Web services enable application-to-application interaction over the Web, regardless of platform, language, or data formats. The key ingredients, including Extensible Markup Language (XML), Simple Object Access Protocol (SOAP), Web Services Description Language (WSDL), REpresentational State Transfer (REST), Web Application Description Language (WADL), and Universal Description, Discovery, and Integration (UDDI), have been adopted across the entire software industry. Web services usually refer to services implemented and deployed in middle-tier application servers. However, in heterogeneous and disconnected environments, there is an increasing need to access stored procedures, as well as data and metadata, through Web services interfaces.

Oracle Database can access Web services through PL/SQL packages and Java classes deployed within the database. Consuming external Web services from the database, together with integration with the SQL engine, enables Enterprise Information Integration.