1 / 22

Course structure

Course structure. 1: Component software principles 2: Javabeans 3: COM (DCOM/COM+/OLE/ActiveX) 4: CORBA, more ActiveX, comparison. Session 1 Outline. Software components definitions, advantages old reuse: Issues in component software interfaces, interface descriptions

robyn
Download Presentation

Course structure

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Course structure 1: Component software principles 2: Javabeans 3: COM (DCOM/COM+/OLE/ActiveX) 4: CORBA, more ActiveX, comparison MIT IAP 1999

  2. Session 1 Outline • Software components • definitions, advantages • old reuse: • Issues in component software • interfaces, interface descriptions • transparent distribution: proxies & stubs • persistence • naming, versioning • Demonstration MIT IAP 1999

  3. Component based software Software component • a software building block “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.” [Szyperski 97] MIT IAP 1999

  4. Minimalist component [Orfali, Harkey] • marketable entity: self-contained, shrink-wrapped, binary • not a complete application • usable in unpredicted combinations: ‘plug&play’ • well-specified interface • interoperable: invoked across processes, machines, networks, languages, OS, tools • extended object: supports encapsulation, inheritance, polymorphism MIT IAP 1999

  5. Security Licensing Versioning Life-cycle management Visual assembly Event notification Configuration & property management Scripting Metadata & introspection Transaction control, locking Persistence Self-testing Self-installation Ease-of use Relationships: e.g. containment Supercomponent [Orfali, Harkey] MIT IAP 1999

  6. Component Software Goals • Reuse components raise the bar of what can be reused • Distributed components compatibility transparent distributed computing MIT IAP 1999

  7. Developers Development time & effort Cost Reliability Flexibility End users Custom software specialized, smaller, extensible Integration compound documents, drag & drop Scripting Ease of use Cost Component Software advantages MIT IAP 1999

  8. Buy or Write? flexibility nimbleness competitive edge cost efficiency 0 % bought 100 MIT IAP 1999

  9. Reuse approaches • Libraries • layered, object-oriented • deficiencies: • too fine grained • no location transparency • language specific: low-level workarounds • extension: source needed, fragile base classes • versioning • persistence MIT IAP 1999

  10. Reuse approaches 2 • Frameworks • Set of cooperating classes, that make up a reusable design for specific class of software • Extended: inheritance [template methods] • “Don’t call us, we’ll call you” • Deficiencies: • cannot be composed • language specific • Others: design patterns, languages MIT IAP 1999

  11. Component examples • Visual Basic • Modern operating systems • Plug-ins • Netscape, Photoshop, Quicktime, Mac OS • Emacs packages • Compound documents MIT IAP 1999

  12. Some component types • middleware components • logic components • vertical components • GUI components • container components MIT IAP 1999

  13. Component standards • COM - Microsoft [1993] • DCOM, COM+, OLE, ActiveX • CORBA - 700+ companies. • implementations “ORBs”: Iona Orbix, IBM SOM • OpenDoc • JavaBeans - Sun MIT IAP 1999

  14. Component basics • Interfaces, interface description languages, type libraries • Interoperability • Dynamic invocation (late binding) • Naming • Versioning • Persistence • Lifecycle management MIT IAP 1999

  15. Interfaces • Contract between client and implementation • abstraction • COM/CORBA objects != C++ objects • Example: IUnknown QueryInterface(CLSID, IID) AddRef() Release() • Interface inheritance • Multiple interfaces per component interface interface COM object interface MIT IAP 1999

  16. Interface descriptions • Interface description languages • COM IDL, CORBA IDL • type libraries • Reflection • preserve compile-time information for run-time inspection • Java, COM+ • Dynamic invocation MIT IAP 1999

  17. Interoperability • COM: binary standard • C++ vtable • CORBA: standardized language bindings • Location transparency: stubs & proxies • same code for: in-process, out-of-process, remote • marshalling RPC MIT IAP 1999

  18. Dynamic invocation • Late binding: scripting • Need dynamically built stubs, proxies, type checking • COM: dispatch interfaces • an interface with only one method: Invoke • method selected with dispatch id (DISPID) MIT IAP 1999

  19. Naming • How name components, interfaces, objects? • GUID or UUID - globally unique identifier • COM: 128 bit number • Java: hierarchical naming scheme • Directory: registry, interface repository MIT IAP 1999

  20. Versioning • Major, Minor version numbers: 5.1.32 • passing object references? • COM: • immutable interfaces • IIDs can be generic • CoTreatAsClass - IID redirection MIT IAP 1999

  21. Persistence • Example: save a compound document • Filesystem within a file • “Structured storages” (COM) • Related: serialization, externalization MIT IAP 1999

  22. Lifecycle management • Reference counting • COM: IUnknown Addref, Release • Automatic garbage collection (JavaBeans) • Remote liveliness: • PING protocol MIT IAP 1999

More Related