline, before partitioning. However, the emerging need for low-latency, continuous graph analysis led to the development of online partitioning methods. Online methods ingest edges or vertices as a stream, making partitioning decisions on the fly based on partial knowledge of the graph. Prior studies have compared offline graph partitioning techniques across different systems. Yet, little effort has been put into investigating the characteristics of online graph partitioning strategies.

    In this work, we describe and categorize online graph partitioning techniques based on their assumptions, objectives and costs. Furthermore, we employ an experimental comparison across different applications and datasets, using a unified distributed runtime based on Apache Flink. Our experimental results showcase that model-dependent online partitioning techniques such as low-cut algorithms offer better performance for communication-intensive applications such as bulk synchronous iterative algorithms, albeit higher partitioning costs. Otherwise, model-agnostic techniques trade off data locality for lower partitioning costs and balanced workloads which is beneficial when executing data-parallel single-pass graph algorithms.

  • 3.
    Abbas, Zainab
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Sigurdsson, Thorsteinn Thorri
    KTH.
    Al-Shishtawy, Ahmad
    RISE Res Inst Sweden, Stockholm, Sweden..
    Vlassov, Vladimir
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Evaluation of the Use of Streaming Graph Processing Algorithms for Road Congestion Detection2018Inngår i: 2018 IEEE INT CONF ON PARALLEL & DISTRIBUTED PROCESSING WITH APPLICATIONS, UBIQUITOUS COMPUTING & COMMUNICATIONS, BIG DATA & CLOUD COMPUTING, SOCIAL COMPUTING & NETWORKING, SUSTAINABLE COMPUTING & COMMUNICATIONS / [ed] Chen, JJ Yang, LT, IEEE COMPUTER SOC , 2018, s. 1017-1025Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Real-time road congestion detection allows improving traffic safety and route planning. In this work, we propose to use streaming graph processing algorithms for road congestion detection and evaluate their accuracy and performance. We represent road infrastructure sensors in the form of a directed weighted graph and adapt the Connected Components algorithm and some existing graph processing algorithms, originally used for community detection in social network graphs, for the task of road congestion detection. In our approach, we detect Connected Components or communities of sensors with similarly weighted edges that reflect different states in the traffic, e.g., free flow or congested state, in regions covered by detected sensor groups. We have adapted and implemented the Connected Components and community detection algorithms for detecting groups in the weighted sensor graphs in batch and streaming manner. We evaluate our approach by building and processing the road infrastructure sensor graph for Stockholm's highways using real-world data from the Motorway Control System operated by the Swedish traffic authority. Our results indicate that the Connected Components and DenGraph community detection algorithms can detect congestion with accuracy up to approximate to 94% for Connected Components and up to approximate to 88% for DenGraph. The Louvain Modularity algorithm for community detection fails to detect congestion regions for sparsely connected graphs, representing roads that we have considered in this study. The Hierarchical Clustering algorithm using speed and density readings is able to detect congestion without details, such as shockwaves.

  • 4.
    Alferez, Mauricio
    et al.
    Univ Luxembourg, Interdisciplinary Ctr Secur Reliabil & Trust SnT, 2 Ave JF Kennedy, L-1855 Luxembourg, Luxembourg..
    Acher, Mathieu
    Univ Rennes, DiverSE Team Inria Rennes, IRISA, CNRS, Rennes, France..
    Galindo, Jose A.
    Univ Seville, Dept Comp Languages & Syst, Seville, Spain..
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Benavides, David
    Univ Seville, Dept Comp Languages & Syst, Seville, Spain..
    Modeling variability in the video domain: language and experience report2019Inngår i: Software quality journal, ISSN 0963-9314, E-ISSN 1573-1367, Vol. 27, nr 1, s. 307-347Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an industrial project, we addressed the challenge of developing a software-based video generator such that consumers and providers of video processing algorithms can benchmark them on a wide range of video variants. This article aims to report on our positive experience in modeling, controlling, and implementing software variability in the video domain. We describe how we have designed and developed a variability modeling language, called VM, resulting from the close collaboration with industrial partners during 2 years. We expose the specific requirements and advanced variability constructs; we developed and used to characterize and derive variations of video sequences. The results of our experiments and industrial experience show that our solution is effective to model complex variability information and supports the synthesis of hundreds of realistic video variants. From the software language perspective, we learned that basic variability mechanisms are useful but not enough; attributes and multi-features are of prior importance; meta-information and specific constructs are relevant for scalable and purposeful reasoning over variability models. From the video domain and software perspective, we report on the practical benefits of a variability approach. With more automation and control, practitioners can now envision benchmarking video algorithms over large, diverse, controlled, yet realistic datasets (videos that mimic real recorded videos)-something impossible at the beginning of the project.

  • 5.
    Apolonia, Nuno
    et al.
    Universitat Politecnica de Catalunya (UPC) Barcelona, Spain.
    Antaris, Stefanos
    Girdzijauskas, Šarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Pallis, G.
    Dikaiakos, Marios
    SELECT: A distributed publish/subscribe notification system for online social networks2018Inngår i: Proceedings - 2018 IEEE 32nd International Parallel and Distributed Processing Symposium, IPDPS 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 970-979, artikkel-id 8425250Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Publish/subscribe (pub/sub) mechanisms constitutean attractive communication paradigm in the design of large-scale notification systems for Online Social Networks (OSNs). Toaccommodate the large-scale workloads of notifications producedby OSNs, pub/sub mechanisms require thousands of serversdistributed on different data centers all over the world, incurringlarge overheads. To eliminate the pub/sub resources used, wepropose SELECT - a distributed pub/sub social notificationsystem over peer-to-peer (P2P) networks. SELECT organizesthe peers on a ring topology and provides an adaptive P2Pconnection establishment algorithm where each peer identifiesthe number of connections required, based on the social structureand user availability. This allows to propagate messages to thesocial friends of the users using a reduced number of hops.The presented algorithm is an efficient heuristic to an NP-hard problem which maps workload graphs to structured P2Poverlays inducing overall, close to theoretical, minimal number ofmessages. Experiments show that SELECT reduces the numberof relay nodes up to 89% versus the state-of-the-art pub/subnotification systems. Additionally, we demonstrate the advantageof SELECT against socially-aware P2P overlay networks andshow that the communication between two socially connectedpeers is reduced on average by at least 64% hops, while achieving100% communication availability even under high churn.

  • 6.
    Apolonia, Nuno
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT). Universitat Politecnica de Catalunya (UPC) Barcelona, Spain.
    Freitag, Felix
    Universitat Politècnica de Catalunya. Barcelona, Spain.
    Navarro, Leandro
    Universitat Politècnica de Catalunya, BarcelonaTECH, Barcelona, Spain.
    Girdzijauskas, Sarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Socially aware microcloud service overlay optimization in community networks2019Inngår i: Software, practice & experience, ISSN 0038-0644, Vol. 49, nr 1, artikkel-id 13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Community networks are a growing network cooperation effort by citizens to build and maintain Internet infrastructure in regions that are not available. Adding that, to bring cloud services to community networks (CNs), microclouds were started as an edge cloud computing model where members cooperate using resources. Therefore, enhancing routing for services in CNs is an attractive paradigm that benefits the infrastructure. The problem is the growing consumption of resources for disseminating messages in the CN environment. This is because the services that build their overlay networks are oblivious to the underlying workload patterns that arise from social cooperation in CNs. In this paper, we propose Select in Community Networks (SELECTinCN), which enhances the overlay creation for pub/sub systems over peer‐to‐peer (P2P) networks. Moreover, SELECTinCN includes social information based on cooperation within CNs by exploiting the social aspects of the community of practice. Our work organizes the peers in a ring topology and provides an adaptive P2P connection establishment algorithm, where each peer identifies the number of connections needed based on the social structure and user availability. This allows us to propagate messages using a reduced number of hops, thus providing an efficient heuristic to an NP‐hard problem that maps the workload graph to the structured P2P overlays resulting in a number of messages close to the theoretical minimum. Experiments show that, by using social network information, SELECTinCN reduces the number of relay nodes by up to 89% using the community of practice information versus the state‐of‐the‐art pub/sub notification systems given as baseline.

  • 7.
    Bahri, Leila
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Carminati, Barbara
    Ferrari, Elena
    Univ Insubria, Dept Theoret & Appl Sci, Varese, Italy..
    Knowledge-based approaches for identity management in online social networks2018Inngår i: WILEY INTERDISCIPLINARY REVIEWS-DATA MINING AND KNOWLEDGE DISCOVERY, ISSN 1942-4787, Vol. 8, nr 5, artikkel-id e1260Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    When we meet a new person, we start by introducing ourselves. We share our names, and other information about our jobs, cities, family status, and so on. This is how socializing and social interactions can start: we first need to identify each other. Identification is a cornerstone in establishing social contacts. We identify ourselves and others by a set of civil (e.g., name, nationality, ID number, gender) and social (e.g., music taste, hobbies, religion) characteristics. This seamlessly carried out identification process in face-to-face interactions is challenged in the virtual realms of socializing, such as in online social network (OSN) platforms. New identities (i.e., online profiles) could be created without being subject to any level of verification, making it easy to create fake information and forge fake identities. This has led to a massive proliferation of accounts that represent fake identities (i.e., not mapping to physically existing entities), and that poison the online socializing environment with fake information and malicious behavior (e.g., child abuse, information stealing). Within this milieu, users in OSNs are left unarmed against the challenging task of identifying the real person behind the screen. OSN providers and research bodies have dedicated considerable effort to the study of the behavior and features of fake OSN identities, trying to find ways to detect them. Some other research initiatives have explored possible techniques to enable identity validation in OSNs. Both kinds of approach rely on extracting knowledge from the OSN, and exploiting it to achieve identification management in their realms. We provide a review of the most prominent works in the literature. We define the problem, provide a taxonomy of related attacks, and discuss the available solutions and approaches for knowledge-based identity management in OSNs. This article is categorized under: Fundamental Concepts of Data and Knowledge > Human Centricity and User Interaction Application Areas> Internet and Web-Based Applications Application Areas> Society and Culture

  • 8.
    Bahri, Leila
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Girdzijauskas, Sarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Blockchain technology: Practical P2P computing (Tutorial)2019Inngår i: Proceedings - 2019 IEEE 4th International Workshops on Foundations and Applications of Self* Systems, FAS*W 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 249-250, artikkel-id 8791982Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Blockchain technology comes with the promise to revolutionize the way current IT systems are organized as well as to revise how trust is perceived in the wider society. In spite of the wide attention that cyrpto-currencies (such as Bitcoin) have attracted, Blockchain technology is more likely to make an impact beyond ongoing speculations on cyrpto-currencies. Decentralized identity management, transparent supply-chain systems, and IoT governance and security are only few examples of research challenges for which this technology may hold substantial potential. Blockchain technology has emerged at the intersection of two well established research areas: peer-to-peer (P2P) computing and cryptography. In this tutorial, we provide a general overview of the main components behind this technology, we present the difference between the types of Blockchain available today, and we make a high level discussion on its potentials and limitations as well as possible research challenges.

  • 9.
    Bahri, Leila
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Girdzijauskas, Sarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Trust Mends Blockchains: Living up to Expectations2019Inngår i: IEEE 39th International Conference on Distributed Computing Systems (ICDCS), Dallas, July 7-10 2019, 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    At the heart of Blockchains is the trustless leader election mechanism for achieving consensus among pseudoanonymous peers, without the need of oversight from any third party or authority whatsoever. So far, two main mechanisms are being discussed: proof-of-work (PoW) and proof-of-stake (PoS). PoW relies on demonstration of computational power, and comes with the markup of huge energy wastage in return of the stake in cyrpto-currency. PoS tries to address this by relying on owned stake (i.e., amount of crypto-currency) in the system. In both cases, Blockchains are limited to systems with financial basis. This forces non-crypto-currency Blockchain applications to resort to “permissioned” setting only, effectively centralizing the system. However, non-crypto-currency permisionless blockhains could enable secure and self-governed peer-to-peer structures for numerous emerging application domains, such as education and health, where some trust exists among peers. This creates a new possibility for valuing trust among peers and capitalizing it as the basis (stake) for reaching consensus. In this paper we show that there is a viable way for permisionless non-financial Blockhains to operate in completely decentralized environments and achieve leader election through proof-of-trust (PoT). In our PoT construction, peer trust is extracted from a trust network that emerges in a decentralized manner and is used as a waiver for the effort to be spent for PoW, thus dramatically reducing total energy expenditure of the system. Furthermore, our PoT construction is resilient to the risk of small cartels monopolizing the network (as it happens with the mining-pool phenomena in PoW) and is not vulnerable to sybils. We evluate security guarantees, and perform experimental evaluation of our construction, demonstrating up to 10-fold energy savings compared to PoW without trading off any of the decentralization characteristics, with further guarantees against risks of monopolization.

  • 10.
    Bahri, Leila
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Girdzijauskas, Sarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    When Trust Saves Energy - A Reference Framework for Proof-of-Trust (PoT) Blockchains2018Inngår i: WWW '18 Companion Proceedings of the The Web Conference 2018, ACM Digital Library, 2018, s. 1165-1169Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Blockchains are attracting the attention of many technical, financial, and industrial parties, as a promising infrastructure for achieving secure peer-to-peer (P2P) transactional systems. At the heart of blockchains is proof-of-work (PoW), a trustless leader election mechanism based on demonstration of computational power. PoW provides blockchain security in trusless P2P environments, but comes at the expense of wasting huge amounts of energy. In this research work, we question this energy expenditure of PoW under blockchain use cases where some form of trust exists between the peers. We propose a Proof-of-Trust (PoT) blockchain where peer trust is valuated in the network based on a trust graph that emerges in a decentralized fashion and that is encoded in and managed by the blockchain itself. This trust is then used as a waiver for the difficulty of PoW; that is, the more trust you prove in the network, the less work you do.

  • 11.
    Baudry, Benoit
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Harrand, Nicolas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Schulte, E.
    Timperley, C.
    Tan, S. H.
    Selakovic, M.
    Ugherughe, E.
    A spoonful of DevOps helps the GI go down2018Inngår i: Proceedings - International Conference on Software Engineering, IEEE Computer Society , 2018, s. 35-36Konferansepaper (Fagfellevurdert)
    Abstract [en]

    DevOps emphasizes a high degree of automation at all phases of the software development lifecyle. Meanwhile, Genetic Improvement (GI) focuses on the automatic improvement of software artifacts. In this paper, we discuss why we believe that DevOps offers an excellent technical context for easing the adoption of GI techniques by software developers. We also discuss A/B testing as a prominent and clear example of GI taking place in the wild today, albeit one with human-supervised fitness and mutation operators.

  • 12.
    Boman, Magnus
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    ben Abdesslem, Fehmi
    Forsell, Erik
    Gillblad, Daniel
    Görnerup, Olof
    Isacsson, Nils
    Sahlgren, Magnus
    Kaldo, Viktor
    Learning machines in Internet-delivered psychological treatment2019Inngår i: Progress in artificial intelligenceArtikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Boman, Magnus
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Heger, Tobias
    Circles of Impression: External Foresight in Global Enterprises2019Inngår i: Futures Thinking and Organizational Policy / [ed] D. A. Schreiber and Z. L. Berge, Cham: Palgrave Macmillan, 2019, s. 179-199Kapittel i bok, del av antologi (Fagfellevurdert)
  • 14.
    Borlenghi, Simone
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Boman, Magnus
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS, Electrum 229, SE-16429 Kista, Sweden..
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Modeling reservoir computing with the discrete nonlinear Schrodinger equation2018Inngår i: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, nr 5, artikkel-id 052101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrodinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 15. Bousse, Erwan
    et al.
    Leroy, Dorian
    Combemale, Benoit
    Wimmer, Manuel
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Omniscient debugging for executable DSLs2018Inngår i: Journal of Systems and Software, ISSN 0164-1212, E-ISSN 1873-1228, Vol. 137, s. 261-288Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Omniscient debugging is a promising technique that relies on execution traces to enable free traversal of the states reached by a model (or program) during an execution. While a few General-Purpose Languages (GPLs) already have support for omniscient debugging, developing such a complex tool for any executable Domain Specific Language (DSL) remains a challenging and error prone task. A generic solution must: support a wide range of executable DSLs independently of the metaprogramming approaches used for implementing their semantics; be efficient for good responsiveness. Our contribution relies on a generic omniscient debugger supported by efficient generic trace management facilities. To support a wide range of executable DSLs, the debugger provides a common set of debugging facilities, and is based on a pattern to define runtime services independently of metaprogramming approaches. Results show that our debugger can be used with various executable DSLs implemented with different metaprogramming approaches. As compared to a solution that copies the model at each step, it is on average sixtimes more efficient in memory, and at least 2.2 faster when exploring past execution states, while only slowing down the execution 1.6 times on average.

  • 16.
    Broman, David
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Hybrid Simulation Safety: Limbos and Zero Crossings2018Inngår i: Principles of Modeling: Essays Dedicated to Edward A. Lee on the Occasion of His 60th Birthday, Springer, 2018, s. 106-121Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Physical systems can be naturally modeled by combining continuous and discrete models. Such hybrid models may simplify the modeling task of complex system, as well as increase simulation performance. Moreover, modern simulation engines can often efficiently generate simulation traces, but how do we know that the simulation results are correct? If we detect an error, is the error in the model or in the simulation itself? This paper discusses the problem of simulation safety, with the focus on hybrid modeling and simulation. In particular, two key aspects are studied: safe zero-crossing detection and deterministic hybrid event handling. The problems and solutions are discussed and partially implemented in Modelica and Ptolemy II.

  • 17.
    Broman, David
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Siek, J. G.
    United States.
    Gradually typed symbolic expressions2017Inngår i: PEPM 2018 - Proceedings of the ACM SIGPLAN Workshop on Partial Evaluation and Program Manipulation, Co-located with POPL 2018, Association for Computing Machinery (ACM), 2017, s. 15-29Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Embedding a domain-specific language (DSL) in a general purpose host language is an efficient way to develop a new DSL. Various kinds of languages and paradigms can be used as host languages, including object-oriented, functional, statically typed, and dynamically typed variants, all having their pros and cons. For deep embedding, statically typed languages enable early checking and potentially good DSL error messages, instead of reporting runtime errors. Dynamically typed languages, on the other hand, enable flexible transformations, thus avoiding extensive boilerplate code. In this paper, we introduce the concept of gradually typed symbolic expressions that mix static and dynamic typing for symbolic data. The key idea is to combine the strengths of dynamic and static typing in the context of deep embedding of DSLs. We define a gradually typed calculus <*>, formalize its type system and dynamic semantics, and prove type safety. We introduce a host language called Modelyze that is based on <*>, and evaluate the approach by embedding a series of equation-based domain-specific modeling languages, all within the domain of physical modeling and simulation.

  • 18.
    Cabrera Arteaga, Javier
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teoretisk datalogi, TCS.
    Monperrus, Martin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teoretisk datalogi, TCS.
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Scalable comparison of JavaScript V8 bytecode traces2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The comparison and alignment of runtime traces are essential, e.g., for semantic analysis or debugging. However, naive sequence alignment algorithms cannot address the needs of the modern web: (i) the bytecode generation process of V8 is not deterministic; (ii) bytecode traces are large.

    We present STRAC, a scalable and extensible tool tailored to compare bytecode traces generated by the V8 JavaScript engine. Given two V8 bytecode traces and a distance function between trace events, STRAC computes and provides the best alignment. The key insight is to split access between memory and disk. STRAC can identify semantically equivalent web pages and is capable of processing huge V8 bytecode traces whose order of magnitude matches today's web like https://2019.splashcon.org, which generates approx. 150k of V8 bytecode instructions.

  • 19.
    Carbone, Paris
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Scalable and Reliable Data Stream Processing2018Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Data-stream management systems have for long been considered as a promising architecture for fast data management. The stream processing paradigm poses an attractive means of declaring persistent application logic coupled with state over evolving data. However, despite contributions in programming semantics addressing certain aspects of data streaming, existing approaches have been lacking a clear, universal specification for the underlying system execution. We investigate the case of data stream processing as a general-purpose scalable computing architecture that can support continuous and iterative state-driven workloads. Furthermore, we examine how this architecture can enable the composition of reliable, reconfigurable services and complex applications that go even beyond the needs of scalable data analytics, a major trend in the past decade.

    In this dissertation, we specify a set of core components and mechanisms to compose reliable data stream processing systems while adopting three crucial design principles: blocking-coordination avoidance, programming-model transparency, and compositionality. Furthermore, we identify the core open challenges among the academic and industrial state of the art and provide a complete solution using these design principles as a guide. Our contributions address the following problems: I) Reliable Execution and Stream State Management, II) Computation Sharing and Semantics for Stream Windows, and III) Iterative Data Streaming. Several parts of this work have been integrated into Apache Flink, a widely-used, open-source scalable computing framework, and supported the deployment of hundreds of long-running large-scale production pipelines worldwide.

  • 20.
    Castañeda Lozano, Roberto
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS (Swedish Institute of Computer Science).
    Constraint-Based Register Allocation and Instruction Scheduling2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to improve latency or throughput) are central compiler problems. This dissertation proposes a combinatorial optimization approach to these problems that delivers optimal solutions according to a model, captures trade-offs between conflicting decisions, accommodates processor-specific features, and handles different optimization criteria.

    The use of constraint programming and a novel program representation enables a compact model of register allocation and instruction scheduling. The model captures the complete set of global register allocation subproblems (spilling, assignment, live range splitting, coalescing, load-store optimization, multi-allocation, register packing, and rematerialization) as well as additional subproblems that handle processor-specific features beyond the usual scope of conventional compilers.

    The approach is implemented in Unison, an open-source tool used in industry and research that complements the state-of-the-art LLVM compiler. Unison applies general and problem-specific constraint solving methods to scale to medium-sized functions, solving functions of up to 647 instructions optimally and improving functions of up to 874 instructions. The approach is evaluated experimentally using different processors (Hexagon, ARM and MIPS), benchmark suites (MediaBench and SPEC CPU2006), and optimization criteria (speed and code size reduction). The results show that Unison generates code of slightly to significantly better quality than LLVM, depending on the characteristics of the targeted processor (1% to 9.3% mean estimated speedup; 0.8% to 3.9% mean code size reduction). Additional experiments for Hexagon show that its estimated speedup has a strong monotonic relationship to the actual execution speedup, resulting in a mean speedup of 5.4% across MediaBench applications.

    The approach contributed by this dissertation is the first of its kind that is practical (it captures the complete set of subproblems, scales to medium-sized functions, and generates executable code) and effective (it generates better code than the LLVM compiler, fulfilling the promise of combinatorial optimization). It can be applied to trade compilation time for code quality beyond the usual optimization levels, explore and exploit processor-specific features, and identify improvement opportunities in conventional compilers.

  • 21.
    Castañeda Lozano, Roberto
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS, Electrum 229, Kista, 164 40, Sweden.
    Carlsson, M.
    Hjort Blindell, Gabriel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Schulte, Christian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS, Electrum 229, Kista, 164 40, Sweden.
    Combinatorial register allocation and instruction scheduling2019Inngår i: ACM Transactions on Programming Languages and Systems, ISSN 0164-0925, E-ISSN 1558-4593, Vol. 41, nr 3, artikkel-id 17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article introduces a combinatorial optimization approach to register allocation and instruction scheduling, two central compiler problems. Combinatorial optimization has the potential to solve these problems optimally and to exploit processor-specific features readily. Our approach is the first to leverage this potential in practice: it captures the complete set of program transformations used in state-of-the-art compilers, scales to medium-sized functions of up to 1,000 instructions, and generates executable code. This level of practicality is reached by using constraint programming, a particularly suitable combinatorial optimization technique. Unison, the implementation of our approach, is open source, used in industry, and integrated with the LLVM toolchain. An extensive evaluation confirms that Unison generates better code than LLVM while scaling to medium-sized functions. The evaluation uses systematically selected benchmarks from MediaBench and SPEC CPU2006 and different processor architectures (Hexagon, ARM, MIPS). Mean estimated speedup ranges from 1.1% to 10% and mean code size reduction ranges from 1.3% to 3.8% for the different architectures. A significant part of this improvement is due to the integrated nature of the approach. Executing the generated code on Hexagon confirms that the estimated speedup results in actual speedup. Given a fixed time limit, Unison solves optimally functions of up to 946 instructions, nearly an order of magnitude larger than previous approaches. The results show that our combinatorial approach can be applied in practice to trade compilation time for code quality beyond the usual compiler optimization levels, identify improvement opportunities in heuristic algorithms, and fully exploit processor-specific features.

  • 22.
    Castañeda Lozano, Roberto
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS (Swedish Institute of Computer Science).
    Carlsson, Mats
    RISE SICS (Swedish Institute of Computer Science).
    Hjort Blindell, Gabriel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Schulte, Christian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Combinatorial Register Allocation and Instruction Scheduling2018Rapport (Annet vitenskapelig)
    Abstract [en]

    This paper introduces a combinatorial optimization approach to register allocation and instruction scheduling, two central compiler problems. Combinatorial optimization has the potential to solve these problems optimally and to exploit processor-specific features readily. Our approach is the first to leverage this potential in practice: it captures the complete set of program transformations used in state-of-the-art compilers, scales to medium-sized functions of up to 1000 instructions, and generates executable code. This level of practicality is reached by using constraint programming, a particularly suitable combinatorial optimization technique. Unison, the implementation of our approach, is open source, used in industry, and integrated with the LLVM toolchain.

    An extensive evaluation of estimated speed, code size, and scalability confirms that Unison generates better code than LLVM while scaling to medium-sized functions. The evaluation uses systematically selected benchmarks from MediaBench and SPEC CPU2006 and different processor architectures (Hexagon, ARM, MIPS). Mean estimated speedup ranges from 1% to 9.3% and mean code size reduction ranges from 0.8% to 3.9% for the different architectures. Executing the generated code on Hexagon confirms that the estimated speedup indeed results in actual speedup. Given a fixed time limit, Unison solves optimally functions of up to 647 instructions, delivers improved solutions for functions of up to 874 instructions, and achieves more than 85% of the potential speed for 90% of the functions on Hexagon.

    The results in this paper show that our combinatorial approach can be used in practice to trade compilation time for code quality beyond the usual compiler optimization levels, fully exploit processor-specific features, and identify improvement opportunities in existing heuristic algorithms.

  • 23.
    Castañeda Lozano, Roberto
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS (Swedish Institute of Computer Science).
    Schulte, Christian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Survey on Combinatorial Register Allocation and Instruction Scheduling2018Inngår i: ACM Computing Surveys, ISSN 0360-0300, E-ISSN 1557-7341Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to increase instruction-level parallelism) are essential tasks for generating efficient assembly code in a compiler. In the last three decades, combinatorial optimization has emerged as an alternative to traditional, heuristic algorithms for these two tasks. Combinatorial optimization approaches can deliver optimal solutions according to a model, can precisely capture trade-offs between conflicting decisions, and are more flexible at the expense of increased compilation time.

    This paper provides an exhaustive literature review and a classification of combinatorial optimization approaches to register allocation and instruction scheduling, with a focus on the techniques that are most applied in this context: integer programming, constraint programming, partitioned Boolean quadratic programming, and enumeration. Researchers in compilers and combinatorial optimization can benefit from identifying developments, trends, and challenges in the area; compiler practitioners may discern opportunities and grasp the potential benefit of applying combinatorial optimization.

  • 24.
    Castañeda Lozano, Roberto
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS, Box 1263, S-16440 Kista, Sweden..
    Schulte, Christian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. RISE SICS, Box 1263, S-16440 Kista, Sweden..
    Survey on Combinatorial Register Allocation and Instruction Scheduling2019Inngår i: ACM Computing Surveys, ISSN 0360-0300, E-ISSN 1557-7341, Vol. 52, nr 3, artikkel-id 62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to increase instruction-level parallelism) are essential tasks for generating efficient assembly code in a compiler. In the past three decades, combinatorial optimization has emerged as an alternative to traditional, heuristic algorithms for these two tasks. Combinatorial optimization approaches can deliver optimal solutions according to a model, can precisely capture trade-offs between conflicting decisions, and are more flexible at the expense of increased compilation time. This article provides an exhaustive literature review and a classification of combinatorial optimization approaches to register allocation and instruction scheduling, with a focus on the techniques that are most applied in this context: integer programming, constraint programming, partitioned Boolean quadratic programming, and enumeration. Researchers in compilers and combinatorial optimization can benefit from identifying developments, trends, and challenges in the area; compiler practitioners may discern opportunities and grasp the potential benefit of applying combinatorial optimization.

  • 25.
    Castegren, Elias
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Clarke, D.
    Fernandez-Reyes, K.
    Wrigstad, T.
    Yang, A. M.
    Attached and detached closures in actors2018Inngår i: AGERE 2018 - Proceedings of the 8th ACM SIGPLAN International Workshop on Programming Based on Actors, Agents, and Decentralized Control, co-located with SPLASH 2018, Association for Computing Machinery (ACM), 2018, s. 54-61Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Expressive actor models combine aspects of functional programming into the pure actor model enriched with futures. Such functional features include first-class closures which can be passed between actors and chained on futures. Combined with mutable objects, this opens the door to race conditions. In some situations, closures may not be evaluated by the actor that created them yet may access fields or objects owned by that actor. In other situations, closures may be safely fired off to run as a separate task. This paper discusses the problem of who can safely evaluate a closure to avoid race conditions, and presents the current solution to the problem adopted by the Encore language. The solution integrates with Encore’s capability type system, which influences whether a closure is attached and must be evaluated by the creating actor, or whether it can be detached and evaluated independently of its creator. Encore’s current solution to this problem is not final or optimal. We conclude by discussing a number of open problems related to dealing with closures in the actor model.

  • 26.
    Castegren, Elias
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Wrigstad, Tobias
    Uppsala Univ, Uppsala, Sweden..
    OOlong: A Concurrent Object Calculus for Extensibility and Reuse2018Inngår i: ACM SIGAPP Applied Computing Review, ISSN 1559-6915, E-ISSN 1931-0161, Vol. 18, nr 4, s. 47-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present OOlong, an object calculus with interface inheritance, structured concurrency and locks. The goal of the calculus is extensibility and reuse. The semantics are therefore available in a version for LATEX typesetting (written in Ott), a mechanised version for doing rigorous proofs in Coq, and a prototype interpreter (written in OCaml) for typechecking an running OOlong programs.

  • 27. Cremona, F.
    et al.
    Lee, E. A.
    Lohstroh, M.
    Masin, M.
    Broman, David
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Tripakis, S.
    Hybrid Co-simulation: It's about time2018Inngår i: Proceedings - 21st ACM/IEEE International Conference on Model Driven Engineering Languages and Systems, MODELS 2018, Association for Computing Machinery, Inc , 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Model-based design methodologies are commonly used in industry for the development of cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting the weaknesses of a particular tool, an alternative is to embrace heterogeneity and develop tool integration platforms and protocols to leverage the strengths from other environments. A fairly recent attempt in this direction is an open interface standard called Functional Mock-up Interface (FMI), which is focused on the convenient exchange and co-simulation of simulation models (Functional Mock-up Units, FMUs), primarily between component suppliers and OEMs. As it stands, FMI has reached acceptance in industry, but its specification (version 2.0) provides only limited support for hybrid co-simulation-simulating systems that mix continuous and discrete behaviors, which are commonly used to model CPSs. This paper identifies FMI's time representation based on floating-point numbers as a key problem, because it does not support well the discrete events that typically occur at the cyber-physical boundary; it is only suitable for modeling continuous dynamics without discrete behaviors. While time is a central concept in reasoning about the physical world, it is largely abstracted away when reasoning about the cyber world. As a result, the engineering methods for CPSs have misaligned abstractions between the physics domain, the mathematical domain used to model physics, the computational domain used to implement these mathematical abstractions for simulation, and the computational domain used on the cyber side of CPSs. The most common resolution for this conundrum is to adopt the naive Newtonian ideal model of time, where time is a real number known everywhere and advancing uniformly. But ironically, Newtonian time proves not so practical for hybrid co-simulation. The obvious reason is that digital computers do not work with real numbers. Whereas real numbers have infinite precision, their floating-point representation does not. This discrepancy leads to unpredictable quantization errors that may accumulate. Although real numbers can be compared for equality (e.g., to define “simultaneity”), it rarely makes sense to do so for floating-point numbers. We show that the approach taken in FMI (and many other modeling frameworks) that embraces a naive Newtonian physical model of time, and a cyber-approximation of this model using floating-point numbers, is inadequate for CPSs; it leads to models with unnecessarily inexplicable, nondeterministic, and complex behaviors. Our analysis concludes that a model of time that solely uses integers solves many of these problems. Specifically, we propose to use a 64-bit unsigned integer representation with arbitrary resolution, given as a power of ten, allowing model parameters specified in decimal to be represented exactly (granted ample resolution). Integer arithmetic is computationally efficient, and, for well-chosen resolutions, this representation will tolerate very long simulations without overflow. It is also easily converted to and from floating-point representations, albeit not losslessly. Given the vast range of time scales used across different simulation models, we believe that choosing a fixed universal time resolution does not make sense. Instead, we describe an algorithm that picks an adequate time resolution for a particular model and we provide procedures for time quantization needed to reconcile discrepacies between internal time representations of co-simulated FMUs. We propose concrete extensions to the FMI standard for the support of hybrid co-simulation that enable the use of integer time, automatic choice of time resolution, and the use of absent signals. We explain in detail how these extensions can be implemented mod-ularly within the frameworks of existing simulation environments and with support for legacy FMUs and superdense time.

  • 28.
    Danglot, Benjamin
    et al.
    Inria Lille Nord Europe, Parc Sci Haute Borne 40,Ave Halley,Bat A,Pk Plaza, F-59650 Villeneuve Dascq, France..
    Vera-Perez, Oscar Luis
    Inria Rennes Bretagne Atlantique, Campus Beaulieu,263 Ave Gen Leclerc, F-35042 Rennes, France..
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Programvaruteknik och datorsystem, SCS.
    Monperrus, Martin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Teoretisk datalogi, TCS.
    Automatic test improvement with DSpot: a study with ten mature open-source projects2019Inngår i: Journal of Empirical Software Engineering, ISSN 1382-3256, E-ISSN 1573-7616, Vol. 24, nr 4, s. 2603-2635Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the literature, there is a rather clear segregation between manually written tests by developers and automatically generated ones. In this paper, we explore a third solution: to automatically improve existing test cases written by developers. We present the concept, design and implementation of a system called DSpot, that takes developer-written test cases as input (JUnit tests in Java) and synthesizes improved versions of them as output. Those test improvements are given back to developers as patches or pull requests, that can be directly integrated in the main branch of the test code base. We have evaluated DSpot in a deep, systematic manner over 40 real-world unit test classes from 10 notable and open-source software projects. We have amplified all test methods from those 40 unit test classes. In 26/40 cases, DSpot is able to automatically improve the test under study, by triggering new behaviors and adding new valuable assertions. Next, for ten projects under consideration, we have proposed a test improvement automatically synthesized by DSpot to the lead developers. In total, 13/19 proposed test improvements were accepted by the developers and merged into the main code base. This shows that DSpot is capable of automatically improving unit-tests in real-world, large scale Java software.

  • 29.
    Danglot, Benjamin
    et al.
    INRIA, Lille, France..
    Vera-Perez, Oscar
    INRIA, Rennes, France..
    Yu, Zhongxing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Teoretisk datalogi, TCS.
    Zaidman, Andy
    Delft Univ Technol, Delft, Netherlands..
    Monperrus, Martin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Teoretisk datalogi, TCS.
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Datavetenskap, Programvaruteknik och datorsystem, SCS.
    A snowballing literature study on test amplification2019Inngår i: Journal of Systems and Software, ISSN 0164-1212, E-ISSN 1873-1228, Vol. 157, artikkel-id UNSP 110398Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adoption of agile approaches has put an increased emphasis on testing, resulting in extensive test suites. These suites include a large number of tests, in which developers embed knowledge about meaningful input data and expected properties as oracles. This article surveys works that exploit this knowledge to enhance manually written tests with respect to an engineering goal (e.g., improve coverage or refine fault localization). While these works rely on various techniques and address various goals, we believe they form an emerging and coherent field of research, which we coin "test amplification". We devised a first set of papers from DBLP, searching for all papers containing "test" and "amplification" in their title. We reviewed the 70 papers in this set and selected the 4 papers that fit the definition of test amplification. We use them as the seeds for our snowballing study, and systematically followed the citation graph. This study is the first that draws a comprehensive picture of the different engineering goals proposed in the literature for test amplification. We believe that this survey will help researchers and practitioners entering this new field to understand more quickly and more deeply the intuitions, concepts and techniques used for test amplification.

  • 30.
    Durieux, Thomas
    et al.
    Univ Lille, Lille, France.;INRIA, Le Chesnay, France..
    Hamadi, Youssef
    Ecole Polytech, Palaiseau, France..
    Yu, Zhongxing
    Univ Lille, Lille, France.;INRIA, Le Chesnay, France..
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Monperrus, Martin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teoretisk datalogi, TCS.
    Exhaustive Exploration of the Failure-oblivious Computing Search Space2018Inngår i: 2018 IEEE 11TH INTERNATIONAL CONFERENCE ON SOFTWARE TESTING, VERIFICATION AND VALIDATION (ICST), IEEE Press, 2018, s. 139-149Konferansepaper (Fagfellevurdert)
    Abstract [en]

    High-availability of software systems requires automated handling of crashes in presence of errors. Failure-oblivious computing is one technique that aims to achieve high availability. We note that failure-obliviousness has not been studied in depth yet, and there is very few study that helps understand why failure-oblivious techniques work. In order to make failure-oblivious computing to have an impact in practice, we need to deeply understand failure-oblivious behaviors in software. In this paper, we study, design and perform an experiment that analyzes the size and the diversity of the failure-oblivious behaviors. Our experiment consists of exhaustively computing the search space of 16 field failures of large-scale open-source Java software. The outcome of this experiment is a much better understanding of what really happens when failure-oblivious computing is used, and this opens new promising research directions.

  • 31.
    Edman, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Sequential Pattern Mining on Electronic Medical Records for Finding Optimal Clinical Pathways2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Electronic Medical Records (EMRs) are digital versions of paper charts, used to record the treatment of different patients in hospitals. Clinical pathways are used as guidelines for how to treat different diseases, determined by observing outcomes from previous treatments. Sequential pattern mining is a version of data mining where the data mined is organized in sequences. It is a common research topic in data mining with many new variations on existing algorithms being introduced frequently. In a previous report, the sequential pattern mining algorithm PrefixSpan was used to mine patterns in EMRs to verify or suggest new clinical pathways. It was found to only be able to verify pathways partially. One of the reasons stated for this was that PrefixSpan was too inefficient to be able to mine at a low enough support to consider some items. In this report CSpan is used instead, since it is supposed to outperform PrefixSpan by up to two orders of magnitude, in order to improve runtime and thereby address the problems mentioned in the previous work. The results show that CSpan did indeed improve the runtime and the algorithm was able to mine at a lower minimum support. However, the output was only barely improved.

  • 32.
    Engelin, Martin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    CapsNet Comprehension of Objects in Different Rotational Views: A comparative study of capsule and convolutional networks2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Capsule network (CapsNet) is a new and promising approach to computer vision. In the small amount of research published so far, it has shown to be good at generalizing complex objects and perform well even when the images are skewed or the objects are seen from unfamiliar viewpoints. This thesis further tests this ability of CapsNetby comparing it to convolutional networks (ConvNets) on the task to understand images of clothing in different rotational views. Even though the ConvNets have a higher classification accuracy than CapsNets, the results indicate that CapsNets are better at understanding the clothes when viewed in different rotational views.

  • 33.
    Fernando, Tharidu
    et al.
    KTH.
    Gureev, Nikita
    KTH.
    Matskin, Mihhail
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Zwick, M.
    Natschlager, T.
    WorkflowDSL: Scalable Workflow Execution with Provenance for Data Analysis Applications2018Inngår i: Proceedings - International Computer Software and Applications Conference, IEEE Computer Society , 2018, s. 774-779Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Data analysis projects typically use different programming languages (from Python for prototyping to C++ for support of runtime constraints) at their different stages by different experts. This creates a need for a data processing framework that is re-usable across multiple programming languages and supports collaboration of experts. In this work, we discuss implementation of a framework which uses a Domain Specific Language (DSL), called WorkflowDSL, that enables domain experts to collaborate on fine-tuning workflows. The framework includes support for parallel execution without any specialized code. It also provides a provenance capturing framework that enables users to analyse past executions and retrieve complete lineage of any data item generated. Graph database is used for storing provenance data. Advantages of usage of a graph database compare to relational databases are demonstrated. Experiments which were performed using a real-world scientific workflow from the bioinformatics domain and industrial data analysis models show that users were able to execute workflows efficiently when using WorkflowDSL for workflow composition and Python for task implementations. Moreover, we show that capturing provenance data can be useful for analysing past workflow executions.

  • 34. Galindo, J. A.
    et al.
    Alférez, M.
    Acher, M.
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Benavides, D.
    MOTIV: Selección de pruebas para algoritmos de detección de movimiento en vídeos usando técnicas de líneas de productos software2018Inngår i: Actas de las 23rd Jornadas de Ingenieria del Software y Bases de Datos, JISBD 2018, Sistedes , 2018Konferansepaper (Fagfellevurdert)
  • 35.
    Gammerman, Alexander
    et al.
    Royal Holloway Univ London, Egham, Surrey, England..
    Vovk, Vladimir
    Royal Holloway Univ London, Egham, Surrey, England..
    Boström, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Carlsson, Lars
    Stena Line AB, Gothenburg, Sweden..
    Conformal and probabilistic prediction with applications: editorial2019Inngår i: Machine Learning, ISSN 0885-6125, E-ISSN 1573-0565, Vol. 108, nr 3, s. 379-380Artikkel i tidsskrift (Annet vitenskapelig)
  • 36.
    Ghoorchian, Kambiz
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Girdzijauskas, Sarunas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Spatio-Temporal Multiple Geo-Location Identification on Twitter2018Inngår i: Proceedings - 2018 IEEE International Conference on Big Data, Big Data 2018 / [ed] Abe, N Liu, H Pu, C Hu, X Ahmed, N Qiao, M Song, Y Kossmann, D Liu, B Lee, K Tang, J He, J Saltz, J, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 3412-3421Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Twitter Geo-tags that indicate the exact location of messages have many applications from localized opinion mining during elections to efficient traffic management in critical situations. However, less than 6% of Tweets are Geo-tagged, which limits the implementation of those applications. There are two groups of solutions: content and network-based. The first group uses location indicative factors like URLs and topics, extracted from the content of tweets, to infer Geo-location for non geoactive users, whereas the second group benefits from friendship ties in the underlying social network graph. Friendship ties are better predictors compared to content information because they are less noisy and often follow the natural human spatial movement patterns. However, their prediction's accuracy is still limited because they ignore the temporal aspects of human behavior and always assume a single location per user. This research aims to extend the current network-based approaches by taking users' temporal dimension into account. We assume multiple locations per user during different time-slots and hypothesize that location predictability varies depending on the time and the properties of the social membership group. Thus, we propose a hierarchical solution to apply temporal categorizations on top of social network partitioning for multiple location prediction for users in Online Social Networks (OSNs) like Twitter. Given a largescale Twitter dataset, we show that users' location predictability exhibits different behavior in different time-slots and different social groups. We find that there are specific conditions where users are more predictable in terms of Geo-location. Our solution outperforms the state-of-the-art by improving the prediction accuracy by 16:6% in terms of Median Error Distance (MED) over the same recall.

  • 37. Gomes, Claudio
    et al.
    Thule, Casper
    Broman, David
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Larsen, Peter Gorm
    Vangheluwe, Hans
    Co-Simulation: A Survey2018Inngår i: ACM Computing Surveys, ISSN 0360-0300, E-ISSN 1557-7341, Vol. 51, nr 3, artikkel-id 49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modeling and simulation techniques are today extensively used both in industry and science. Parts of larger systems are, however, typically modeled and simulated by different techniques, tools, and algorithms. In addition, experts from different disciplines use various modeling and simulation techniques. Both these facts make it difficult to study coupled heterogeneous systems. Co-simulation is an emerging enabling technique, where global simulation of a coupled system can be achieved by composing the simulations of its parts. Due to its potential and interdisciplinary nature, cosimulation is being studied in different disciplines but with limited sharing of findings. In this survey, we study and survey the state-of-the-art techniques for co-simulation, with the goal of enhancing future research and highlighting the main challenges. To study this broad topic, we start by focusing on discrete-event-based co-simulation, followed by continuous-time-based co-simulation. Finally, we explore the interactions between these two paradigms, in hybrid co-simulation. To survey the current techniques, tools, and research challenges, we systematically classify recently published research literature on co-simulation, and summarize it into a taxonomy. As a result, we identify the need for finding generic approaches for modular, stable, and accurate coupling of simulation units, as well as expressing the adaptations required to ensure that the coupling is correct.

  • 38.
    Gomez-Boix, Alejandro
    et al.
    Univ Rennes, INRIA, CNRS, IRISA, Rennes, France. audry, Benoit.
    perdrix, Pierre
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Hiding in the Crowd: an Analysis of the Effectiveness of Browser ngerprinting at Large Scale2018Inngår i: WEB CONFERENCE 2018: PROCEEDINGS OF THE WORLD WIDE WEB CONFERENCE (WW2018), Association for Computing Machinery (ACM), 2018, s. 309-318Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Browser fingerprinting is a stateless technique, which consists in collecting a wide range of data about a device through browser APIs. Past studies have demonstrated that modern devices present so much diversity that fingerprints can be exploited to identify and track users online. With this work, we want to evaluate if browser fingerprinting is still effective at uniquely identifying a large group of users when analyzing millions of fingerprints over a few months. We collected 2,067,942 browser fingerprints from one of the top 15 French websites. The analysis of this novel dataset sheds a new light on the ever-growing browser fingerprinting domain. The key insight is that the percentage of unique fingerprints in our dataset is much lower than what was reported in the past: only 33.6% of fingerprints are unique by opposition to over 80% in previous studies. We show that non-unique fingerprints tend to be fragile. If some features of the fingerprint change, it is very probable that the fingerprint will become unique. We also confirm that the current evolution of web technologies is benefiting users' privacy significantly as the removal of plugins brings down substantively the rate of unique desktop machines.

  • 39.
    Hakimzadeh, Kamal
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Dowling, Jim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. Logical Clocks AB, Stockholm, Sweden.
    Karamel: A System for Timely Provisioning Large-Scale Software Across IaaS Clouds2019Inngår i: 2019 IEEE 12th International Conference on Cloud Computing (CLOUD), IEEE Computer Society, 2019, s. 391-395, artikkel-id 8814511Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cloud-native systems and application software platforms are becoming increasingly complex, and, ideally, they are expected to be quick to launch, elastic, portable across different cloud environments and easily managed. However, as cloud applications increase in complexity, so do the resultant challenges in configuring such applications, and orchestrating the deployment of their constituent services on potentially different cloud operating systems and environments.

    This paper presents a new orchestration system called Karamel that addresses these challenges by providing a cloud-independent orchestration service for deploying and configuring cloud applications and platforms across different environments. In Karamel, we model configuration routines with their dependencies in composable modules, and we achieve a high level of configuration/deployment parallelism by using techniques such as DAG traversal control logic, dataflow variable binding, and parallel actuation. In Karamel, complex distributed deployments are specified declaratively in a compact YAML syntax, and cluster definitions can be validated using an external artifact repository (GitHub).

  • 40.
    Hakimzadeh, Kamal
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Dowling, Jim
    Logical Clocks AB, Stockholm, Sweden.
    Ops-Scale: Scalable and Elastic Cloud Operations by a Functional Abstraction and Feedback Loops2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recent research has proposed new techniques to streamline the autoscaling of cloud applications, but little effort has been made to advance configuration management (CM) systems for such elastic operations. Existing practices use CM systems, from the DevOps paradigm, to automate operations. However, these practices still require human intervention to program ad hoc procedures to fully automate reconfiguration. Moreover, even after careful programming of cloud operations, the backing models are insufficient for re-running such programs unchanged in other platforms---which implies an overhead in rewriting the programs.

    We argue that CM programs can be designed to be deployment-agnostic and highly elastic with well-defined abstractions. In this paper, we introduce our abstraction based on declarative functional programming, and we demonstrate it using a feedback loop control mechanism. Our proposal, called Ops-Scale, is a family of cloud operations that are derived by making a functional abstraction over existing configuration programs. The hypothesis in this paper is twofold: 1) it should be possible to make a highly declarative CM system rich enough to capture fine-grained reconfigurations of autoscaling automatically, and; 2) that a program written for a specific deployment can be re-used in other deployments. To test this hypothesis, we have implemented an open source configuration engine called Karamel that is already used in industry for large-scale cluster deployments. Results show that at scale Ops-Scale can capture a polynomial order of reconfiguration growth in a fully automated manner. In practice, recent deployments have demonstrated that Karamel can provision clusters of 100 virtual machines consisting of many-layers distributed services on Google's IaaS Cloud in 'less than 10 minutes'.

  • 41.
    Hakimzadeh, Kamal
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Nicholson, P. K.
    Lugones, D.
    Auto-scaling with apprenticeship learning2018Inngår i: SoCC 2018 - Proceedings of the 2018 ACM Symposium on Cloud Computing, Association for Computing Machinery (ACM), 2018, s. 512-512Konferansepaper (Fagfellevurdert)
  • 42.
    Halin, Axel
    et al.
    Univ Namur, Fac Comp Sci, NaDI, PReCISE, Namur, Belgium..
    Nuttinck, Alexandre
    CETIC, Charleroi, Belgium..
    Acher, Mathieu
    Univ Rennes, IRISA, CNRS, INRIA, Rennes, France..
    Devroey, Xavier
    Delft Univ Technol, SERG, Delft, Netherlands..
    Perrouin, Gilles
    Univ Namur, Fac Comp Sci, NaDI, PReCISE, Namur, Belgium..
    Baudry, Benoit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Test them all, is it worth it?: Assessing configuration sampling on the JHipster Web development stack2019Inngår i: Journal of Empirical Software Engineering, ISSN 1382-3256, E-ISSN 1573-7616, Vol. 24, nr 2, s. 674-717Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many approaches for testing configurable software systems start from the same assumption: it is impossible to test all configurations. This motivated the definition of variability-aware abstractions and sampling techniques to cope with large configuration spaces. Yet, there is no theoretical barrier that prevents the exhaustive testing of all configurations by simply enumerating them if the effort required to do so remains acceptable. Not only this: we believe there is a lot to be learned by systematically and exhaustively testing a configurable system. In this case study, we report on the first ever endeavour to test all possible configurations of the industry-strength, open source configurable software system JHipster, a popular code generator for web applications. We built a testing scaffold for the 26,000+ configurations of JHipster using a cluster of 80 machines during 4 nights for a total of 4,376 hours (182 days) CPU time. We find that 35.70% configurations fail and we identify the feature interactions that cause the errors. We show that sampling strategies (like dissimilarity and 2-wise): (1) are more effective to find faults than the 12 default configurations used in the JHipster continuous integration; (2) can be too costly and exceed the available testing budget. We cross this quantitative analysis with the qualitative assessment of JHipster's lead developers.

  • 43.
    Hammar, Kim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Deep Text Mining of Instagram Data Without Strong Supervision2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    With the advent of social media, our online feeds increasingly consist of short, informal, and unstructured text. This data can be analyzed for the purpose of improving user recommendations and detecting trends. The grand volume of unstructured text that is available makes the intersection of text processing and machine learning a promising avenue of research. Current methods that use machine learning for text processing are in many cases dependent on annotated training data. However, considering the heterogeneity and variability of social media, obtaining strong supervision for social media data is in practice both difficult and expensive. In light of this limitation, a belief that has put its marks on this thesis is that the study of text mining methods that can be applied without strong supervision is of a higher practical interest.

    This thesis investigates unsupervised methods for scalable processing of text from social media. Particularly, the thesis targets a classification and extraction task in the fashion domain on the image-sharing platform Instagram. Instagram is one of the largest social media platforms, containing both text and images. Still, research on text processing in social media is to a large extent limited to Twitter data, and little attention has been paid to text mining of Instagram data. The aim of this thesis is to broaden the scope of state-of-the-art methods for information extraction and text classification to the unsupervised setting, working with informal text on Instagram. Its main contributions are (1) an empirical study of text from Instagram; (2) an evaluation of word embeddings for Instagram text; (3) a distributed implementation of the FastText algorithm; (4) a system for fashion attribute extraction in Instagram using word embeddings; and (5) a multi-label clothing classifier for Instagram text, built with deep learning techniques and minimal supervision.

    The empirical study demonstrates that the text distribution on Instagram exhibits the long-tail phenomenon, that the text is just as noisy as have been reported in studies on Twitter text, and that comment sections are multi-lingual. In experiments with word embeddings for Instagram, the importance of hyperparameter tuning is manifested and a mismatch between pre-trained embeddings and social media is observed. Furthermore, that word embeddings are a useful asset for information extraction is confirmed. Experimental results show that word embeddings beats a baseline that uses Levenshtein distance on the task of extracting fashion attributes from Instagram. The results also show that the distributed implementation of FastText reduces the time it takes to train word embeddings with a factor that scales with the number of machines used for training. Finally, our research demonstrates that weak supervision can be used to train a deep classifier, achieving an F1 score of 0.61 on the task of classifying clothes in Instagram posts based only on the associated text, which is on par with human performance.

  • 44.
    Hammar, Kim
    et al.
    KTH.
    Jaradat, Shatha
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Dokoohaki, Nima
    KTH.
    Matskin, Mihhail
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Deep Text Mining of Instagram Data Without Strong Supervision2018Inngår i: Proceedings - 2018 IEEE/WIC/ACM International Conference on Web Intelligence, WI 2018, IEEE, 2018, s. 158-165Konferansepaper (Fagfellevurdert)
    Abstract [en]

    With the advent of social media, our online feeds increasingly consist of short, informal, and unstructured text. This textual data can be analyzed for the purpose of improving user recommendations and detecting trends. Instagram is one of the largest social media platforms, containing both text and images. However, most of the prior research on text processing in social media is focused on analyzing Twitter data, and little attention has been paid to text mining of Instagram data. Moreover, many text mining methods rely on annotated training data, which in practice is both difficult and expensive to obtain. In this paper, we present methods for unsupervised mining of fashion attributes from Instagram text, which can enable a new kind of user recommendation in the fashion domain. In this context, we analyze a corpora of Instagram posts from the fashion domain, introduce a system for extracting fashion attributes from Instagram, and train a deep clothing classifier with weak supervision to classify Instagram posts based on the associated text. With our experiments, we confirm that word embeddings are a useful asset for information extraction. Experimental results show that information extraction using word embeddings outperforms a baseline that uses Levenshtein distance. The results also show the benefit of combining weak supervision signals using generative models instead of majority voting. Using weak supervision and generative modeling, an F1 score of 0.61 is achieved on the task of classifying the image contents of Instagram posts based solely on the associated text, which is on level with human performance. Finally, our empirical study provides one of the few available studies on Instagram text and shows that the text is noisy, that the text distribution exhibits the long-tail phenomenon, and that comment sections on Instagram are multi-lingual.

  • 45.
    Hollmen, Jaakko
    et al.
    Aalto Univ, Dept Comp Sci, Espoo, Finland..
    Asker, Lars
    Stockholm Univ, Dept Comp & Syst Sci, Stockholm, Sweden..
    Karlsson, Isak
    Stockholm Univ, Dept Comp & Syst Sci, Stockholm, Sweden..
    Papapetrou, Panagiotis
    Stockholm Univ, Dept Comp & Syst Sci, Stockholm, Sweden..
    Boström, Henrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Wikner, Birgitta Norstedt
    Karolinska Inst, Dept Med, Ctr Pharmacoepidemiol CPE, Stockholm, Sweden..
    Ohman, Inger
    Karolinska Inst, Dept Med, Ctr Pharmacoepidemiol CPE, Stockholm, Sweden..
    Exploring epistaxis as an adverse effect of anti-thrombotic drugs and outdoor temperature2018Inngår i: 11TH ACM INTERNATIONAL CONFERENCE ON PERVASIVE TECHNOLOGIES RELATED TO ASSISTIVE ENVIRONMENTS (PETRA 2018), ASSOC COMPUTING MACHINERY , 2018, s. 1-4Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Electronic health records contain a wealth of epidemiological information about diseases at the population level. Using a database of medical diagnoses and drug prescriptions in electronic health records, we investigate the correlation between outdoor temperature and the incidence of epistaxis over time for two groups of patients. One group consists of patients that had been diagnosed with epistaxis and also been prescribed at least one of the three anti-thrombotic agents: Warfarin, Apixaban, or Rivaroxaban. The other group consists of patients that had been diagnosed with epistaxis and not been prescribed any of the three anti-thrombotic drugs. We find a strong negative correlation between the incidence of epistaxis and outdoor temperature for the group that had not been prescribed any of the three anti-thrombotic drugs, while there is a weaker correlation between incidence of epistaxis and outdoor temperature for the other group. It is, however, clear that both groups are affected in a similar way, such that the incidence of epistaxis increases with colder temperatures.

  • 46.
    Håkansson, Anne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Ipsum - An Approach to Smart Volatile ICT-Infrastructures for Smart Cities and Communities2018Inngår i: Procedia Computer Science, Elsevier B.V. , 2018, s. 2107-2116Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Information and Communication Technology (ICT)-infrastructures are increasingly important for enabling technology within Smart society with Smart cities and communitieS. An ICT-infrastructure handles data and information and encompasses devices and networks, protocols and procedures including Internet, Internet of Things and Cyber-Physical Systems. The current challenges of ICT-infrastructures are delivering Services and applications that are requested by users, such as residents, public organisations and institutionS. These Services and applications must be combined to enhance and enrich the environment and provide personalised ServiceS. This requires radical changes in technology, such as dynamic ICT-infrastructures, which should dynamically provide requested Services to be able to build Smart societieS. This paper is about pursuing Smart and connected cities and communities by creating Smart volatile ICT-infrastructures for Smart cities and communities, called Ipsum. The infrastructure is of multidisciplinary art and includes different kinds of hardware, software, artificial intelligence techniques depending on the available parts and the Services to be delivered. The goal is to provide a powerful and smart, and cost-saving volatile ICT-infrastructure with person-centred, ubiquitous and malleable parts, i.e., devices, sensors and ServiceS. Volatile means in real-time constitute a volatile network of devices and deploying it into cities and communitieS. Ipsum will be Smart everywhere by collaborating with several different hardware and software Systems and cooperating to perform complex taskS. By including ubiquitous and malleable parts in the infrastructure, Ipsum can facilitate an informed and engaged populace.

  • 47. Ingmar, Linnea
    et al.
    Schulte, Christian
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Making Compact-Table Compact2018Inngår i: 24th International Conference on the Principles and Practice of Constraint Programming, CP 2018, Springer, 2018, Vol. 11008, s. 210-218Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The compact-table propagator for table constraints appears to be a strong candidate for inclusion into any constraint solver due to its efficiency and simplicity. However, successful integration into a constraint solver based on copying rather than trailing is not obvious: while the underlying bit-set data structure is sparse for efficiency it is not compact for memory, which is essential for a copying solver. The paper introduces techniques to make compact-table an excellent fit for a copying solver. The key is to make sparse bit-sets dynamically compact (only their essential parts occupy memory and their implementation is dynamically adapted during search) and tables shared (their read-only parts are shared among copies). Dynamically compact bit-sets reduce peak memory by 7.2% and runtime by 13.6% on average and by up to 66.3% and 33.2%. Shared tables even further reduce runtime and memory usage. The reduction in runtime exceeds the reduction in memory and a cache analysis indicates that our techniques might also be beneficial for trailing solvers. The proposed implementation has replaced Gecode’s original implementations as it runs on average almost an order of magnitude faster while using half the memory.

  • 48.
    Ismail, Mahmoud
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Bonds, August
    KTH.
    Niazi, Salman
    Logical Clocks AB.
    Haridi, Seif
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Dowling, Jim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Scalable Block Reporting for HopsFS2019Inngår i: 2019 IEEE International Congress on Big Data (BigData Congress), 2019, s. 157-164Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Distributed hierarchical file systems typically de- couple the storage of the file system’s metadata from the data (file system blocks) to enable the scalability of the file system. This decoupling, however, requires the introduction of a periodic synchronization protocol to ensure the consistency of the file system’s metadata and its blocks. Apache HDFS and HopsFS implement a protocol, called block reporting, where each data server periodically sends ground truth information about all its file system blocks to the metadata servers, allowing the metadata to be synchronized with the actual state of the data blocks in the file system. The network and processing overhead of the existing block reporting protocol, however, increases with cluster size, ultimately limiting cluster scalability. In this paper, we introduce a new block reporting protocol for HopsFS that reduces the protocol bandwidth and processing overhead by up to three orders of magnitude, compared to HDFS/HopsFS’ existing protocol. Our new protocol removes a major bottleneck that prevented HopsFS clusters scaling to tens of thousands of servers.

  • 49.
    Ismail, Mahmoud
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Ronström, Mikael
    Haridi, Seif
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    Dowling, Jim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS.
    ePipe: Near Real-Time Polyglot Persistence of HopsFS Metadata2019Inngår i: 2019 19th IEEE/ACM International Symposium on Cluster, Cloud and Grid Computing (CCGRID), 2019, s. 92-101Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Distributed OLTP databases are now used to manage metadata for distributed file systems, but they cannot also efficiently support complex queries or aggregations. To solve this problem, we introduce ePipe, a databus that both creates a consistent change stream for a distributed, hierarchical file system (HopsFS) and eventually delivers the correctly ordered stream with low latency to downstream clients. ePipe can be used to provide polyglot storage for file system metadata, allowing metadata queries to be handled by the most efficient engine for that query. For file system notifications, we show that ePipe achieves up to 56X throughput improvement over HDFS INotify and Trumpet with up to 3 orders of magnitude lower latency. For Spotify’s Hadoop workload, we show that ePipe can replicate all file system changes from HopsFS to Elasticsearch with an average replication lag of only 330 ms.

  • 50.
    Issa, Shady
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Programvaruteknik och datorsystem, SCS. INESC-ID, Instituto Superior Tecnico, Universidade de Lisboa.
    Techniques for Enhancing the Efficiency of Transactional Memory Systems2018Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    Transactional Memory (TM) is an emerging programming paradigm that drastically simplifies the development of concurrent applications by relieving programmers from a major source of complexity: how to ensure correct, yet efficient, synchronization of concurrent accesses to shared memory. Despite the large body of research devoted to this area, existing TM systems still suffer from severe limitations that hamper both their performance and energy efficiency.

    This dissertation tackles the problem of how to build efficient implementations of the TM abstraction by introducing innovative techniques that address three crucial limitations of existing TM systems by: (i) extending the effective capacity of Hardware TM (HTM) implementations; (ii) reducing the synchronization overheads in Hybrid TM (HyTM) systems; (iii) enhancing the efficiency of TM applications via energy-aware contention management schemes.

    The first contribution of this dissertation, named POWER8-TM (P8TM), addresses what is arguably one of the most compelling limitations of existing HTM implementations: the inability to process transactions whose footprint exceeds the capacity of the processor's cache. By leveraging, in an innovative way, two hardware features provided by IBM POWER8 processors, namely Rollback-only Transactions and Suspend/Resume, P8TM can achieve up to 7x performance gains in workloads that stress the capacity limitations of HTM.

    The second contribution is Dynamic Memory Partitioning-TM (DMP-TM), a novel Hybrid TM (HyTM) that offloads the cost of detecting conflicts between HTM and Software TM (STM) to off-the-shelf operating system memory protection mechanisms. DMP-TM's design is agnostic to the STM algorithm and has the key advantage of allowing for integrating, in an efficient way, highly scalable STM implementations that would, otherwise, demand expensive instrumentation of the HTM path. This allows DMP-TM to achieve up to 20x speedups compared to state of the art HyTM solutions in uncontended workloads.

    The third contribution, Green-CM, is an energy-aware Contention Manager (CM) that has two main innovative aspects: (i) a novel asymmetric design, which combines different back-off policies in order to take advantage of Dynamic Frequency and Voltage Scaling (DVFS) hardware capabilities, available in most modern processors; (ii) an energy efficient implementation of a fundamental building block for many CM implementations, namely, the mechanism used to back-off threads for a predefined amount of time. Thanks to its innovative design, Green-CM can reduce the Energy Delay Product by up to 2.35x with respect to state of the art CMs.

    All the techniques proposed in this dissertation share an important common feature that is essential to preserve the ease of use of the TM abstraction: the reliance on on-line self-tuning mechanisms that ensure robust performance even in presence of heterogeneous workloads, without requiring prior knowledge of the target workloads or architecture.

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