Programming Visual Basic 2005

How Web Services Work

Microsoft has used web services to mimic RPC (remote procedure calls). You ask for an "object" from a web service, and what you get back provides the public interface to an object running on the web service's server. You can interact with that object, calling methods and examining or setting properties. In this model, web services allow an object on the server to expose program logic to clients over the Internet. Clients call exposed methods on the web service using standard Internet protocols.

Typically, both ends of the connection communicate using SOAP messages (see the sidebar "SOAP"), which consist of self-describing, text-based XML documents.^[*]

SOAP

SOAP (Simple Object Access Protocol) is an XML grammar that's tailored for exchanging web service data. SOAP uses XML syntax to format its content. It is, by design, as simple as possible, and, it is very flexible. Since SOAP messages consist of XML, which is plain text, they can easily pass through firewalls, unlike many proprietary, binary formats.

SOAP is not limited to name/value pairs as HTTP-GET and HTTP-POST are. Instead, SOAP can also be used to send more complex objects, including datasets, classes, and other objects.

^[*] It is also possible to communicate via HTTP-GET or HTTP-POST requests.