Mälardalen University (MdH)

1. Computation, Composability and Quality AttributesIvica Crnkovic Mälardalen University, SwedenDepartment of Computer Science and Engineeringwww.idt.mdh.se/~icc, ivica.crnkovic@mdh.se

2. Mälardalen University (MdH) Mälardalen University, Vasteras (Västerås) Prof. in Software Engineering http://www.idt.mdh.se/~icc ivica.crnkovic@mdh.se • School of • Innovation, Design and Engineering • Software Engineering Division

3. Outline • Parti I • Properties (Quality attributes) • Part II • Composability vs. predictability of Quality Attributes • Classification of Quality attributes

4. Computation vs Composition • Computation • Abstraction + Automation (J.Wing) • What are the challenges; • Are there some things that are not computable (yet are part of software)

5. Part IFunctional andextra-functional properties

6. Properties • Attribute/property • “a construct whereby objects and individuals can be distinguished” • “a quality or trait belonging to an individual or thing” • A required attribute/property is expressed as a need or desire on an entity by some stakeholder. • An exhibited attribute/property is an attribute/property ascribed to an entity as a result of evaluating (for example measurement of) the entity. • The need for properties is motivated by their explanatory roles they have to fill. They describe phenomena of interest – There are no “absolute” properties

7. Functional vs. extra-functional attributes • Attribute/property • Functional – what a system is doing • Car: drive, brake, turn on right, light,…. • Computer: perform programs (software), connect to Internet… • Extra-functional properties - EFPs (aka non-functional, aka quality attributes) – How a system is performing • Car: speed, stability, safety, security, maintainability, energy consumption • Software: Performance, reliability, usability, security,…. • -- ilities.. • How can we describe EFPs? • How can we analyze EFPs? • How can we ensure EFPs? • How can we compute EFPs? • What are the limitations?

8. Some example of properties • Reusability, Configurability, Distributeability, Availability, Confidentiality, Integrity, Maintainability, Reliability, Safety, Security, Affordability, Accessibility, Administrability, Understandability, Generality, Operability, Simplicity, Mobility, Nomadicity, Hardware independence Software, independence, Accuracy, Footprint, Responsiveness, Scalability, Schedulability, Timeliness, CPU utilization, Latency, Transaction, Throughput, Concurrency, Efficiency, Flexibility, Changeability, Evolvability, Extensibility, Modifiability, Tailorability, Upgradeability, Expandability, Consistency, Adaptability, Composability, Interoperability, Openness, Heterogenity, Integrability, Audibility, Completeness, , Conciseness, Correctness, Testability, Traceability, Coherence, Analyzability, Modularity, …. Kazman, R., L. Bass, G. Abowd, M. Webb, “SAAM: A method for analyzing properties of software architectures,”Proceedings of the 16th International Conference on Software Engineering, 1994. Kazman et al, Toward Deriving Software Architectures from Quality Attributes, Technical Report CMU/SEI-94-TR-10, 1994. McCall J., Richards P., Walters G., Factors in Software Quality, Vols I,II,III', US Rome Air Development Center Reports, 1977. Bosch, J., P. Molin, “Software Architecture Design: Evaluation and Transformation,”Proceedings of the IEEE Conference and Workshop on Engineering of Computer-Based Systems, 1999.

9. Classification of properties • Different classification • Run-time properties – exhibits during the execution of the system • Reliability, safety, performance, robustness • Life cycle properties – visible in different phases of the system lifecycle • Maintainability, portability, reusability,… • Software from Components • Component properties • System properties • Emerging properties – those that do not exist on component level

10. Quality model in ISO 9126-I Example having source code reviews” (a Software development process quality) influences the source code in that “the number of not initialized variables” (an internal quality attribute of a software product) is minimized. This positively influences the reliability, of the system (an external quality attribute of a software product).

11. Existing Components General Concepts of the ISO/IEC 9126-1

12. Quality characteristics, sub-characteristics and attributes

13. ISO/IEC 9126-1 quality attributes

14. Other views – example: Dependability Avizienis, A.; Laprie, J.-C.; Randell, B.; Landwehr, C., “Basic concepts and taxonomy of dependable and secure computing”, IEEE Trans. Dependable Sec. Comput., Vol. 1, Issue 1, 2004 • Ability of a system to deliver service that can justifiably be trusted • Ability of a system to avoid failures that are more frequent or more severe than is acceptable to user(s) Related to • Trustworthiness (assurance that a system will perform as expected) • Survivability (capability to fulfill its mission in a timely manner) Safety-critical systems Dependability Mission-critical systems Business-critical systems Other systems – embedded systems - Desktop systems

15. Ability to Undergo repairs and evolutions Absence of improper system alternations Absence of unauthorized disclosure of information Absence of catastrophic consequences Continuity of services Readiness for usage Availability Reliability Safety Confidentiality Integrity Maintainability Dependability Attributes of Dependability

16. Availability Reliability Safety Confidentiality Integrity Maintainability Attributes Faults Errors Failures Dependability Threats Fault Prevention Fault Tolerance Fault Removal Fault Forecasting Means

17. Part II Predictability of composition of properties What do we know about properties compositions? What do we need to know to predict system properties from component properties?

18. The Challenges C1 C1 C3 Ic1 Ic1 Ic2 Component C2 Property P2 (AQ2) Component C1 Property P1 (QA1) C3 Ic2 Property P Is it possible (i.e. predict) to calculate P from P1 and P2? Is it possible to predict a quality attribute of a system from quality attributes of components?

19. Is it possible (i.e. predict) to calculate P from P1 and P2? Answer: It depends of the quality attribute (property). What if it is not possible? We can test and measure P (hopefully) But it can be time consuming It can be very expensive It can take more efforts to find P than (re)write the code In some cases it is not worth to se component-based approach

20. The main question • Which quality attributes are composable? • What are the prerequisites for a predictable composition? • The component properties themselves • System architecture • Particular usage profiles (how the components are used)? • The system and the system’s environment circumstances? Ivica Crnkovic, Magnus Larsson, Otto Preiss Concerning Predictability in Dependable Component-based Systems: Classification of Quality Attributes ArchitectingDependable Systems II, Springer LNCS 2005

21. Idea • Classification of quality attributes according to their composability • Related to the question • When we develop a components what do we need to know about its usage in the future systems? • When developed a system what do we need to know from the components, from the systems and from the system usage? Ivica Crnkovic, Magnus Larsson, Otto Preiss Concerning Predictability in Dependable Component-based Systems: Classification of Quality Attributes ArchitectingDependable Systems II, Springer LNCS 2005

22. Some definition first… Component Assembly – a set of components System System Usage System context

23. Different levels of knowledge about future component-based systems Component development (COTS type) Known: Architectural Framework, component model Unknown: system architecture, products, usage,.. Product line Known: domain, architectural framework, application skeleton,Variation (integration) points Unknown: Final products Open systems Known: similar to PLA,but integrators are not necessary known Final product ready to use (usage not necessary known) Final product in use What can we predict (or guarantee) about the system properties In each stage of development?

24. Classification • Directly composable properties.A property of an assembly which is a function of, and only of the same property of the components involved. • Architecture-related properties. A property of an assembly which is a function of the same property of the components and of the software architecture. • Derived (emerging) properties. A property of an assembly which depends on several different properties of the components. • Usage-depended properties. A property of an assembly which is determined by its usage profile. • System context properties. A property which is determined by other properties and by the state of the system environment.

25. Definition: A directly composable property of an assembly is a function of, and only of the same property of the components. • Consequence: to derive (predict) an assembly property it is not necessary to know anything about the system(s)

26. Example • “Physical characteristics” • Static memory • (the “function” can be much more complicated) • (the functions are determined by different factors, such as technologies)

27. Example (cont) • Dynamic memory – components with parameterized configurations/deployment paramentars

28. 2. Definition: An architecture-related property of an assembly is a function of the same property of the components and of the software architecture. • Consequence: System/assembly architecture must be known • Ok when building systems of particular class • (product-line architectures)

29. Example - distributed systems Client tier Web server tier Business logic tier Data tier Data access components Data Web server Business components Variability points Clients Yan L., Gorton I., Liu A., and Chen S., "Evaluating the scalability of enterprise javabeans technology", In Proceedings of 9th Asia-Pacific Software Engineer-ing Conference, IEEE, 2002.

30. 3. Definition: A derived property of an assembly is a property that depends on several different properties of the components. • Consequence: we must know different properties and their relations (might be quite complex)

31. A Output ports Input ports C1wcet1f1 C2wcet2f2 Example end-to-end deadline is a function of different component properties, such as worst case execution time (WCET) and execution period. fixed priority scheduling

32. Definition: AUsage-dependent property of an assembly is a property which is determined by its usage profile. Consequence: It is not enough to know which system will be built. It must be known how the system will be used

33. Example Reliability • the probability that a system will perform its intended function during a specified period of time under stated conditions. • Mean time between failure • How to calculate reliability for Software System? • Start from from a usage profile • Identify probability of the execution of components • Find out (measure) reliability of components • Calculate reliability of the system Ralf H. Reussner, Heinz W. Schmidt, Iman H. Poernomo, Reliability prediction for component-based software architectures The Journal of Systems and Software 66 (2003) 241–252 Claes Wohlin, Per Runeson: Certification of Software ComponentsIEEE Trans. Software Eng. 20(6): 494-499 (1994)

34. Can we predict reliability using existing usage profiles? Reuse problem: mapping system usage profile to component usage profile When the known (measured) properties values can be reused?

35. 5. Definition: A System Environment Context property is a property which is determined by other properties and by context of the system environment. • Consequence: It is not sufficient to know the systems and their usage, it is necessary to know particular systems and the context in which they are being performed

36. Example • safety property • related to the potential catastrophe • the same property may have different degrees of safety even for the same usage profile.

37. Summary - Classification • (DIR) - Directly composable properties.A property of an assembly which is a function of, and only of the same property of the components involved. • (ART) - Architecture-related properties. A property of an assembly which is a function of the same property of the components and of the software architecture. • (EMG) - Derived (emerging) properties. A property of an assembly which depends on several different properties of the components. • (USG) - Usage-depended properties. A property of an assembly which is determined by its usage profile. • (SYS) - System context properties. A property which is determined by other properties and by the state of the system environment. DIR – component context DIR – Architecture (assembly) context EMG – Architecture and other components context USG – Use context Sys – System (including external environemnt) context

38. Sources of information Ivica Crnkovic, Magnus Larsson Otto Preiss Concerning Predictability in Dependable Component-Based Systems: Classification of Quality Attributes, Architecting Dependable Systems III,, p pp. 257 – 278, Springer, LNCS 3549, Editor(s): R. de Lemos et al. (Eds.):, 2005 ISO/IEC, “Software engineering - Product quality - Part1: Quality model”, ISO/IEC, International, Standard 9126-1:2001(E). Ralf H. Reussner, Heinz W. Schmidt, Iman H. Poernomo, Reliability prediction for component-based software architectures The Journal of Systems and Software 66 (2003) 241–252 Claes Wohlin, Per Runeson: Certification of Software ComponentsIEEE Trans. Software Eng. 20(6): 494-499 (1994) Ivica Crnkovic and Magnus Larsson: Building Reliable Component-Based Software Systems Artech House Publishers, 2002, ISBN 1-58053-327-2 http://www.idt.mdh.se/cbse-book/