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The Message Rules Engine will be the software component that applications interact with to retrieve messages. An app will supply a domain, a context, and a set of input data. It will receive a list of messages appropriate for the domain and context.
Sequence Diagram
The sequence diagram shows how the components of the message rules engine interact and how an application (e.g. Online Reg) interacts with the engine. 
1. The app calls the "gatherMessages" method of the Message Rules Engine, supplying domain and context.
2. The rules engine retrieves rules metadata from the Message Rules service, based on the supplied domain and context. The metadata is a list of rules to be executed, and the associated messages.
3. The rules engine then works through the rules metadata list, evaluating each rule in the list, and constructing a list of messages returned by each rule.
4. Finally the rules engine returns the completed list of messages to the calling application.
Class Diagram
The class diagram shows the Java objects and their relationships, organized by package. 