Figure 5-3 shows nodes associated with the project management system, but how are those nodes related? A specialized type of association, called a communication association, addresses the question of how nodes are related. (Associations are discussed in Chapter 3.)
A communication association between nodes indicates a communication path between the nodes that allows components on the nodes to communicate with one another. A communication association is shown as a solid-line between nodes. Figure 5-12 shows that the Business-Processing Server has a communication association with the Desktop Client, Printer, and Database Server nodes.
Figure 5-13 combines Figure 5-8 and Figure 5-12 to show how components are related to nodes. Notice that if two components are related and reside on different nodes, the nodes must have a communication association between them to allow the components to communicate; otherwise, the components are not able to communicate and be related to one another. For example, if the communication association between the Desktop Client and Business-Processing Server nodes was removed, the User Interface component could not be related to the IBusiness Processing interface and Security component. If the communication association between the Business-Processing Server and Database Server nodes was removed, the Data component could not be related to the Security component, and the Business Processing component could not be related to the IProducible and IConsumable interfaces.