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Specification of Software Components

This graduate course outlines the specification of software components, focusing on their definitions, syntactic and semantic specifications, and methodologies related to Component-Based Software Engineering (CBSE). Key topics include UML class modeling, the importance of contractually specified interfaces, and the differentiation between syntactic and semantic aspects of component use. Additionally, practical examples and technologies like COM, CORBA, and JavaBeans are discussed, providing valuable insights for students and professionals involved in software development and component design.

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Specification of Software Components

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  1. Specification of Software Components Frank Lüders Mälardalen University, Dept. of Computer Engineering frank.luders@mdh.se CBSE – graduate course

  2. Outline • Introduction to Software Components and Specification • Introduction to UML Class Modeling • Syntactic Specification of Software Components • Semantic Specification of Software Components • Specification and CBSE Methodology • Conclusion CBSE – graduate course

  3. Software Components and Their Specification • 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 parts. • Internal components: same as above, except for the independent deployment and composition by third parts. • The specification of a software component is the key to its successful use as a part in a larger piece of software. CBSE – graduate course

  4. Different Types/Levels of Specification • Syntactic Specification • Specifies the syntax of using a component’s services • Technologies such as COM, CORBA, and JavaBeans • Semantic Specification • Also specifies the semantics of these services • State-of-the-art CBSE methodology • Extra-Functional Specification • Specifies properties besides a component’s services • A fairly new research area • NOT COVERED IN THIS TALK CBSE – graduate course

  5. Simple UML Class Models CBSE – graduate course

  6. UML Class Diagram CBSE – graduate course

  7. UML Class Diagram with Generalization CBSE – graduate course

  8. Aggregation and Composition CBSE – graduate course

  9. UML Metamodel CBSE – graduate course

  10. Syntactic Specification • A component implements a set of named interfaces and can require a set of interfaces implemented by others • An interface implements a set of named operations • An operation has a set of input and output parameterswith associated types • Variations: • A COM component implements a set of classes, each implementing a set of interfaces. 1 holds by association. • A JavaBean is a class with one interface which can be derived from (be a subtype of) several other interfaces. • An operation can have a return value. This can be viewed as an output parameter. CBSE – graduate course

  11. A Generic Model of Syntactic Specifications CBSE – graduate course

  12. Example: Specification of a COM component interface ISpellCheck : IUnknown { HRESULT check([in] BSTR *word, [out] bool *correct); }; interface ICustomSpellCheck : IUnknown { HRESULT add([in] BSTR *word); HRESULT remove([in] BSTR *word); }; library SpellCheckerLib { coclass SpellChecker { [default] interface ISpellCheck; interface ICustomSpellCheck; }; }; CBSE – graduate course

  13. Uses of Syntactic Specifications • Type checking of client code • Ensuring run-time interoperability • COM: binary standard for interfaces (vtables) • CORBA: mapping to programming languages • Ensuring syntactically safe substitution and evolution • Documentation - along with semantic descriptions CBSE – graduate course

  14. Semantic Specification • Extension of syntactic specification • A state model is associated with each interface • Operations have pre- and post-conditions • pre: state * in-parameters -> bool • post: state * state * in-parameters * out-parameters -> bool • Invariants on an interface’s state model • state -> bool • Intra-interface conditions for components • state1 * state2 * … -> bool CBSE – graduate course

  15. A Generic Model for Semantic Specifications CBSE – graduate course

  16. Example: UML Component Specification CBSE – graduate course

  17. Example: Object Constraint Language (OCL) context ISpellCheck::check(in word : String, out correct : Boolean) : HRESULT pre: word <> “” post: SUCCEEDED(result) implies correct= words->includes(word) context ICustomSpellCheck::add(in word : String) : HRESULT pre: word <> “” post: SUCCEEDED(result) implies words = words@pre->including (word) context SpellChecker ISpellCheck::words = ICustomSpellCheck::words CBSE – graduate course

  18. Uses of Semantic Specification • Tool support for component developers and users • Automatic correctness testing of components • Checking that client code satisfies pre-conditions • Ensuring semantically safe substitution and evolution • Liskov’s principle of substitution applies • Documentation – supplementary to natural language CBSE – graduate course

  19. Specification and CBSE Methodology • Methods using syntactic specification • “Normal” OO-methods, e.g. using UML • Directly supported by component technologies • Methods using semantic specification and UML/OCL • UML Components (Cheesman, Daniels, 2001) • Catalysis (D’Souza, Wills, 1998) • Methods using extra-functional specification • Ensemble (Wallnau, Stafford, 2001) CBSE – graduate course

  20. Conclusion • Syntactic vs. semantic specification • Syntactic specs is the only form in widespread use • The potential utility of semantic specs is much greater • UML may lead to wider use of semantic specification • Extra-functional specification • Many open issues • Will probably have great impact in the future CBSE – graduate course

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