Your starting point for this step is—naturally enough—the swimlanes that we created in the last step.

Pick an Interface

Your swimlanes from Step 3 reflect actors, interfaces, and user interfaces, so you need to select one of these as a starting point. Put an icon for it in a Component Diagram. Also, you should put the interface on a Class Diagram as a class icon with an «interface» stereotype, or you could just list it in a document. In either case, go through your swimlaned Activity Diagrams and find each place where the interface appears. Find each activity in the swimlane that is called from another swimlane, and add that activity to the interface as an operation. (If the activity has been converted so that it is now part of a subactivity state and is no longer called from outside, then you should only list the subactivity state as an operation, not its constituent activity states.)

Assign the Interface to a Component

Brainstorm and describe the component that might realize the interface. Perhaps you have a preexisting interface provided by a known, existing component. Here are some common preexisting interfaces:

• ODBC (Open Database Connectivity). A common SQL mechanism sup- ported by many databases. It might be realized by Oracle, Microsoft SQL Server, Microsoft Access, or a number of other SQL databases.

• ADO.NET. The .NET answer to common database access.

• MAPI (Messaging API). A common mechanism for accessing mail services. It might be realized by Microsoft Outlook or a number of other mail servers.

• HTTP (Hypertext Transfer Protocol). A common mechanism for document transfer on the Internet. It might be realized by Microsoft Internet Infor- mation Server (IIS), the Apache Web Server, or other Web servers.

• FTP (File Transfer Protocol). A common mechanism for file transfer on the Internet. It might be realized by Microsoft Internet Information Server (IIS) or other file servers.

• SQL (Structured Query Language). A common mechanism for storing and querying data. It might be realized by Microsoft SQL Server, Oracle DBMS, or other database servers.

Or perhaps you have already defined a new component, and believe it should provide a newly identified interface. Or perhaps your new interface will require a freshly discovered new component.

If the component (preexisting or new) isn’t already on your Component Diagram, add it as a component icon. Then connect the component to the interface via a realization line.

Repeat for Each Interface

Add all additional interfaces to the Component Diagram, and indicate which component or components realize each interface.

From the Activity Diagrams, Identify Dependencies

For each interface, examine its corresponding swimlanes in the Activity Diagrams. Look at the other swimlanes that have transitions into those swimlanes. Those transitions define dependencies: the component that realizes a “calling” swimlane is dependent upon the interface for the “called” swimlane. Add the dependencies indicated. (See the later example for more details on how to do this.)

Rearrange to Make a Legible Diagram

Consider ways to make the Component Diagram more legible:

• Try to avoid crossing lines whenever possible.

• Consider whether you may need to break the Component Diagram into multiple diagrams to show various interactions.

• Hide extraneous details in the diagrams.

Consider also that some rearrangements are worse than others. Save your work, and be ready to undo and try other approaches. Aesthetics and readability can involve a lot of trial and error.

Repeat and rearrange until you’re comfortable that you have an architecture that can fulfill the scenarios as depicted in the Activity Diagrams.

That all sounds straightforward enough, doesn’t it? Still, there’s a lot going on here, so let’s see how this all works in an example.