A Catalog is a collection of named Command s (or Chain s) that can be used retrieve the set of commands that should be performed based on a symbolic identifier.

A Chain represents a configured list of Command s that will be executed in order to perform processing on a specified Context .

A Command encapsulates a unit of processing work to be performed, whose purpose is to examine and/or modify the state of a transaction that is represented by a Context .

A Context represents the state information that is accessed and manipulated by the execution of a Command or a Chain .

A Filter is a specialized Command that also expects the Chain that is executing it to call the postprocess() method if it called the execute() method.