Orbeon's OXF is used to manage the screen pipelines providing a rich pipeline language that can invoke arbitrary processors
Processing logic exists in four types of XML files:
Controller Files
Orchestrate transitions between pages and send screen input to be processed
Model Files
Define the page construction and application logic
View Files
Lay out the page controls and the elements to receive styling
Action Files
User input processing and the resulting application logic
OXF allows us wrap existing business logic as processor which can be invoked within an application's workflow
Example: we wrote a processor that does business rule validation using Schematron