Software Engineering with Reusable Components

1. Software Engineeringwith Reusable Components RiSE’s Seminars Sametinger’s book :: Chapters 6 and 7 Fred Durão

2. Summary • Software Components (Chapter 6) • Component Definition • Component Interfaces • Component Platforms • Component Composition (Chapter 7) • Forms of Composition • Forms of Interoperation • Composition Mismatches

3. Software Components

4. Software Components :: Chapter 6 History • In 1969 McIlroy envisioned an industry of reusable software components [McI76]. • In 1982 Wasserman and Gutz saw the programmer of the future working with “standard components…” • Today we are making that dreams becaming true.

5. Software Components :: Chapter 6 Component Definitions • Reusable software components are self-contained, clearly identifiable artefacts that describes and/or perform specific functions and have clear interfaces, appropriate documentation and a defined reuse status. • Self-Contained • Identification • Functionality • Interfaces • Documentation • Reuse Status

6. Software Components :: Chapter 6 Related Work • [HP88] describes a component as “logical part of a system or program” • [MDK96] defines a component as “…any unit that provides a relatively independent piece that is used in combination with a number of components in different configuration” • [HC91] use the term software component “to mean any type of software resource that may be reused…”

7. Software Components :: Chapter 6 Component Interface • Components are not completely independent of other components and of their environments; • Many components are implemented in a specific language programming; • Interface determines how a component can be reused and interconnected; • It defines an operation or a set of operations that is available for a component; • It provides abstraction and hides the details of implementation.

8. Software Components :: Chapter 6 Component Interface • Interfaces are crucial to composition of components; • The components can be connected by the interfaces; • Multiple Interfaces; • Useful to structure of complex functionality. • Single Interface; • Useful to structure of specific functionality

9. Software Components :: Chapter 6 Interface Types • Data interface • Data Handling; • Programming interface • API’s; • User interface • Require interaction from the user - scripts • Command language interface • Provide communication mechanisms between interactive programs

10. Software Components :: Chapter 6 Component Platforms • Components generally require different platforms. • Platforms can be described as: • Run-time systems; • Operating systems; • Window systems; • Libraries; • Components are the more reusable the less platforms they depend on and more portable are these platforms;

11. Software Components :: Chapter 6 Platforms Categories • Execution Platforms • Necessary in order to execute a component. • Hardware, Operating System, Programming Systems, Virtual Machines. • Composition Platforms • Necessary for components that do not run their own but have to be integrated with other components to form a executable program. • e.g. compilers, libraries, data storage and GUI (Win 95).

12. Software Components :: Chapter 6 Component and Platforms Dependencies • Two components or more can work together only if they: • share the same execution platform or; • use different execution platform but common composition platform. • The relationship between component and platform is responsible for level of the portability. • The portability of a component correlates with its reusability.

13. Software Components :: Chapter 6 Open Systems • The less platform dependencies a component has the more portable and reusable is a component. • Advantages: • Composability • Two components can work through well-defined interfaces. • Component portability • Components developed on one platform should be usable on different platforms with no or minimal change. • User portability • Ease of switching among user interfaces of different components • Integration • The ease case which a component can be used by other components

14. Software Components :: Chapter 6 Open Systems • Standards are crucial for open system • e.g. a component might execute under Unix, yet be restrict to certain Unix implementation. So all Unix variations should implement standard interfaces.

15. Software Components :: Chapter 6 Design Patterns • Are not considered software components; • Can be regarded as platforms of component development or application “frameworks”;

16. Component Composition

17. Component Composition :: Chapter 7 Component Composition • [ND95] defines software composition as “the process of constructing applications by interconnecting software components through their plug[s]”. • [dM95] defines component composition as “communication between components through their interfaces”

18. Component Composition :: Chapter 7 The two basic forms: • Internal Composition • Integrated into a system and become an inherent part of the system; • e.g. Source code or executable code; • External Composition, • Independent; • Run on their own; • Can be used as complete programs by themselves; • e.g. Web Services Components

19. Component Composition :: Chapter 7 Component Distinction • [ND95] • Functional Composition; • Blackboard Composition; • Composition by extension; • [NM95] • Macro Expansion; • to compensate lacking of language programming features. • High Order Functional; • Binding of communication channels;

20. Component Composition :: Chapter 7 Textual Composition • Best represented by Macros; • Macros are code extensions; • Composition by textual replacement; • There is no interface defined, can be arbitrary chosen; • Use more C and C++ programming language; • e.g. Part of a function or expression;

21. Component Composition :: Chapter 7 Functional Composition • Most widespread mechanism; • Most programming languages offer this mechanism; • e.g. libraries and packages; • Disvantages: • Usually written in the same language; • Solution: e.g. Web Services or Cross Platforms Languages. • Remote procedure Call • Distributed computing; • Provide some abstraction

22. Component Composition :: Chapter 7 Modular Composition • Collection of data structures and/or functions; • Important abstraction mechanism • Data encapsulation and information hiding. • Avoid implicit interfaces; • e.g. Ada Math Advantage (consisting of over a hundred frequently used mathematical and utility components);

23. Component Composition :: Chapter 7 Object-Oriented Composition • Use of inheritance, polymorphism, dynamic-binding and encapsulation; • Advantages: • Reuse of existing source code; • Adaptation of programs to work in similar but different situations; • Extraction of commonalties from different classes, and • Organization of objects into hierarchies • More flexibility; • Increases the reuse potential of existing code.

24. Component Composition :: Chapter 7 Source Code Parameterization • In order to make source code adaptable and thus reusable; • Is a textual composition technique.

25. Component Composition :: Chapter 7 Distributed Computing • Modules of components exchange messages over communications network or by sharing memory; • Advantages: • High speed; • High availability; • Functional specialization; • Parallelism;

26. Component Composition :: Chapter 7 Object Models: Components running on different machines and platforms • Corba • Use a OO paradigm and hide programming language and operating system differences. • Interface Definition Language (IDL) • Describe a common interface component. • Object Request Broker • Channel of communication between components in different platforms.

27. Component Composition :: Chapter 7 Compound Documents: Reducing the complexity of mega-applications • A lean of software components that work cooperatively rather than to develop monolithic mega-applications • The end user partly takes the role of a software developer • Increase of software reuse • Examples: • OpenDoc • Ms/OLE

28. Component Composition :: Chapter 7 Component Application • Integrated Components • Open Platform Composition CORBA

29. Component Composition :: Chapter 7 Forms of Interoperation • Interoperability is the ability of software components to communicate and cooperate despite differences in language, interface and execution platform [Kon95, Weg95]. • Successful composition does not imply in successful interoperation; • Integration mechanisms: • Control Integration; • Accomplished by means of exchange message; • Data Integration; • Accomplished by means of database or file system;

30. Component Composition :: Chapter 7 Categories of Interoperation : Exchanging Data • No control • Components share data without directly communication with each other • Static Control Components share data without directly communication with each other • The sending component has a fixed received component; • Dynamic Control • Function call with dynamic binding. More flexibility. • Broadcast Control • Components may share separate data.

31. Component Composition :: Chapter 7 Composition Mismatches • Component composition is compared to eletrictal appliances...standardization ends at in the country´s border. • [Sha95] listed ad-hoc tricks to connect mismatched components: • Component Modifications – decreases the potencial reuse. • Parallel component version – e.g. Unix Operation, problem: short life. • Adapters / Wrappers – avoid direct modifications of the component. • Components with converters – able to read something and write several formats. • Multilingual components – can be executed on various plataforms. • Intermediate forms – useful when many components are involved.

32. Component Composition :: Chapter 7 Interface Bridging and Standardization • The two major mechanisms for the solving of component mismatches. • Interface transformation language are used to express how on offered interface can be transformed to the requested interface[Kon95]. • Interface definition language are used to express specific interfaces in a programming language independent way[Kon95]. • e.g. Object Models like Corba [mz95] provide interface standardization.

33. References • SAMETINGER, J. Software Engineering with Reusable Components. Springer-Verlag, 1997.