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Components, Component Models and Reuse

Components, Component Models and Reuse. ICS 123 Richard N. Taylor and Eric M. Dashofy UC Irvine http://www.isr.uci.edu/classes/ics123s02/. * with very special thanks to David S. Rosenblum for the use of his materials. What Is Reuse? (I).

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Components, Component Models and Reuse

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  1. Components, Component Models and Reuse ICS 123 Richard N. Taylor and Eric M. Dashofy UC Irvine http://www.isr.uci.edu/classes/ics123s02/ * with very special thanks to David S. Rosenblum for the use of his materials..

  2. What Is Reuse? (I) • Develop systems of components of a reasonable size and reuse them • Further use or repeated use of a component • Adapting components for use outside their original context • Extend the idea beyond code to other development artifacts • Goals of reuse are primarily economic • Save cost/time/effort of redundant work, increase productivity • Decrease time to market • Improve systems by reusing both the artifact and the underlying engineering experience • Economic goals achieved only when units of reuse reach critical mass in size, capability and uniformity

  3. What Is Reuse? (II) • Idea originally due to Doug McIlroy “Mass Produced Software Components”, 1968 NATO Conference on Software Engineering • Reusable components, component libraries • Named as a potential “silver bullet” by Fred Brooks (1987) • A lot of research interest in the 1980s and 1990s • Technical and managerial barriers have prevented widespread success with reuse and with reuse-oriented technologies • This led McIlroy to believe he had been wrong!

  4. What Is Reuse? (III) • The term reuse is a misnomer • No other engineering discipline uses the term • Systematic design and use of standard components is accepted practice in other engineering disciplines • The term will (eventually) become obsolete • The important ideas behind reuse are centered on the notion of components • Design of components for use in multiple contexts • Design of families of related components • Design of components with standardized packaging

  5. Review:Architectural Components • A component is an architectural building block that is … • A unit of computation or a data store, with an interface specifying the services it provides • A unit of deployment • A unit of reuse

  6. The Difference Between Components and Objects • Objects have a unique identity • Objects have a persistent state • Objects are instances of a class, with classes arranged in hierarchies according to inheritance relationships (object-oriented design and programming) • Components may contain many classes and class instances • Objects can be passed as parameters in methods • Components vary more dramatically in size

  7. Component Packaging Standards • Models and tools for building, packaging and interconnecting software components • Called by many different names • Component standards • Component models • Distributed component platforms • … • Our focus in this course will be on the C2component model, although we will discuss others

  8. Key Goals of a Component Standard • Language independence • Interchangeability of Components • Requires separation of interface from implementation • Requires standardized interface definition language (IDL) • Current IDLs primarily support syntactic interface specification • Limited support for specification of semantics: strong typing • Customizability of Components • Components are tailored for application use in well-defined, predetermined ways • Compositionality of Components • Easy formation of larger-grained components and whole applications

  9. Important Features of Component Standards • Component interfaces • Metadata • Integrated development environments (IDEs) • Distributed server components

  10. Component Interfaces • Define facilities for interoperation with other components • Properties/attributes/data members • Entities forming component state • Methods/operations/function members • Entities allowing access and changes to component state • Events • Component response to internal or external stimuli • Event consumers (other components) register their interest with a component that generates events

  11. Component Metadata • Component data for the use of other components, rather than for the direct support of the component’s functionality • Class name, interface elements, resources, visual representation, etc. • Some component standards also support metaoperations • Supports discovery of a component’s capabilities, especially at runtime • Encapsulated in separate components or metaclasses • Often called “introspection” or “reflection” • Introspection is a misnomer—implies component looking at itself • Reflection is a better term—externally available information reflecting internal capabilities

  12. Integrated Development Environments (IDEs) • Application development based on direct manipulation of visually rendered components • Drag-and-drop composition • Color-coded syntax source code highlighting and checking • Integrated source code editors, compilers, debuggers • Class, object, component repositories • Configuration management capabilities • Versions • Configurations • Teams

  13. Distributed Server Components • Support for “enterprise-wide” distribution and management of shared multi-user applications • Protocols for communication with remote components • Transaction services for shared data components • Component and resource naming services • Security services • System management, monitoring, administration services • This is the focus of distributed object technology and other kinds of client/server middleware

  14. Component Frameworks • Component-based implementation of an important design pattern or architectural style, tailored to specific application domain • Provides guidance for application construction • Provides base architecture that can be tailored for specific application • Well-known example: Microsoft Foundation Classes (MFC) • Implementation of Model-View-Controller (MVC) style for GUI development • Supported by powerful IDE (Visual C++/Visual J++) • Application generation • Development wizards

  15. Leading Creators of Component Standards • Microsoft • OLE: Object Linking and Embedding • COM: Component Object Model (component model underlying OLE) • ActiveX (enhancement and generalization of OLE) • DCOM: Distributed COM • SOAP: Simple Object Access Protocol (Is this a component standard?) • Sun Microsystems • JavaBeans • Enterprise JavaBeans • Jini • Object Management Group (OMG) • OMA: Object Management Architecture • CORBA: Common Object Request Broker Architecture (part of OMA) • UML: Unified Modeling Language • World Wide Web Consortium (W3C) • XML (Is this a component standard?)

  16. Who Will Win? • Who knows? • Microsoft tends to win everything • But there is a lot of industry buy-in for Java and related technologies • OMG stays afloat by reacting to whatever Microsoft and Sun do • What if there isn’t a winner? • Interoperability between component standards is always possible • Bridges • Adapters • Wrappers • Etc.

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