I'm not an expert on Web Services. This is just an attempt to provide a basic, simple introduction for CompShack visitors. Please feel free to comment or suggest any additions to the topic.
What is a Web Service?
From how I understand it, a Web Service is a set of technologies based on a set of standards to build applications that can "talk" to each other. In other words, Web Service is an application that exists over the web.
Web services are self describing by using WSDL documents (more on this later). The document describes web service data type information, and message structure. It also describes what the service does and how it could be accessed.
Why do we need Web Services?
Some of the major challenges that different systems faces while trying to communicate with each other are operating system dependency, programming languages dependency, and custom file format that each system has.
Web Services address all these issues by providing parties with major benefits such as no operating system dependency, no programming dependency since all messages are being transmitted in a standard XML. Another benefit of using web services is that they are easily accessible via standard protocols like http and https.
What does a Web Service Consists of?
Universal Description, Discovery, & Integration (UDDI): Simply put, this is a central place where you can search if a particular service is available to perform certain functionality.
Web Services Description Language (WSDL): Is a document that describes a specific web service. The description includes the message structure or format, the messaging protocols, and some network information. All information needed to invoke the web service should be included in the WSDL document.
To invoke a web service over a network you would need to use SOAP (Simple Object Access Protocol). SOAP is an XML based messaging protocol that defines a set of rules for structuring messages that can be used for Remote Procedure Call (RPC) request-response dialogues. HTTP is a popular transport protocol for SOAP.
Little Bit About a Web Service Process
Three different stages for a web service process – discovery, development and the run time.
Discovery - Identify wither a particular service is available. This could be accomplished in two ways. The 3rd party hits a URL that you have provided for them to get the WSDL file or you can simply provide a copy of the generated WSDL file to them. Again the WSDL file will provide detailed information about that particular web service.
Development – Import the WSDL file to 3rd party application, some coding might be needed to tweak the file and add some more logic to it.
Runtime – Is simply when you send your messages to the web service. The messages are wrapped by SOAP and transported via the popularly used HTTP protocol.
Types of PeopleSoft Web Services
Two types of PeopleSoft web services: