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Component Architecture (CORBA – RMI) -Shalini Pradhan Common Architectures Data Flow Systems Call and Return Systems Communicating Processes & Event Systems Data – Centered Systems (Repositories) Main Programs & Subroutines Object Oriented Systems Independent Components Batch Sequential & Control Loops Pipes and Filters Databases & Blackboards Virtual Machines Rule based systems Object Oriented Architecture Component Architecture Component Independent unit of Software It satisfies a set of behavior rules Component Architecture Specifices set of interfaces and rules of interaction [http://www-unix.mcs.anl.gov/~curfman/cca/web/cca_paper.html] How do Components Interact? Components interact via clearly specified interfaces iGetMoney() iReceiveItem() Interface Customer Supplier iReceiveInventory() iOrderInventory() iReceiveOrder() Wholesaler Retailer Focus on individual interfaces - precise external behavior (provided + required) - all implementation aspects completely hidden Component Architecture Standards CORBA Java Beans JavaBeans and Enterprise JavaBeans (EJB) are component architectures developed by Sun and its partners. COM CORBA is a distributed object specification supported by the OMG (Object Management Group), a consortium of over eight hundred partners. is Microsoft's component standard that forms the basis for interoperability among all Window-based applications. Java RMI (Remote Method Invocation) The Java remote method invocation system described in this specification has been specifically designed to operate in the Java environment. CORBA http://students.cec.wustl.edu/~dm9/DCA/CORBA.htm Advantages CORBA supports many existing languages. CORBA also supports mixing these languages within a single distributed application. CORBA supports both distribution and Object Orientation. CORBA is an industry standard. CORBA provides a high degree of interoperability. This insures that distributed objects built on top of different CORBA products can communicate. Over 600 companies back CORBA, including hardware companies, software companies, and cable companies, phone companies, banks, etc. Limitations Not free Harder to use costs can be substantial developer licenses ($800+ per developer) runtime licenses (cost varies with vendor) standardized extensions (“Object services” inOMG speak) add more costs no support for detecting software version mismatches runtime, sometimes resulting in silent errors Add-on to the language [http://www.ociweb.com/javasig/knowledgebase/February1998/RMI_CORBA.pdf] Application Manage constant diversity - Heterogeneous environment Good for accessing legacy systems especially if Java is not supported on the legacy platform Good for extending existing CORBA-based systems with Java Good for leveraging expertise in other languages as long as there is a CORBA binding for that language Java RMI Java language's RMI system assumes the homogeneous environment of the Java Virtual Machine, and the system can therefore take advantage of the Java object model whenever possible. Remote method invocation (RMI) is the action of invoking a method of a remote interface on a remote object. Most importantly, a method invocation on a remote object has the same syntax as a method invocation on a local object. [http://java.sun.com/products/jdk/1.1/docs/guide/rmi/spec/rmi-objmodel.doc.html#213] Java RMI The interfaces and classes that are responsible for specifying the remote behavior of the RMI system are defined in the java.rmi and the java.rmi.server java.rmi.registry packages. RMI Registry Client VM stub Server VM skeleton OBJ Advantages Simple to use - sending objects Integrated into platform implement “Serializable” interface optionally specify codebase automatic version mismatch detection remote method calls are nearly identical to normal method calls distributed garbage collection preserves automatic memory management Can pass objects Supports Distributed Processing Limitations Works in only Java Environment Not a full featured Middleware No mechanism for object description Server agents