While discussing composer functionality for extending Fusion Applications I encountered many questions about the four Composers provided by Oracle
- The Application User Interface, supported by the Page Composer
- The Application Data Model, supported by the Data Composer
- Business Process Management, supported by the Process Composer
- Business Analytics, supported by the BI Composer
There is a very goog blog The Four Fusion Application Composers Explained written by Richard Bingham. That explains different composers and their use cases.