Our intention to support interaction design is emphasized in order to delimit the scope of the paper. We are not (here) concerned with the specification of software architecture and software components and we do not assume familiarity of interaction designers with software development. Rather, we wish to investigate which subset and extensions of the UML can support the articulation of design ideas and their communication to software developers.
The task consists in three subtasks, performed in sequence. The tree describes a task where a service department of a
manufacturing company handles warrantee claims, repairs faulty products and
judges claims for warrantee cover. These activities are performed
in sequence with information flowing between them (the >> symbol).
The resolution of the complaint can be broken down to activities that are
independent of each other (the ||| symbol), one of which is optional (shown
in square brackets).
This example, does not show the full features of this notation which, it must be noted, verges on the most complex and high level notations among those proposed for task modelling, aiming to bridge the gap between the needs of the analyst and the developer. The analyst relies on the tree structure to communicate with the user, while making economical use of temporal ordering operators and the attributes associated with each task. More detail and precision is required by developers, who need the full expressive power of the notation, plus simulation tools to validate their specification.
The following activity diagram specifies the temporal sequencing of the task related activities. This diagram could be combined with a more extensive use case based task specification, as was shown in 
As mentioned in the previous section, this activity diagram does not capture
the decomposition of the task to subtasks. The intermediate nodes
of the ConcurTaskTree (Record Claim, Resolve Claim, and Arrange Payment) do not map to any activity node in
the diagram of figure2.
The required extension to the UML will allow mixing the hierarchical decomposition information with activity diagrams, as in figure 3.