The Action Sequence is an XML document that defines the smallest complete task that the solution engine can perform. It is executed by a very lightweight process flow engine and defines the order of execution of one or more the components of the Pentaho BI Platform. We avoid calling this a process flow because it is missing many of the capabilities of a true process flow engine. It is good for sequencing small, linear, success oriented tasks like reporting and bursting. It has the ability to loop through a result set, call another Action Sequence and conditionally execute components. The Action Sequence document should have a ".xaction" suffix.
The process of creating, and editing action sequences can be tedious at best, and the process of manually editing the action sequence XML can be error prone. The Pentaho Action Sequence editor is a standalone tool that facilates the creation and management of action sequences using a graphical interface that doesn't require knowledge or manipulation of the underlying XML. However, to better grasp the Pentaho architecture we encourage you take a peek at the section which describes the action sequence XML. Then move on to the Getting Started with Design Studio to learn more about the Pentaho Design Studio and the Action Sequence Editor, which should be your tool of choice when creating, editing, and managaging action sequences.