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5.2 Nodes
A node is a resource that
is available during
execution time. (Nodes were mentioned in Chapter 2.) Traditionally, nodes refer to computers on a
network, but in the UML a node may be a computer, printer, server,
Internet, or any other kind of resource available to components. For
example, the project management system may be deployed on the
following nodes:
A desktop client
On which the user interface
component executes
A printer
Which the project management
system
uses to print reports
A business-processing server
On which the business-processing
component executes
A database server
On which the data component
executes and where project-related
information is stored
Nodes follow the type-instance dichotomy first discussed in Chapter 2 and applied to classes and objects in Chapter 3. You can use the UML to talk about classes of
nodes, as well as specific nodes of a class. When speaking of a class
of nodes, it's customary to use the terms node or
node class. Thus,
while you might think of a node as a
specific thing, in the UML, a node really represents a class of
nodes. When speaking of a specific component of a class, use the
term node
instance.A node is available during execution time and is a resource on which
components may execute. In the UML, a node is shown as a
three-dimensional rectangle labeled with the node's
name.Figure 5-3 shows various nodes associated with the
project management system, including a desktop client,
business-processing server, database server, and printer node.
Figure 5-3. Nodes used by the project management system
A node instance is a specific node. For example, specific nodes used
by the project management system include:
A desktop client node instance
Used by Jonathan to access the project management system
A desktop client node instance
Used by Andy to access the project management system
A group business-processing server node instance
Used by a group of users to manage
projects
An enterprise business-processing server node instance
Used by a complete organization to manage projects
A node instance is shown similarly to a node class but labeled with
the node instance name followed by a colon followed by the node class
name, all fully underlined. Both names are optional, and the colon is
present only if the node class name is specified.Figure 5-4 shows various node instances of the node
classes in Figure 5-3, including two desktop client
node instances, named Jonathan's Computer and
Andy's Computer, two business-processing node
instances, named Group Server
and Enterprise Server, a
printer node instance, named Group Printer, and a
database server node instance.
Figure 5-4. Node instances
