A Web service is an application that can be consumed (accessed and used) over the Internet (or an intranet) using industry-standard protocols. To consume this application, a client (Web service client) invokes operations that are described using Web Services Description Language (WSDL) and sent to the application using Simple Object Access Protocol (SOAP) over HTTP (or HTTPS). The application executes the operations and returns the results to the client using SOAP over HTTP/S. A Web service provider (Web application server) hosts the Web service and manages all communications between it and its clients. Simply put, Web services provide an industry-standard way for all types of client applications to call functions on all types of application servers, over any network configuration that supports SOAP over HTTP, and where the application program interface (API) can be described using WSDL.
Note: Web services standards mention other possible communications and transport protocols besides SOAP over HTTP. However, OpenEdge supports the most common Web service standard, which is SOAP over HTTP.
The key words in defining Web services are industry standards. Web services represent a widely accepted set of industry standards that allow distributed applications to communicate and exchange data without concern for each other’s specific platform requirements.
These standards combine and extend technologies that are universally accepted for one purpose (HTTP for the World Wide Web) or are now widely used to develop standard applications for many purposes (XML). They have arisen from a collaboration of industry representatives who have formed standards bodies to develop and support them. Two of the most important such bodies include the Web Services Interoperability Organization (WS-I), which promotes the development of standardized interactions between Web services and tools to validate them, and the World Wide Web Consortium (W3C), which coordinates and publishes the specifications for most of the standards that support Web services development, such as HTTP and the XML-based standards, SOAP and WSDL.
The following sections describe the basic components of Web services and the standard architecture that supports them.
