WSDL language basics

The Web Services Description Language (WSDL) is the most fundamental technology standard associated with the design of services. As you will see in subsequent chapters, WSDL definitions are a central part of all aspects of service design. In Chapter 5 we introduced the WSDL document and established how it consists of separate abstract and concrete definitions.

Just to recap, the abstract definition contains a series of parts that include types, message, and port type (or interface), whereas the concrete definition is comprised of binding and service parts.

Each of these parts relates to corresponding elements (Figure 13.4) that are defined in the WSDL specification. In the following sections we describe the syntactical implementation of these elements, as they are relevant to the majority of upcoming case study examples used in Chapter 15 to demonstrate service interface design. (How WSDL relates to SOA is discussed separately in the WSDL and SOA section of Chapter 14.)

Figure 13.4. The structure of a WSDL definition.

13.3.1. The definitions element

This is the root or parent element of every WSDL document. It houses all other parts of the service definition and is also the location in which the many namespaces used within WSDL documents are established.

Example 13.6. A definitions element of the Employee Service, declaring a number of namespaces.

<definitions name="Employee" targetNamespace="http://www.xmltc.com/tls/employee/wsdl/" xmlns="http://schemas.xmlsoap.org/wsdl/" xmlns:act="http://www.xmltc.com/tls/employee/schema/accounting/" xmlns:hr="http://www.xmltc.com/tls/employee/schema/hr/" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="http://www.xmltc.com/tls/employee/wsdl/" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> ...