1. Software Product Families. Generative Programming Main text: Ian Sommerville, Software Engineering, 8 th edition, chapter 18 Additional readings: K. Czarnecki. Overview of Generative Software Development. In J.-P. Banâtre et al. (Eds.): Unconventional Programming Paradigms (UPP), LNCS 3566, pp. 313–328, 2005. http://www.swen.uwaterloo.ca/~kczarnec/gsdoverview.pdfhttp://www.swen.uwaterloo.ca/~kczarnec/gsdoverview.pdf Czarnecki and Eisenecker, Components and generative programming. ESEC/FSE 1999. http://www.prakinf.tu-ilmenau.de/~czarn/esec99/esec99.pdfhttp://www.prakinf.tu-ilmenau.de/~czarn/esec99/esec99.pdf

2. Review: Reuse Taxonomy – what, how, where to reuse ? From [Prieto-Diaz91]

3. Reuse – by substance Classification of reuse according to the essence of items to be reused: – Ideas, concepts: Reuse of abstract concepts – sharing “wisedom” General solutions to a class of problems: algorithms – Artifacts, components Reuse of software parts – Processes, procedures, skills Reusable processes – needs more formalization of software development procedures Procedure reuse – means also the informal reuse of skills

4. Reuse – by scope Classification of reuse according to the form and extent of reuse: – Vertical: reuse within the same domain or application area Goal: to build generic models for families of systems that can be used as templates for building new system in that domain Needs: effort in domain analysis and domain modelling – Horizontal: reuse of generic parts in different applications Example: scientific subrutines Needs: packaging and presentation of parts; cataloging and classification standards for parts;

5. Reuse – by technique Classification of reuse according to the the approach used to implement reuse: – Compositional Uses existing components as building blocks for new systems – Generative Reuse at the specification level by means of application or code generators

6. Reuse – by product Classification of reuse according to the work products that are reused: – Source code – Design – Specifications – Objects – Text – Architectures

7. The reuse landscape Although reuse is often simply thought of as the reuse of system components, there are many different approaches to reuse that may be used. Reuse is possible at a range of levels from simple functions to complete application systems. The reuse landscape covers the range of possible reuse techniques.

8. The reuse landscape Fig. 18.3 from [Sommerville] Design patterns Component-based development Component frameworks Service-oriented systems COTS integration Application product lines Legacy system wrapping Program libraries Program generators Aspect-oriented software development Configurable vertical applications

9. Reuse approaches Fig. 18.4 from [Sommerville]

10. Reuse approaches (cont)

11. What to reuse Software building blocks – Who reuses: Third party reuse: COTS Intra-organizational: Software product lines Concept reuse – Concepts are abstract, the reuse process includes an instantiation activity – How: Manually: Design patterns. Automatic: Program generators.

12. Software product lines Software product lines or application families are applications with generic functionality that can be adapted and configured for use in a specific context. All members of the family share a common core: – The application-specific architecture – A set of core components Adaptation (creation of individual family members) may involve: – Component and system configuration; – Adding new components to the system; – Selecting from a library of existing components; – Modifying components to meet new requirements.

13. Specialisation in a product line Platform specialisation – Different versions of the application are developed for different platforms. Environment specialisation – Different versions of the application are created to handle different operating environments e.g. different types of communication equipment. Functional specialisation – Different versions of the application are created for customers with different requirements. Ex: a library automation system for a public library or a university library. Process specialisation – Different versions of the application are created to support different business processes.

14. Product line configuration Software product lines are designed to be reconfigured. Reconfiguration: – Adding or removing components – Defining parameters and constraints for components – Including knowledge of business processes Software product lines can be configured at 2 points in the development process: – Deployment time configuration A generic system is configured by embedding knowledge of the customer’s requirements and business processes. The software itself is not changed. – Design time configuration A common generic code is adapted and changed according to the requirements of particular customers.

15. Example: ERP systems An Enterprise Resource Planning (ERP) system is a generic system that supports common business processes such as ordering and invoicing, manufacturing, etc. These are very widely used in large companies - they represent probably the most common form of software reuse. The generic core is adapted by including modules and by incorporating knowledge of business processes and rules. The configuration process for these systems involves gathering detailed information about the customer’s business and business processes and then embedding this information in a configuration database. This often requires detailed knowledge of configuration notations and tools and is usually carried out by consultants working alongside system customers.

16. Configuration of an ERP System Fig. 18.12 from [Sommerville]

17. Design time configuration Software product lines that are configured at design time are instantiations of generic application architectures (see Chapter 13). Involves changing and extending the source code of the core system Offers greater flexibility than deployment-time configuration Generic products usually emerge after experience with specific products.

18. Product line architectures The decision to design a generic product line becomes explicit at a point, otherwise changes may corrupt the application structure Architectures must be structured in such a way to separate different sub-systems and to allow them to be modified. The architecture should also separate entities and their descriptions and the higher levels in the system access entities through descriptions rather than directly.

19. Product line: Vehicle despatching A specialised resource management system where the aim is to allocate resources (vehicles) to handle incidents. Versions for: police, fire service, ambulance service Adaptations include: – At the UI level, there are components for operator display and communications; – At the I/O management level, there are components that handle authentication, reporting and route planning; – At the resource management level, there are components for vehicle location and despatch, managing vehicle status and incident logging; – The database includes equipment, vehicle and map databases.

20. A vehicle despatching system Fig. 18.14 from [Sommerville]

21. The vehicle despatching system To create a specific version of this system, you may have to modify individual components. For example, the police have a large number of vehicles but a small number of vehicle types, whereas the fire service has many types of specialised vehicles, so a different vehicle database structure may need to be incorporated into the system.

22. Product instance development Fig. 18.15 from [Sommerville]

23. Product instance development Elicit stakeholder requirements – Use existing family member as a prototype Choose closest-fit family member – Find the family member that best meets the requirements Re-negotiate requirements – Adapt requirements as necessary to capabilities of the software Adapt existing system – Develop new modules and make changes for family member Deliver new family member – Document key features for further member development

24. Concept reuse When you reuse program or design components, you have to follow the detailed design decisions made by the original developer of the component. – This may limit the opportunities for reuse. One way around is to reuse abstract designs (concepts) that do not include implementation details – You must implement the abstract design for your application – Examples of reusable concepts: algorithms, abstract data types, design patterns Main approaches to concept reuse are: – Design patterns – Generative programming

25. Generator-based reuse Concept reuse through patterns: – relies on describing the concept in an abstract way and leaving it up to the software developer to create an implementation Generator-based reuse: – Program generators involve the reuse of standard patterns and algorithms. – These are embedded in the generator and parameterised by user commands. A program is then automatically generated. – Generator-based reuse is possible when domain abstractions and their mapping to executable code can be identified. – A domain specific language is used to compose and control these abstractions.

26. Reuse through program generation Fig. 18.8 from [Sommerville]

27. Types of program generators Generator-based reuse takes advantage of the fact that applications in the same domain have common architectures and carry out similar functions Areas of use for program generator – Application generators for business data processing Systems follow an input-process-output model Usually include operations as data verification and report generation – generic components – Parser and lexical analyser generators for language processing (examples: lex, yacc); input=the grammar output=the parser program – Code generators in CASE tools; input=design diagrams output=program implementing the design

28. Generator-based reuse Disadvantages: – Generator-based reuse has a high initial cost in defining and implementing the domain concepts and language – its applicability is limited to a relatively small number of application domains. Advantages: – It is easier for end-users to develop programs using generators compared to other component-based approaches to reuse. Future: – Generative programming

29. Generative programming Combines program generation with component-based development Applicable for System-family engineering (also known as software product-line engineering) exploits the commonalities among systems from a given problem domain while managing the variabilities among them in a systematic way Generative software development is a system-family approach, which focuses on automating the creation of system-family members: a given system can be automatically generated from a specification written in one or more textual or graphical domain-specific languages

30. Spectrum of generative approaches from [Czarnecki]

31. COTS product reuse is concerned with the reuse of large, off-the-shelf systems. Software product lines are related applications developed around a common core of shared functionality. Program generators are also concerned with software reuse - the reusable concepts are embedded in a generator system. Key points