On 12th August 2003 WS-I (Web Services Interoperability Organization) announced the release of the final specification of Basic Profile 1.0 a set of recommendations on how to use web services specifications to maximize interoperability. For developers, users, and vendors of web services and web services tools this is a big leap forward to achieving interoperability in the emerging and fast changing world of web services. But what else has WS-I been working on?

In my prior articles, I've introduced and discussed various aspects of the JAX Pack, a set of APIs for working with Web services and the underlying supporting protocols. In this article, we'll look at JAX-RPC, a specification for making remote procedure calls via XML and SOAP over HTTP. Specifically we'll look at the client side of JAX-RPC, as it shows the most promise.

Overloaded methods may or may not be what you need for the project you are working on. Additionally, there are those who argue that if a function is taking a different set of argument-types, then it should be noted by giving it a different name. But neither of these are the argument for learning how to express overloaded interfaces in WSDL. The reason is simple: languages, commercially in use today, support this feature. In order to correctly describe their interfaces using a description written in WSDL, it must be possible to describe an operation that has different calling syntaxes.

In a previous article ("WSDL Tales From the Trenches, Part 1"), I painted a big picture of web services design. As I said, Web Services Description Language (WSDL) only defines the syntax of how a web service may be invoked; it says nothing about its semantics. I will observe this distinction in what I say in this article about WSDL.

One of the best aspects of WSDL is that you rarely have to create WSDL files from scratch. A whole host of tools currently exists for transforming existing services into WSDL descriptions.

Our initial discussion of WSDL invocation tools focused on programming and command-line invocation tools. We now move on to even simpler tools that are entirely driven by a web-based interface.

In a previous article I explained how to use Soap Extensions to extend and customize the process of sending and receiving Soap messages. But for all this to work, the server needs to tell the client which extensions it is using. The place to declare this information is the WSDL document, the document that acts as a contract between de client and the server.

Now that we recognize the limitations of existing Web services toolkits, it is time for us to examine the real problem. The foremost question that pops up is this: Is WSDL itself flawed? The answer, in all fairness, is "not really."

WSDL is a specification defining how to describe web services in a common XML grammar. WSDL describes four critical pieces of data:

In order for a person or company to run a Web service, basic information about that Web service needs to be provided - information such as where the service is located, how the service can be bound to, and similar information. All this information is provided by a Web Services Description Language (WSDL) document. In this column, we'll take a look at what WSDL is, how it works, and what the future may hold for WSDL.

Let's start with understanding what web services mean. You must have heard this word zillion time now in the course of last two-three years.

This chapter will guide you through the creation of a simple "Hello World" Web service and client. This simple Web service echoes some text back to the client.

To explore complex types, consider the WSDL file in Example 6-10. This WSDL file describes our Product Service from Chapter 5. The complex types are indicated in bold.

In this hour, you will learn how WSDL is used to describe XML Web services. You will see how WSDL is used to define how a service exposes itself to various types of HTTP request types.

Web Services Description Language (WSDL) describes the technical details of how a Web Service works, detailing the technical requirements for uses such as its Internet address and port, method names and associated arguments, data types, and so on.

Recently I retrofitted WSDL to a set of existing web services. A customer had a server running and there was a client implementation. The client and server team had been working closely together and now the time had come for another client implementation by a development team on the other side of the globe. A clear specification of the services was needed, and that's what WSDL is for.

Web services vendors will tell you a story if you let them. "Web services are a cinch," they'll say. "Just write the same code you always do, and then press this button; presto, it's now a web service, deployed to the application server, with SOAP serializers, and a WSDL descriptor all written out."

One of the best aspects of WSDL is that you rarely have to create WSDL files from scratch. A whole host of tools currently exists for transforming existing services into WSDL descriptions. You can then choose to use these WSDL files as is or manually tweak them with your favorite text editor. In the discussion that follows, we explore the WSDL generation tool provided by GLUE.

First steps for Web service description processing

WSDL is used to describe SOAP over HTTP, HTTP-POST, HTTP-GET, SMTP, and others. With WSDL, SOAP is much easier to deal with both for developers and users. WSDL has a number of XML elements in its namespace. The following table summarizes those elements, their attributes, and children.