WSDL 2.0 Introduction

WSDL 2.0 Introduction

Web Services Description Language Version 2.0 (WSDL 2.0) provides a model and an XML format for describing Web services. WSDL 2.0 enables one to separate the description of the abstract functionality offered by a service from concrete details of a service description such as “how” and “where” that functionality is offered.

This specification defines a language for describing the abstract functionality of a service as well as a framework for describing the concrete details of a service description. It also defines the conformance criteria for documents in this language.

The companion specification, Web Services Description Language (WSDL) Version 2.0 Part 2: Adjuncts [WSDL 2.0 Adjuncts] describes extensions for message exchange patterns, operation safety, operation styles and binding extensions (for SOAP [SOAP 1.2 Part 1: Messaging Framework (Second Edition)] and HTTP [IETF RFC 2616]).

WSDL - Service Description

WSDL 2.0 describes a Web service in two fundamental stages: one abstract and one concrete. Within each stage, the description uses a number of constructs to promote reusability of the description and to separate independent design concerns.

At an abstract level, WSDL 2.0 describes a Web service in terms of the messages it sends and receives; messages are described independent of a specific wire format using a type system, typically XML Schema.

An operation associates a message exchange pattern with one or more messages. A message exchange pattern identifies the sequence and cardinality of messages sent and/or received as well as who they are logically sent to and/or received from. An interface groups together operations without any commitment to transport or wire format.

At a concrete level, a binding specifies transport and wire format details for one or more interfaces. An endpoint associates a network address with a binding. And finally, a service groups together endpoints that implement a common interface.

The Meaning of a Service Description

A WSDL 2.0 service description indicates how potential clients are intended to interact with the described service. It represents an assertion that the described service fully implements and conforms to what the WSDL 2.0 document describes. For example, as further explained in section 6.1.1 Mandatory extensions, if the WSDL 2.0 document specifies a particular optional extension, the functionality implied by that extension is only optional to the client. It must be supported by the Web service.

A WSDL 2.0 interface describes potential interactions with a Web service, not required interactions. The declaration of an operation in a WSDL 2.0 interface is not an assertion that the interaction described by the operation must occur. Rather it is an assertion that if such an interaction is (somehow) initiated, then the declared operation describes how that interaction is intended to occur.