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On Methodology from Domain to System Descriptions by Rolv Bræk NTNU Workshop on Philosophy and Applicablitiy of Formal Languages Geneve 15. September 2001. Topics. Methods and Methodology Languages for system modelling UML, MSC, SDL, ASN.1, TTCN Approaches Domain and Architecture issues.

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  1. On Methodologyfrom Domain to System DescriptionsbyRolv BrækNTNUWorkshop on Philosophy and Applicablitiy of Formal LanguagesGeneve 15. September 2001

  2. Topics • Methods and Methodology • Languagesfor system modellingUML, MSC, SDL, ASN.1, TTCN • Approaches • Domain and Architecture issues

  3. A methodology is a system of methods and principles. A method defines a systematic way to produce given results. Which is the way to quality results? Methods provide a kind of “roadmap” with guidelines and rules Methodology and Methods Themainresults of systems engineering are target systems and descriptions expressed using languages. Without any methods there would be no systems engineering discipline!

  4. Domain Model Domain descriptions Install Develop Manufacture System System descriptions The systems engineering cycle/spiral has needs quality = satisfaction of needs

  5. Domain descriptions System descriptions How to describe complex realities? Combine two golden rules: • Separation of concerns.Identify aspects that are as independent as possible and describe them separately. • Conceptual abstraction.Replace low level concepts representing technical detail by more abstract concepts better suited to describe and study some aspects, i.e. by some kind of model. First we separate domain from system; then what to separate? Can user aspects be separated from realisation aspects?

  6. The main separations Since the purpose of ICT systems is to provide functionality(perform logical behaviourand handle information); and the functionality may be realised in many ways: • separatefunctionalityfromrealisation • describe thedeploymentmapping separately

  7. Functionality Is a conceptual abstraction intended to describes logical behaviour and information as clearly as possible It should enable users and developers: • to communicate precisely • to establish a common understanding • to ensure that the descriptions of functionality correctly represents the existing domain and/or the system being developed It provides a view where the system may be seen as a whole, independently of realisation and technology Is normally described in terms of structures of active and passive objects with associated object behaviours

  8. Realisation Is a precise technical definition of the realisation in terms of the technologies used, such as mechanics, electronics and software Is necessary to actually produce a working system The choice of realisation depends on what properties are desired from the realisation itself (often called non-functional properties)

  9. Deployment and configuration descriptions Describes aspects that come in addition to the functionality, such as distribution, hardware/software allocation and use of middleware and defines a mapping between functionality and realisation by: • describing the realisation (the physical system) on a high level • identifying the technologies used • describing how and where the functionality is realised • describes configurations Serves together with functionality as the main documentation. configuration data; priorities; versions; etc.

  10. Enterprise RM-ODP viewpoints • Information • Computation • Engineering • Technology

  11. Objects and properties

  12. context specification content design General description pattern properties objects ••• ••• ••• ••• component types (follow same pattern) •••

  13. Coverage of the ITU-T languages and UML

  14. Two main approaches: • Elaboration approach: the functionality description is incomplete and expressed using languages with incomplete semantics => the realisation description ends up as the only complete view of the system and the functionality description is not maintained Most UML use including the Rational Unified Process, RUP, follows the elaboration approach • Translation approach: the functionality description is complete and expressed using languages with well-defined and realistic semantics => the functionality description is valid for the realisation, serve as documentation and is maintained Realisation is by (manual or automatic) translation of the functionality description. Deployment is orthogonal to the functionality (using the principle of distribution transparency). Most SDL use follow this approach.

  15. Quality assurance Techniques: • Corrective techniques: defect detection, with subsequent correction,e.g. formal verification, simulation, testing and inspection. • Constructive techniques: defect avoidance, i.e. to avoid introducing errors in the first place, e.g. synthesis and automatic program generation, languages and methods that help to improve understanding and communication. Aspects • Quality of functionality: related to the main purposes, i.e. the needs of the domain. • Quality of realisation, i.e. way the functionality is realised. the most effective separated in the translation approach

  16. Which is your preferred approach? Implementation oriented The UML approach Design oriented The ITU-T approach

  17. Languages for functionality should • Support human comprehension so that human beings may fully understand and communicate precisely about the functionality => build on concepts that are suitable, well defined, and easy to understand. • Provide analytical possibilities so that one may reason about behaviours in order to compare systems, to validate interfaces, and to verify properties. => have a semantic foundation suitable for analysis. • Be realistic. Although overlooked in many cases, this requirement is essential for two main reasons: • That it shall be possible to implement the functionality • That the description of the functionality can serve as valid documentation of the real system. => build on concepts that can be effectively realised in the real world.

  18. Macro Methodology

  19. Develop system

  20. Adressed by SDL, MSC, TTCN and ASN.1 Adressed by CHILL Features of existing telematics systems Functionality: • Highly parallel behaviour • Time dependency/real time • Sessions – stateful behaviour • Object interaction orientation • Robust • Highly complex • Contention for shared resources • A lot of operation and maintenance support • Adaptability to new contexts and services (partly on-the-fly) Realisation: • Physical distribution • High performance • Scalability • Replication/fault tolerance Quality first!

  21. Addressed by UML Addressed by combining and aligning UML and ITU-T languages Some trends Functionality • More focus on classes, associations and inheritance • More data and object-action-orientation • Horizontal integration/interfacing with legacy and 3rd party • More hacker mentality (and quality problems) • The classical features remain unchanged! Realisation/technology • IP connectivity • Web based access • Middleware • 3rd party service platforms • More Java and Mobile code functionality before quality

  22. Is it true that: • specifications describe implementations? • no – they specify properties and functionality, i.e. another view • specification languages are modeling approaches? • no – they are just languages, but may be used for modeling • specification languages are description techniques? • yes/no – they may be used to describe a valid view

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