9. Socket programming Sockets provide a low-level API for writing distributed client/server applications. Before a client communicates with a server, a socket endpoint needs to be created. The transport protocol chosen for communications can be either TCP or UDP in the TCP/IP protocol stack. The client also needs to specify the hostname and port number that the server process is listening on.
11. RPC is another mechanism that can be used to construct distributed client/server applications. RPC can use either TCP or UDP for its transport protocol. RPC relies heavily on an Interface Definition Language (IDL) interface to describe the remote procedures executing on the server-side. From an RPC IDL interface, an RPC compiler can automatically generate a client-side stub and a server-side skeleton. With the help of the stub and skeleton, RPC hides the low-level communication and provides a high level communication abstraction for a client to directly call a remote procedure as if the procedure were local. RPC
13. Java RMI The Java RMI is an object-oriented mechanism from Sun Microsystems for building distributed client/server applications. Java RMI is an RPC implementation in Java. Similar to RPC, Java RMI hides the low-level communications between client and server by using a client-side stub and a server-side skeleton (which is not needed in Java 1.2 or later) that are automatically generated from a class that extends java.rmi.UnicastRemoteObject and implements an RMI Remote interface.
15. DCOM The Component Object Model (COM) is a binary standard for building Microsoft-based component applications, which is independent of the implementation language. DCOM is an extension to COM for distributed client/server applications. Similar to RPC, DCOM hides the low-level communication by automatically generating a client-side stub (called proxy in DCOM) and a server-side skeleton (called stub in DCOM) using Microsoft’s Interface Definition Language (MIDL) interface. DCOM uses a protocol called the Object Remote Procedure Call (ORPC) to invoke remote COM components.
18. CORBA CORBA is an object-oriented middleware infrastructure from Object Management Group (OMG) for building distributed client/server applications. Similar to Java RMI and DCOM, CORBA hides the low-level communication between the client and server by automatically generating a client-side stub and a server-side skeleton through an Interface Definition Language (IDL) interface. CORBA uses Internet-Inter ORB Protocol (IIOP) to invoke remote CORBA objects. The Object Request Broker (ORB) is the core of CORBA; it performs data marshaling and un marshalling between CORBA clients and objects. Compared with Java RMI and DCOM, CORBA is independent of location, a particular platform or programming language. CORBA supports both synchronous and asynchronous communications.
26. A summary on Java RMI, DCOM and CORBA Java RMI, DCOM and CORBA have all been around for some time and represent the most popular distributed, object-oriented middleware which can be used to rapidly develop distributed client/ server applications. They use proprietary communication protocols – e.g. Java RMI uses JRMP, DCOM uses ORPC and CORBA uses IIOP – to invoke remote objects or components. middleware such as Java RMI, DCOM and CORBA are not based on open standards, which makes it dif.cult for them to be ubiquitously taken up in heterogeneous environments. Ideally, what is needed is an open standards-based middleware infrastructure for building and integrating applications in heterogeneous environments, and Web services are emerging as such an infrastructure.
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34. Anatomy of a Service Service Consumer Interface Proxy Service Interface Service Implementation New Service Wrapped Legacy Composite Service
39. WEB SERVICES Web services are emerging as a promising infrastructure for building distributed applications. Web services are based on a Service-Oriented Architecture (SOA) in which clients are service requestors and servers are service providers. Web services differ from other approaches such as Java RMI, CORBA and DCOM in their focus on simple open standards such as XML and HTTP, which have wide industry support and a chance of becoming truly ubiquitous. Essentially, a Web service is a loosely coupled, encapsulated, platform and programming language neutral, composable server-side component that can be described, published, discovered and invoked over an internal network or on the Internet.
40. • Loosely coupled : A Web service implementation is free to change without unduly impacting the service client as long as the service interface remains the same. • Encapsulated : The implementation of a Web service is completely invisible to the client of a service. • Platform and programming language neutral : A Web service can be implemented in any language and deployed on any platform. • Composable : A Web service can be composed from a number of deployed services. • Server-side component : A Web service can range in scope from a complete application to a subroutine that runs on a server.
41. • Described : An XML-based interface is used to describe the functionality and capabilities that a Web service can provide. • Published : A Web service can be registered with a service registry that can be accessed on an intranet or on the Internet. • Discovered : A Web service client can discover a service by searching a service registry and match their service requirements. • Invoked : A Web service can be bound to by a service client via standard transport protocols such as HTTP or FTP. • Internal network or the Internet : A Web service can be made available strictly within an organization or it can be offered across the.rewall, available to any consumer connected to the Internet.
42. What are Web Services? Web services are application components Web services communicate using open protocols Web services are self-contained and self-describing Web services can be discovered using UDDI Web services can be used by other applications XML is the basis for Web services
43. How Does it Work? The basic Web services platform is XML + HTTP. The HTTP protocol is the most used Internet protocol. XML provides a language which can be used between different platforms and programming languages and still express complex messages and functions. Web services platform elements SOAP (Simple Object Access Protocol) UDDI (Universal Description, Discovery and Integration) WSDL (Web Services Description Language)
44. Web services have two types of uses. Reusable application components There are things different applications needs very often. So why make these over and over again? Web services can offer application components like currency conversion, weather reports or even language translation as services. Ideally, there will only be one type of each application component, and anyone can use it in their application. Connect existing software Web services help solve the interoperability problem by giving different applications a way to link their data. Using Web services you can exchange data between different applications and different platforms.
45. Web Services have three basic platform elements. These are called SOAP, WSDL and UDDI.
46. What is SOAP? The basic Web services platform is XML plus HTTP. SOAP stands for Simple Object Access Protocol SOAP is a communication protocol SOAP is for communication between applications SOAP is a format for sending messages SOAP is designed to communicate via Internet SOAP is platform, language independent SOAP is based on XML SOAP is simple and extensible SOAP allows you to get around firewalls SOAP will be developed as a W3C standard
47. What is WSDL? WSDL is an XML-based language for describing Web services and how to access them. WSDL stands for Web Services Description Language WSDL is written in XML WSDL is an XML document WSDL is used to describe Web services WSDL is also used to locate Web services WSDL is not yet a W3C standard
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