Web service--The next generation www[turn]

The word Web service seems to be heating up overnight. A Web service is an online application service issued by an enterprise that completes its particular business needs, and other companies or applications can access and use the online services over the Internet.
The Web service is the next generation of WWW, which allows you to place programmable elements on a Web site that can perform distributed computing and processing based on the web. Web Service has developed very quickly, and the building blocks of this new specification (SOAP, WSDL, and UDDI) have had a dramatic impact on the design, development, and deployment of web-based applications for only a few months. The giants of the software industry and the Internet-era software nouveau riche have begun a new round of competition in this area.

Web Service
The characteristics
Web Service is a collection of features that are encapsulated into a single entity and published to the network for use by other programs. Web Service is a widget for creating open distributed systems that enables companies and individuals to deliver their data services to the world quickly and cheaply.
Web Service is the core of the next generation distributed system, it has the following characteristics:
Interoperability: Any Web service can interact with other Web service. With soap (simple Object Access Protocol) a new standard protocol supported by all major vendors, it avoids the hassle of switching between CORBA, DCOM, and other protocols. And because you can write Web service in any language, developers can produce and use Web service without having to change their development environment.
Universality: Web service uses HTTP and XML for communication. Therefore, any device that supports these technologies can have and access the Web Service.
Easy to use: The concepts behind Web service are easy to understand, and free toolkits from vendors such as IBM and Microsoft enable developers to quickly create and deploy Web service. In addition, some of these toolkits can make existing COM components and JavaBean easy to become Web Service.
Industry support: All major vendors support SOAP and peripheral Web service technologies. For example, Microsoft's. Net platform is based on Web service, so components written in Visual Basic are easy to deploy as Web service and can be used by Web service written by IBM VisualAge.
Web Service
The architecture
Web Service is an independent, modular application that can be described, published, positioned, and invoked through the web, especially www. The architecture of the Web service describes three roles (service providers, service requesters, service agents), and three operations (publish, find, bind).
Service providers configure and publish services by registering with the Service Broker, where the service requester finds the service by looking up the registration records of the published service that the service agent has, and the service requester binds the service provider and uses the available services.
In the world of Web service, three operations contain three highly praised but distinct technologies. Publishing services use UDDI (uniform description, Discovery, and integration) to find services that use a combination of UDDI and WSDL (WEB Service Description Language), and bind services use WSDL and SOAP. In three operations, the binding operation is the most important, and it contains the actual use of the service, which is also where interoperability issues occur. It is because the full support of the SOAP specification by service providers and service requesters solves these problems and enables seamless interoperability.
When developers develop new applications, they can find the required web Service on the UDDI registry via the UDDI operator or the UDDI Search engine Web interface, and then within the UDDI registry, or through UDDI The connection in registry finds the calling specification for the Web service, which is generally described using WSDL. The developer can use development tools or call the specification manually, and then add the Web service invocation defined by the calling specification in its own application. The application developed in this way can invoke the specified Web service through SOAP.
For services or applications with automated integration-related applications (application), user applications access UDDI operator or UDDI Registry via the SOAP protocol to find the web Service,uddi needed Operator and UDDI Registry will respond to the invocation specification of the Web service and the invocation specification via the SOAP protocol, the application gets the canonical text of the service invocation using the WSDL description, and automatically invokes the interface bindings by parsing the descriptive text, And bind the required call parameters appropriately and complete the call.
Simple objects
Access Protocol Soap
Soap is an xml-based presentation layer protocol that is not dependent on transport protocols, and is used to easily exchange data between applications in the form of objects. The lower layers of soap can be http/http, or SMTP/POP3, or special communication protocols specifically designed for some applications.
SOAP provides a simple, lightweight mechanism for exchanging structured and type information in a decentralized or distributed environment in the form of XML. SOAP itself does not define any application semantics, such as a programming model or an implementation of a particular semantics; in fact, it defines a simple mechanism for representing application semantics by providing a package model with standard components and a mechanism for encoding data in modules. This enables soap to be used for various systems that are passed from message to RPC.
SOAP consists of three parts:
SOAP Encapsulation Structure: Defines an overall framework that represents what is contained in a message, who handles it, and whether the content is optional or required.
SOAP Encoding Rules: Defines a series of mechanisms for exchanging instances of application-defined data types.
SOAP RPC representation: Defines a contract to represent remote procedure calls and replies.
In addition to the SOAP encapsulation, SOAP encoding rules, and SOAP RPC protocols, this specification defines the binding of two protocols, describing how a SOAP message is included in an HTTP message if there is or is no HTTP extension framework.
Unified Description,
Discovery and Integration Protocol UDDI
UDDI is a web-based, distributed, implementation-standard specification for Web service-provided information registries, as well as a set of implementation standards that enable enterprises to register their own web service to enable other enterprises to discover.
The core component of UDDI is UDDI business registration, which uses an XML document to describe the enterprise and the Web service it provides. Conceptually, the information provided by UDDI Business registration consists of three parts:
White page: Includes address, contact method, and known enterprise identity.
Yellow Pages (Yellow page): Includes industry categories based on the standard taxonomy.
Green page: Includes technical information about the Web service provided by the enterprise, in the form of pointers to files or URLs that are serviced by the service discovery mechanism.
All UDDI Business registration information is stored in the UDDI Business Registration center. By using the discovery services of UDDI, organizations can register their own web service offerings that they want to be found by other businesses. Companies can add information to the business Registry of UDDI through the UDDI Business Registry Web interface, or by using tools that implement the programming interfaces described in the UDDI Programmer ' API standard. The UDDI Business Registry is logically centralized, physically distributed, and consists of multiple root nodes, which synchronize data with each other in a certain set of rules. When an enterprise is registered in an instance of the UDDI Business Registry, its registration information is automatically replicated to other UDDI root nodes, so that it can be found by anyone who wishes to discover these Web service.
Web Services
Description Language WSDL
With the standardization of communication protocols and message formats in the Web, it becomes more and more important to describe communication in some format, and the likelihood of its implementation is increasing. This requirement is met by a network service approach that is described in a set of XML syntax defined by WSDL. WSDL defines a network service as a set of communication endpoints that can exchange messages. The WSDL service provides a help document for distributed systems, and also serves as a solution for automating communication between applications.
A WSDL document defines a service as a collection of network endpoints, or a collection of ports. In WSDL, the abstract definition of endpoints and messages is separate from their specific network implementations and data format bindings. This allows you to reuse these abstract definitions: messages, abstract descriptions of the data that needs to be exchanged, port types, and abstract collections of operations. A reusable binding is formed for specific protocols and data format specifications for a particular port type. A port is defined as a network address and a reusable bound join, and the set of ports is defined as a service. Therefore, a WSDL document uses the following elements when defining a network service:
Type: Defines a data type using some type of system, such as XSD.
Message: A typed definition of the communication data abstraction.
Action: An abstract description of the actions supported by the service.
Port type: An abstract collection of operations that is supported by one or more endpoints.
Binding: A specific protocol specification and data format specification for a specific port type.
PORT: A single endpoint defined as a binding and a join of a network address.
Service: A collection of related endpoints.