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Analysis of enterprise IT service availability: Enterprise architecture modeling for assessment, prediction, and decision-making
KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.ORCID iD: 0000-0003-2017-7914
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Information technology has become increasingly important to individuals and organizations alike. Not only does IT allow us to do what we always did faster and more effectively, but it also allows us to do new things, organize ourselves differently, and work in ways previously unimaginable. However, these advantages come at a cost: as we become increasingly dependent upon IT services, we also demand that they are continuously and uninterruptedly available for use. Despite advances in reliability engineering, the complexity of today's increasingly integrated systems offers a non-trivial challenge in this respect. How can high availability of enterprise IT services be maintained in the face of constant additions and upgrades, decade-long life-cycles, dependencies upon third-parties and the ever-present business-imposed requirement of flexible and agile IT services?

The contribution of this thesis includes (i) an enterprise architecture framework that offers a unique and action-guiding way to analyze service availability, (ii) identification of causal factors that affect the availability of enterprise IT services, (iii) a study of the use of fault trees for enterprise architecture availability analysis, and (iv) principles for how to think about availability management.

This thesis is a composite thesis of five papers. Paper 1 offers a framework for thinking about enterprise IT service availability management, highlighting the importance of variance of outage costs. Paper 2 shows how enterprise architecture (EA) frameworks for dependency analysis can be extended with Fault Tree Analysis (FTA) and Bayesian networks (BN) techniques. FTA and BN are proven formal methods for reliability and availability modeling. Paper 3 describes a Bayesian prediction model for systems availability, based on expert elicitation from 50 experts. Paper 4 combines FTA and constructs from the ArchiMate EA language into a method for availability analysis on the enterprise level. The method is validated by five case studies, where annual downtime estimates were always within eight hours from the actual values. Paper 5 extends the Bayesian prediction model from paper 3 and the modeling method from paper 4 into a full-blown enterprise architecture framework, expressed in a probabilistic version of the Object Constraint Language. The resulting modeling framework is tested in nine case studies of enterprise information systems.

Abstract [sv]

Informationsteknik blir allt viktigare för både enskilda individer och för organisationer. IT låter oss inte bara arbeta snabbare och effektivare med det vi redan gör, utan låter oss också göra helt nya saker, organisera oss annorlunda och arbeta på nya sätt. Tyvärr har dessa fördelar ett pris: i takt med att vi blir alltmer beroende av IT-tjänster ökar också våra krav på att de är ständigt tillgängliga för oss, utan avbrott. Trots att tillförlitlighetstekniken går framåt utgör dagens alltmer sammankopplade system en svår utmaning i detta avseende. Hur kan man säkerställa hög tillgänglighet hos IT-tjänster som ständigt byggs ut och uppgraderas, som har livscykler på tiotals år, som är beroende av tredjepartsleverantörer och som dessutom måste leva upp till verksamhetskrav på att vara flexibla och agila?

Den här avhandlingen innehåller (i) ett arkitekturramverk som på ett unikt sätt kan analysera IT-tjänsters tillgänglighet och ta fram rekommenderade åtgärder, (ii) ett antal identifierade kausalfaktorer som påverkar IT-tjänsters tillgänglighet, (iii) en studie av hur felträd kan användas för arkitekturanalys av tillgänglighet samt (iv) en uppsättning principer för beslutsfattande kring tillgänglighet.

Avhandlingen är en sammanläggningsavhandling med fem artiklar. Artikel 1 innehåller ett konceptuellt ramverk för beslutsfattande kring IT-tjänsters tillgänglighet som understryker vikten av variansen hos nertidskostnaderna. Artikel 2 visar hur ramverk för organisationsövergripande arkitektur (s.k. enterprise architecture -- EA) kan utvidgas med felträdsanalys (FTA) och bayesianska nätverk (BN) för analys av beroenden mellan komponenter. FTA och BN är bägge etablerade metoder för tillförlitlighets- och tillgänglighetsmodellering. Artikel 3 beskriver en bayesiansk prediktionsmodell för systemtillgänglighet, baserad på utlåtanden från 50 experter. Artikel 4 kombinerar FTA med modelleringselement från EA-ramverket ArchiMate till en metod för tillgänglighetsanalys på verksamhetsnivå. Metoden har validerats i fem fallstudier, där de estimerade årliga nertiderna alltid låg inom åtta timmar från de faktiska värdena. Artikel 5 utvidgar den bayesianska prediktionsmodellen från artikel 3 och modelleringsmetoden från artikel 4 till ett fullständigt EA-ramverk som uttrycks i en probabilistisk version av Object Constraint Language (OCL). Det resulterande modelleringsramverket har testats i nio fallstudier på verksamhetsstödjande IT-system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xiii, 39 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:032
Keyword [en]
Service Level Agreement, outage costs, Enterprise Architecture, enterprise IT service availability, decision-making, metamodeling, Enterprise Architecture analysis, Bayesian networks, fault trees, Predictive Probabilistic Architecture Modeling Framework
Keyword [sv]
Service Level Agreement, nertidskostnader, Enterprise Architecture, tillgänglighet hos IT-tjänster, beslutsfattande, metamodellering, arkitekturanalys, bayesianska nätverk, felträd, Predictive Probabilistic Architecture Modeling Framework
National Category
Information Systems
Identifiers
URN: urn:nbn:se:kth:diva-101946ISBN: 978-91-7501-443-2 (print)OAI: oai:DiVA.org:kth-101946DiVA: diva2:550059
Public defence
2012-10-31, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20120912

Available from: 2012-09-12 Created: 2012-09-06 Last updated: 2013-01-28Bibliographically approved
List of papers
1. Optimal IT service availability: Shorter outages, or fewer?
Open this publication in new window or tab >>Optimal IT service availability: Shorter outages, or fewer?
2012 (English)In: IEEE Transactions on Network and Service Management, ISSN 1932-4537, E-ISSN 1932-4537, Vol. 9, no 1, 22-33 p.Article in journal (Refereed) Published
Abstract [en]

High enterprise IT service availability is a key success factor throughout many industries. While understanding of the economic importance of availability management is becoming more widespread, the implications for management of Service Level Agreements (SLAs) and thinking about availability risk management are just beginning to unfold. This paper offers a framework within which to think about availability management, highlighting the importance of variance of outage costs. The importance of variance is demonstrated using simulations on existing data sets of revenue data. An important implication is that when outage costs are proportional to outage duration, more but shorter outages should be preferred to fewer but longer, in order to minimize variance. Furthermore, two archetypal cases where the cost of an outage depends non-linearly on its duration are considered. An optimal outage length is derived, and some guidance is also given for its application when the variance of hourly downtime costs is considered. The paper is concluded with a discussion about the feasibility of the method, its practitioner relevance and its implications for SLA management.

Keyword
availability, fault management, optimization techniques, policy-based management, Service level agreements, SLA management, Costs, Optimization, Risk management, Information technology
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-99539 (URN)10.1109/TNSM.2011.110811.110122 (DOI)2-s2.0-84858290402 (Scopus ID)
Note
QC 20120731Available from: 2012-07-31 Created: 2012-07-31 Last updated: 2017-12-07Bibliographically approved
2. Enterprise Architecture Dependency Analysis using Fault Trees and Bayesian Networks
Open this publication in new window or tab >>Enterprise Architecture Dependency Analysis using Fault Trees and Bayesian Networks
2009 (English)In: Proc. 42nd Annual Simulation Symposium, 2009, 209-216 p.Conference paper, Published paper (Refereed)
Abstract [en]

Analysis of dependencies between technical systems and business processes is an important part of the discipline of Enterprise Architecture (EA). However, EA models typically provide only visual and qualitative decision support. This paper shows how EA frameworks for dependency analysis can be extended into the realm of quantitative methods by use of the Fault Tree Analysis (FTA) and Bayesian networks (BN) techniques. Using DoDAF ? the Department of Defense Architecture Framework ? as an example, we provide a method for how these EA models can be adapted for use of FTA and BN. Furthermore, we use this method to perform dependency analysis and scenario evaluation on a sample DoDAF model.

Keyword
Enterprise Architecture, DoDAF, Fault Tree Analysis, Bayesian networks, dependency analysis
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-80663 (URN)2-s2.0-77953509232 (Scopus ID)
Conference
IR-EE-ICS_2009:004
Note
QC 20120215Available from: 2012-02-10 Created: 2012-02-10 Last updated: 2012-09-12Bibliographically approved
3. Availability of enterprise IT systems: an expert-based Bayesian framework
Open this publication in new window or tab >>Availability of enterprise IT systems: an expert-based Bayesian framework
2012 (English)In: Software quality journal, ISSN 0963-9314, E-ISSN 1573-1367, Vol. 20, no 2, 369-394 p.Article in journal (Refereed) Published
Abstract [en]

Ensuring the availability of enterprise IT systems is a challenging task. The factors that can bring systems down are numerous, and their impact on various system architectures is difficult to predict. At the same time, maintaining high availability is crucial in many applications, ranging from control systems in the electric power grid, over electronic trading systems on the stock market to specialized command and control systems for military and civilian purposes. This paper describes a Bayesian decision support model, designed to help enterprise IT systems decision makers evaluate the consequences of their decisions by analyzing various scenarios. The model is based on expert elicitation from 50 experts on IT systems availability, obtained through an electronic survey. The Bayesian model uses a leaky Noisy-OR method to weigh together the expert opinions on 16 factors affecting systems availability. Using this model, the effect of changes to a system can be estimated beforehand, providing decision support for improvement of enterprise IT systems availability. The Bayesian model thus obtained is then integrated within a standard, reliability block diagram-style, mathematical model for assessing availability on the architecture level. In this model, the IT systems play the role of building blocks. The overall assessment framework thus addresses measures to ensure high availability both on the level of individual systems and on the level of the entire enterprise architecture. Examples are presented to illustrate how the framework can be used by practitioners aiming to ensure high availability.

Keyword
Systems availability, High availability, Downtime, Bayesian networks, Noisy-OR, Expert elicitation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-80629 (URN)10.1007/s11219-011-9141-z (DOI)000303507800006 ()2-s2.0-84860493993 (Scopus ID)
Note
QC 20120531Available from: 2012-02-10 Created: 2012-02-10 Last updated: 2017-12-07Bibliographically approved
4. Enterprise Architecture Availability Analysis Using Fault Trees and Stakeholder Interviews
Open this publication in new window or tab >>Enterprise Architecture Availability Analysis Using Fault Trees and Stakeholder Interviews
Show others...
2014 (English)In: Enterprise Information Systems, ISSN 1751-7575, E-ISSN 1751-7583, Vol. 8, no 1, 1-25 p.Article in journal (Refereed) Published
Abstract [en]

The availability of enterprise information systems is a key concern for many organisations. This article describes a method for availability analysis based on Fault Tree Analysis and constructs from the ArchiMate enterprise architecture (EA) language. To test the quality of the method, several case-studies within the banking and electrical utility industries were performed. Input data were collected through stakeholder interviews. The results from the case studies were compared with availability of log data to determine the accuracy of the method's predictions. In the five cases where accurate log data were available, the yearly downtime estimates were within eight hours from the actual downtimes. The cost of performing the analysis was low; no case study required more than 20 man-hours of work, making the method ideal for practitioners with an interest in obtaining rapid availability estimates of their enterprise information systems.

Keyword
availability, enterprise architecture, probabilistic relational models, architecture analysis, fault tree analysis, stakeholder elicitation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-79641 (URN)10.1080/17517575.2011.647092 (DOI)000328473200001 ()2-s2.0-84890611982 (Scopus ID)
Note

QC 20140122

Available from: 2012-02-09 Created: 2012-02-09 Last updated: 2017-12-07Bibliographically approved
5. An architecture framework for enterprise IT service availability analysis
Open this publication in new window or tab >>An architecture framework for enterprise IT service availability analysis
2014 (English)In: Software and Systems Modeling, ISSN 1619-1366, E-ISSN 1619-1374, Vol. 13, no 4, 1417-1445 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an integrated enterprise architecture framework for qualitative and quantitative modeling and assessment of enterprise IT service availability. While most previous work has either focused on formal availability methods such as fault trees or qualitative methods such as maturity models, this framework offers a combination. First, a modeling and assessment framework is described. In addition to metamodel classes, relationships and attributes suitable for availability modeling, the framework also features a formal computational model written in a probabilistic version of the object constraint language. The model is based on 14 systemic factors impacting service availability and also accounts for the structural features of the service architecture. Second, the framework is empirically tested in nine enterprise information system case studies. Based on an initial availability baseline and the annual evolution of the 14 factors of the model, annual availability predictions are made and compared with the actual outcomes as reported in SLA reports and system logs. The practical usefulness of the method is discussed based on the outcomes of a workshop conducted with the participating enterprises, and some directions for future research are offered.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2014
Keyword
Systems availability, Service availability, Downtime, Noisy-OR, System quality analysis, Enterprise Architecture, ArchiMate, Metamodel, OCL
National Category
Information Systems
Identifiers
urn:nbn:se:kth:diva-101941 (URN)10.1007/s10270-012-0307-3 (DOI)000342493300011 ()2-s2.0-84911004529 (Scopus ID)
Note

QC 20141027. Updated from e-pub ahead of print to published.

Available from: 2013-02-04 Created: 2012-09-06 Last updated: 2017-12-07Bibliographically approved

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