Parsing Web Interface Description Language WSDL (1)

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The Web Service Definition language (Web Services definitions LANGUAGE,WSDL) is a recommended standard for describing the technical invocation syntax of a Web service. WSDL defines a set of xml-based syntax that satisfies this requirement by describing the Web service as a collection of service access points that can be exchanged for messages. The WSDL service definition provides a machine-aware SDK documentation for distributed systems and can be used to describe the details involved in automating application communication. The current version of WSDL is 1.1, and the specification can be obtained from HTTP://WWW.W3.ORG/TR/WSDL.

WSDL is the standard XML format for describing Xmlweb services, which are presented by Ariba, Intel, IBM, and Microsoft. It defines the actions and messages sent and received by a given Web service in an abstract way that is not specific to language. As a definition, you cannot use WSDL as an Object interface definition language, for example, application architectures such as CORBA or COM are used for object interface definition languages. WSDL remains protocol neutral, but it does have built-in support for binding soap, thus creating an inextricable link with soap.

A WSDL service description is an XML document that is consistent with the definition of a WSDL schema (schema). The WSDL document is not a complete service description, but only a lower level of the service description task: The original technical description of the service interface. WSDL is the interface Definition language IDL (Interface definition Language) of a Web service, and in essence the WSDL description describes the following three basic properties of the Web service:

What the service does-the actions (methods) that the service provides.
How to access Services-data format details and the necessary protocols for accessing service operations.
Where the service is located-a network address, such as a URL, that is determined by a specific protocol.

Second, WSDL document structure

A WSDL document defines a Web service as a collection of service access points or ports. In WSDL, because the abstract definition of a service access point and message has been separated from a specific service deployment or data format binding, the abstract definition can be reused: a message, an abstract description of the exchanged data; the port type refers to an abstract collection of operations. The specific protocol and data format specification for a particular port type constitutes a binding that can be used again. The Web Access address is associated with a reusable binding, you can define a port, and the collection of ports is defined as a service.

1. WSDL Information Model

The WSDL Information model fully utilizes the separation between the abstract specification and the specification implementation, which separates the service interface definition (abstract interface) and the service implementation definition (concrete endpoint). The abstract interface specification describes the processing power of the terminal, which is represented as porttype in the WSDL. The Banding mechanism (binding mechanism) is represented in WSDL as the binding element, which maps the abstract definition of a Web service to a specific implementation using a specific communication protocol, data encoding model, and underlying communication protocol. If the bundle is bound to the access address of the implementation, the abstract endpoint becomes the specific endpoint (concrete endpoint) that the service requester invokes, and the port element of the WSDL represents this combination.

An abstract interface can support any number of operations (operations). The action is defined by a set of messages (messages) that define the interaction of the operation. The concrete implementation that corresponds to the abstract message and operation concept is specified by the binding element. As with XML applications, the WSDL schema defines several high-level elements, or the primary elements. In WSDL, the main elements in the Web Service description are as follows:

Types defines the collection of all data types used by the Web service, which can be referenced by each message part of the element. It uses some kind of system (generally using the type system in XmlSchema).
Message, an abstract typed definition of a communication information structure. Use the type defined by types to define the data structure of the entire message.
Operation, an abstract description of the operations supported in the service. A general single operation describes a request/response message pair for an access portal.
PortType, an abstract collection of actions supported for an access entry point type. These actions can be supported by one or more service access points.
Binding, which includes how to transform the elements of an abstract interface (PortType) into specific representations of details, refers to the combination of specific data formats and protocols, the specific protocol for a particular port type, and the binding of the data format specification.
Port defines a single service access point that is a combination of protocol/data format bindings and a specific Web access address.
Service, which is a rough named element that represents a collection of ports, and a collection of related service access points.

Thus, PortType (combined with the details of the message and type elements) describes what a Web service is, and the binding element describes how the Web service is used, and the port and service elements describe the location of the Web service.

Figure 1 WSDL Information model

Figure 1 illustrates a possible structure of the WSDL information model, which clearly reflects the relationship between the abstract message/operation and the specific message/operation of the binding element contained in the porttype element. The bold characters in the figure highlight the terminology in the WSDL specification. The element names used by WSDL are somewhat ambiguous, and since there is no consistent naming principle that distinguishes between abstraction and specific concepts, it is important to remember which element represents an abstract concept and which one represents a specific concept.