RIKA: Component Architectures

Transcription

1 RIKA: Component Architectures Dr. Detlef Kreuz Telematik TUHH - TELEMATIK Agenda Introduction What you should learn from this talk N-Tier applications Designing with components What is a component? Why using components? The interface idea Example component architectures CORBA RMI DCOM TUHH - TELEMATIK 2

2 What you should learn from this talk Most important Think in interfaces! Knowledge of the component idea What is a component? Designing with components? How using components? Differences between components and interfaces Knowledge about different component architectures CORBA, RMI, DCOM Advantages and disadvantages Selection criteria for your own project TUHH - TELEMATIK 3 N-Tier: An Example Client Web Server Servlet JSP Application Components DB TUHH - TELEMATIK 4

3 A Software-Bus Component Component Software-Bus Component TUHH - TELEMATIK 5 What is a component? A component is a piece of software small enough to be created and maintained by few persons big enough to provide useful functionality to justify individual support provided with standardized interfaces to co-operate with other components Examples Naming components: maps names to components Database components: provides access to databases UI components: buttons, text boxes, list boxes,... TUHH - TELEMATIK 6

4 Why using components? Faster development design pattern reusability of existing components Better integration standardized interfaces Independence Operating system Programming language Higher flexibility replacement of components Lesser debugging, maintenance focussing on single component TUHH - TELEMATIK 7 Interfaces Components provides Services An Interface describes what service a component provides... describes not how this service is implemented (separation of what and how )... is the key for accessing components Language for the description of interfaces independent of programming languages (!?!) independent of implementations mapping needed restricted to syntactical aspects TUHH - TELEMATIK 8

5 Designing with Components Most important Design the right interfaces UI mapping UI UI mapping Create problem specific interfaces Business logic UI access Database access Why interfaces for UI and DB tier? Flexibility Adaptability Handiness Last important Interface implementation Common services DB access DB DB access Common services TUHH - TELEMATIK 9 Component Architectures: Overview CORBA - Common Object Request Broker Architecture open component architecture under control of industry consortium focuses on interoperability RMI - Remote Method Invocation component architecture for Java under control of Sun, ISO (?) partially interoperability with CORBA focuses on integration into the Java programming language DCOM - Distributed Component Object Model open, proprietary component architecture under control of Microsoft focuses on ease of use and integration into Windows platform TUHH - TELEMATIK 10

6 CORBA Standardized by OMG (Object Management Group) part of the Object Management Architecture (OMA) Object-based approach objects are implementing interfaces object are referenced Focussing on interface description Interface Definition Language (IDL) Standardized language mappings C, C++, Java, COBOL, Ada, Smalltalk Python, Tcl,... Broker model ORB acts as a mediator between client and object implementation ORB is only conceptual TUHH - TELEMATIK 11 Object Management Architecture Application Objects Common Facilities Object Request Broker (ORB) Common Object Services TUHH - TELEMATIK 12

7 Method invocation Client Object Implementation Request ORB TUHH - TELEMATIK 13 Structure of an Object Request Broker Client Object Implementation Dynamic Invocation IDL Stubs ORB Interface Static IDL Skeleton Dynamic Skeleton Ob ject Adapter ORB Core Interface identical for all ORB implementations There may be multiple object adapters There are stubs and a skeleton for each object type ORB-depe ndent interface Up-call interface Normal call interface TUHH - TELEMATIK 14

8 Common Object Services Standardized Basic Services Naming service Event service Time service Lifecycle service Relationship service Transaction service Property service Trading object service TUHH - TELEMATIK 15 Java Remote Method Invocation Main objective seamless access of remote and local objects independent of network transport mechanism Access through Java interfaces remote interface extends java.rmi.remote all operation can throw exception java.rmi.remoteexception Services Simple naming service Activation (and deactivation) of objects Types of objects remote objects: implementing java.rmi.remote transferable objects: implementing java.io.serializable non-transferable objects, e.g. DB access objects,... TUHH - TELEMATIK 16 More information at the Java RMI tutorial!

9 Distributed Component Object Model Main objective reusability of components focuses on components, no notation of objects seamless access of remote and local components Interfaces Similar to abstract C++ classes with virtual functions More than one interface per component Predefined methods QueryInterface: get other interfaces AddRef, Release: component lifecycle management Tools - makes the life easier Visual Basic, Visual J++: implementing components Microsoft Transaction Server: execution environment TUHH - TELEMATIK 17 Comparison CORBA + Interoperability + Common services + Openness Ease of use RMI + Integrated into Java Platform ± Ease of use ± Common services Other platforms DCOM + Tool support + Windows Platform + Ease of use ± Common services Openness Interoperability TUHH - TELEMATIK 18