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38 N. Russell and A. ter Hofstede
Data Visibility Patterns

Data visibility patterns define the binding of a data element and its region of vis-
ibility. Data elements are usually defined in the context of a particular component
of a process and this binding usually defines the scope in which the data element is
both visible to and capable of being used by other process elements. There are eight
distinct patterns in this group, which describe different degrees of data scoping as
follows:
Task Data, which corresponds to a data element defined in the context of a par-
ticular task. It is typically only accessible within a given task instance and has the
same life-span as the task instance to which it is bound. The Task Data pattern
is illustrated by the variable tvar that is associated with task A in Fig. 2.8 and is
accessible only within the context of this task.
Block Data, which corresponds to a data element defined in the context of a
particular block or net within a process that is hierarchical in form. The data
element is visible throughout the block and it has a life-span corresponding to
the life-span of the block. The Block Data pattern is illustrated by the variables
bvar and bvar that are associated with the two process block depicted in Fig. 2.8.
0
bvar is accessible only by tasks in the upper block, while bvar is accessible only
0
to tasks within the lower block that corresponds to the subprocess decomposition
of task C in the upper block.
Scope Data, which corresponds to a data element bound to a set of tasks in a
process. If the process is hierarchical in form, the tasks are assumed to be in the
same block although they need not be directly connected. A scope data element
is visible only to the tasks of which the scope is comprised. It has the same life-
span as the block in which it resides. The Scope Data pattern is illustrated by the
variable svar shown in Fig. 2.8, which is accessible only by tasks B and C.

Fig. 2.8 Examples of data visibility patterns