Pattern 11 (Sub-Workflow Decomposition to Block Task)

FLASH animation of Data Interaction - Sub-Workflow Decomposition to Block Task pattern

Description

The ability to pass data elements from the underlying subprocess back to the corresponding block task. Only nominated data elements defined as part of the subprocess are made available to the (parent) block task.

Example

The Determine Optimal Trajectory subprocess passes the coordinates of the launch and target locations and flight plan back to the block task.

Motivation

At the conclusion of the underlying subprocess, the data elements which have resulted from its execution need to be made available to the block task which called it.

Overview

The approaches taken to handling this pattern are essentially the same as those identified for Data Interaction - Block Task to Subprocess Decomposition pattern (WDP-10). Where data elements are passed on an explicit basis, a mapping needs to be specified for each output parameter indicating which data element at block level will receive the relevant output value.

Context

There are no specific context conditions associated with this pattern.

Implementation

As for the Data Interaction - Block Task to Subprocess Decomposition pattern.

Issues

One difficulty that can arise with the implementation of this pattern occurs when there is not a strict correspondence between the data elements returned from the subprocess and the receiving data elements at block task level. E.g. the subprocess returns more data elements than the block task is expecting, possibly as a result of additional data elements being created during its execution.

Solutions

This problem can be solved in one of two ways. Some offerings such as Staffware support the ability for block tasks to create data elements at block task level for those data items at subprocess level which it has not previously encountered. Other products such as Websphere MQ require a strict mapping to be defined between subprocess and block task data elements to prevent this situation from arising.

Evaluation Criteria

An offering achieves full support if it has a construct that satisfies the description for the pattern. It achieves a partial support rating if it is not possible to limit the range of data elements which are passed from the subprocess to the block task.

Product Evaluation

To achieve a + rating (direct support) or a +/- rating (partial support) the product should satisfy the corresponding evaluation criterion of the pattern. Otherwise a - rating (no support) is assigned.

Summary of Evaluation