Data-centric applications can have many different architectures. In some of these architectures, the data is not even in the database itself. In these cases, a possible scenario can be that the data is collected by calling webservices.

Essentially, a webservice provider offers a way for external applications to unlock its data, but not give away total access to its database (or other datasources).

A call to a webservice will have to satisfy certain standards as set by the World Wide Web consortium (W3C). Since the fourth version of Application Express, it provides the possibility to natively call two of these standards: Simple Object Access Protocol (SOAP) and Representational State Transfer (REST). But, by using a little more PL/SQL and XML DB, it's possible to use any type of webservice in APEX.

In this chapter, we are going to create some examples of how to use webservices in APEX.