The goal of this section is to give you enough information so that you can read and use the Product Advertising API WSDL. You typically read a WSDL to understand value types, operation definitions, and request and response formats.

A WSDL (Web Service Description Language) is an XML document that defines the operations, parameters, requests, and responses used in web service interactions. You can think of a WSDL as the contract that defines the language and grammar used by web service clients and servers. When you look at the Product Advertising API WSDL, for example, you find in it all of the Product Advertising API operation names, parameters, request and response structures.

There is not a single WSDL. Product Advertising API, for example, has many different versions of its WSDL—the latest one and all of its previous versions. Not only can one company use different versions of a WSDL, every company can use its own WSDL based on its own APIs or business metrics. For that reason, web service requests must identify the WSDL they use so the web servers know how to interpret the requests.

In practice, Product Advertising API developers use the same version of the Product Advertising API WSDL in every request in a session. Over time, they might send requests to the latest Product Advertising API WSDL. The Product Advertising API WSDL is upgraded regularly.