1. Software Models (Cont.) 9/22/2015ICS 413 – Software Engineering1 -Component-based software engineering -Formal Development Model

2. Objectives To explain that CBSE is concerned with developing standardised components and composing these into applications To describe components and component models To show the principal activities in the CBSE process To discuss approaches to component composition and problems that may arise 9/22/2015ICS 413 – Software Engineering2

3. Topics covered Components and component models The CBSE process Component composition 9/22/2015ICS 413 – Software Engineering3

4. Component-based development Component-based software engineering (CBSE) is an approach to software development that relies on software reuse. It emerged from the failure of object-oriented development to support effective reuse. Single object classes are too detailed and specific. Components are more abstract than object classes and can be considered to be stand- alone service providers. 9/22/2015ICS 413 – Software Engineering4

5. CBSE essentials Independent components specified by their interfaces. Component standards to facilitate component integration. Middleware that provides support for component inter-operability. A development process that is geared to reuse. 9/22/2015ICS 413 – Software Engineering5

6. CBSE and design principles Apart from the benefits of reuse, CBSE is based on sound software engineering design principles: – Components are independent so do not interfere with each other; – Component implementations are hidden; – Communication is through well-defined interfaces; – Component platforms are shared and reduce development costs. 9/22/2015ICS 413 – Software Engineering6

7. CBSE problems Component trustworthiness - how can a component with no available source code be trusted? Component certification - who will certify the quality of components? Emergent property prediction - how can the emergent properties of component compositions be predicted? Requirements trade-offs - how do we do trade-off analysis between the features of one component and another? 9/22/2015ICS 413 – Software Engineering7

8. Components Components provide a service without regard to where the component is executing or its programming language – A component is an independent executable entity that can be made up of one or more executable objects; – The component interface is published and all interactions are through the published interface; 9/22/2015ICS 413 – Software Engineering8

9. Component definitions Councill and Heinmann: – A software component is a software element that conforms to a component model and can be independently deployed and composed without modification according to a composition standard. Szyperski: – A software component is a unit of composition with contractually specified interfaces and explicit context dependencies only. A software component can be deployed independently and is subject to composition by third-parties. 9/22/2015ICS 413 – Software Engineering9

10. Component as a service provider The component is an independent, executable entity. It does not have to be compiled before it is used with other components. The services offered by a component are made available through an interface and all component interactions take place through that interface. 9/22/2015ICS 413 – Software Engineering10

11. Component characteristics 1 9/22/2015ICS 413 – Software Engineering11

12. Component characteristics 2 9/22/2015ICS 413 – Software Engineering12

13. Formal Specification 9/22/2015ICS 413 – Software Engineering13

14. Objectives To explain why formal specification techniques help discover problems in system requirements 9/22/2015ICS 413 – Software Engineering14

15. Topics covered Formal specification in the software process 9/22/2015ICS 413 – Software Engineering15

16. Formal methods Formal specification is part of a more general collection of techniques that are known as ‘formal methods’. These are all based on mathematical representation and analysis of software. Formal methods include – Formal specification; – Specification analysis and proof; – Transformational development; – Program verification. 9/22/2015ICS 413 – Software Engineering16

17. Acceptance of formal methods Formal methods have not become mainstream software development techniques as was once predicted – Other software engineering techniques have been successful at increasing system quality. Hence the need for formal methods has been reduced; – Market changes have made time-to-market rather than software with a low error count the key factor. Formal methods do not reduce time to market; – The scope of formal methods is limited. They are not well-suited to specifying and analysing user interfaces and user interaction; – Formal methods are still hard to scale up to large systems. 9/22/2015ICS 413 – Software Engineering17

18. Use of formal methods The principal benefits of formal methods are in reducing the number of faults in systems. Consequently, their main area of applicability is in critical systems engineering. There have been several successful projects where formal methods have been used in this area. In this area, the use of formal methods is most likely to be cost-effective because high system failure costs must be avoided. 9/22/2015ICS 413 – Software Engineering18

19. Specification in the software process Specification and design are inextricably intermingled. Architectural design is essential to structure a specification and the specification process. Formal specifications are expressed in a mathematical notation with precisely defined vocabulary, syntax and semantics. 9/22/2015ICS 413 – Software Engineering19

20. Specification and design 9/22/2015ICS 413 – Software Engineering20

21. Specification in the software process 9/22/2015ICS 413 – Software Engineering21

22. Use of formal specification Formal specification involves investing more effort in the early phases of software development. This reduces requirements errors as it forces a detailed analysis of the requirements. Incompleteness and inconsistencies can be discovered and resolved. Hence, savings as made as the amount of rework due to requirements problems is reduced. 9/22/2015ICS 413 – Software Engineering22

23. Cost profile The use of formal specification means that the cost profile of a project changes – There are greater up front costs as more time and effort are spent developing the specification; – However, implementation and validation costs should be reduced as the specification process reduces errors and ambiguities in the requirements. 9/22/2015ICS 413 – Software Engineering23

24. Development costs with formal specification 9/22/2015ICS 413 – Software Engineering24

25. Specification techniques Algebraic specification – The system is specified in terms of its operations and their relationships. Model-based specification – The system is specified in terms of a state model that is constructed using mathematical constructs such as sets and sequences. Operations are defined by modifications to the system’s state. 9/22/2015ICS 413 – Software Engineering25

26. Formal specification languages 9/22/2015ICS 413 – Software Engineering26