Document-Based Web Services

In the RPC-based interaction, the web service is viewed by the consumer as a single logical application or component with encapsulated data, where the WSDL described by the
publicly-exposed interface and the XML in the SOAP messages exchanged is formatted to map to the discrete operations exposed by that application. In fact, the messages directly
map onto input and output parameters of the procedure calls or operations. Typically, such invocations occur over a synchronous transport protocol like HTTP, where the SOAP
request and response is piggybacked on the protocol-level request-and-response, respectively, to form synchronous request-response interaction patterns. For example, see Figure
1, which illustrates a payment service that accepts payments and returns a status, or a stock quote service that accepts a ticker symbol and returns the current quote in the HTTP
response.

In a document-based interaction, the service consumer interacts with the service using documents that are meant to be processed as complete entities. These documents typically
take the form of XML, which is defined by a commonly agreed upon schema between the service provider and service consumer. It is also possible that the document exchanged in
such an interaction could be in a format other than XML (such as encrypted files); however, the value of agreeing on a XML schema is to facilitate interoperability. In other words,
the document represents a complete unit of information and may be completely self-describing.

Document-based message exchanges are more common to asynchronous communication architectures. Also, the effort and complexity involved in building a document-oriented web service is usually more than the effort involved in using an RPC-based architecture. This is because it involves extra steps, such as designing the schema for the documents that will be
exchanged, negotiating and arriving at an agreement with business partners on that design, and validating the document against the schema.

A SOAP message on the wire can be represented in either RPC style or document style. This choice is governed by the value of the style attribute in the WSDL file.

Development of a document-driven web service typically starts with the definition of the schemas and the WSDL describing the document exchange.