Web Service Overview

If for nothing else, this post is for me (and others who are IT inclined) to serve as just a quick overview of web services, their high-level components, and some quick links:

Web Services
Web services are application components that communicate using XML and are transported using SOAP via the HTTP (an Internet) protocol. Web services are self-contained and self-described using WSDL. They can be discovered using UDDI. Web services are meant to be used by other applications. The combination of one or more web services can create an entire application containing application and system integration and cross-communication.

Simple Object Access Protocol (SOAP)
SOAP is an XML based protocol used for communication over the HTTP (an Internet) protocol. SOAP is a format for sending messagings in platform and language independant manner. SOAP contains the following structure:
- Envelope (required)
- Header (optional)
- Body (required)
- Fault (optional)

Web Services Description Language (WSDL)
WSDL is an XML based language specifying the location and methods of web services. A WSDL file may contain the location and methods for one or more web services. WSDL contains the following structure:
- portType (methods)
- message (messages used in methods)
- types (data types used by the web service)
- binding (communication protocols used by the web service - e.g., SOAP)

WSDL inherently describes the operation type: one-way (receive), request-response, solicit-response, notification (one-way send).

Universal Description, Discovery, and Integration (UDDI)
UDDI is a platform-independent framework for describing services, discovering businesses, and integrating business services by using the Internet.

Introduced in 2000, UDDI was once thought of as a directory to share available web services, both publicly and privately, to potential consumers. However, as web service standards and UDDI uses were refined, it appears as though UDDI is now more of an internal metadata directory for web service producers and consumers. In my limited research, it's not easy for someone to simply scour the Internet for available web services. While sites such as seekda! exist, large web service proponents such as Microsoft, IBM, and SAP have dismantled their public registry of web services. The best way to find a web service is to establish an old-fashioned relationship with a contact, and then inquire as to their specific web service offerings.