Mälardalen University (MdH)

1. Component-based Approach and Dependable SystemsConcerning Predictability of Component-basedSystems: Classification of 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 • Department of Computer Science and electronics (IDE) • Real-Time Systems Design Lab • Computer Architecture Lab • Computer Science Lab • Software Engineering Lab • Intelligent sensors Lab Medical Equipment

4. 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/

5. Outline • Introduction • Why CBD • Parti I • Properties (Quality attributes) • Part II • Composability vs. predictability of Quality Attributes • Classification of Quality attributes

6. What is Component-based approach? • Building systems from (existing) software components • Providing support for the development of systems as assemblies of components • Supporting the development of components as reusable units • Facilitating the maintenance and evolution of systems by customizing and replacing their components • Separation of building components from building systems

7. Why component-based approach? • Primary a concern of business and life-cycle factors • Costs, Time-to-market • Flexibility • Understandability, maintainability • Reuse of already existing software • Higher abstraction level for functional properties • To less degree a concern of non-functional properties • The requirements that must be fulfilled also with this approach • Sometimes more difficult to achieve • Might be a reason that component-based approach is less (or not) feasible

8. The main question • CBD has shown to be successful in many domains (desktop, distributed web-based applications...) • What are the benefits and what are the drawbacks of CBD for particular domains? • Benefits /drawbacks for dependable (embedded) systems? • What are the primary concerns and requirements of particular domains? • Can CBD contribute in providing solutions that meet these requirements/concerns? • Yes • No • Make it more difficult

9. Part IComponents and system properties What are properties?

10. 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

11. 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.

12. Classification of properties • Different classification • Run-time properties • Life cycle properties • Run time • Reliability, safety, performance, robustness • Life cycle • Maintainability, portability, reusability,… • CBSE • Component properties • System properties • Emerging properties

13. 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).

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

15. ISO/IEC 9126-1 quality attributes

16. 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

17. 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

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

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

20. Main concern: Composability and predictability ofextra-functional properties • Classification in respect to: • to ability to predict system properties from component properties • (ability to verify the predictability) Ivica Crnkovic, Magnus Larsson, Otto Preiss Concerning Predictability in Dependable Component-based Systems: Classification of Quality Attributes Architecting Dependable Systems II, Springer LNCS 2005

21. Some definitions first… Component Assembly – a set of components System System Usage System context

22. 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?

23. 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.

24. 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)

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

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

27. 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)

28. 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.

29. 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)

30. 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

31. 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

32. 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)

33. 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?

34. 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

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

36. 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

37. Composition Combination of Different Types of Properties • Classification should be • Complete • Orthogonal • The shown classification is an idealization • Some properties will be of combination of different types

39. Experiment • Questionnaire • A set of defined properties • Grouped in different “sets of concerns” • Following ISO 9126 standard and Dependability classification • Assignment: • Classify the proposed properties

40. Questionnaire Questionnaire – instructions For each property (Quality attribute) in the table ask the following questions: • (Directly composable attributes) Is it possible to analyze this assembly quality attribute given the same quality attribute of the components involved? b. (Architecture Related attributes) Is it possible to analyze this assembly quality attribute given the assembly software architecture and the same quality attribute of the components involved? c. (Derived attributes) Is it possible to analyze this assembly quality attribute from several different component attributes of the components involved? d. (Usage-dependent attributes) Is it necessary to know the usage profile of the assembly to analyze this quality attribute? e. (System environment context dependent attributes) Is it necessary to have system environment information to analyze this quality attribute? Answer each question with: 0 = No, 1 = yes, 2 = yes, significantly There is also a question where you can indicate the confidence in your answers for each attribute. (scale 1 to 5) Please fill in answers on all attributes and indicate with the confidence of your selection 1= little confidence 5=high confidence

41. Survey -Distribution of attribute classification

42. Level of agreement of the participants for the classification

43. Conclusion • “Return of investment” for component-based approach depends also on predictability and assurance of quality attributes • Composability of different quality attributes is different • The ability of predicting system properties from component properties vary – from pure component properties to properties of systems exhibited differently in different context • This limits the prediction ability of CB system’s behaviour