Pattern 11 (Implicit Termination)

FLASH animation of Implicit Termination pattern

Description

A given process (or sub-process) instance should terminate when there are no remaining work items that are able to be done either now or at any time in the future and the process instance is not in deadlock. There is an objective means of determining that the process instance has successully completed.

Synonyms

None.

Examples

N/A.

Motivation

The rationale for this pattern is that it represents the most realistic approach to determining when a process instance can be designated as complete. This is when there is no remaining work to be completed as part of it and it is not possible that work items will arise at some future time.

Overview

N/A.

Context

There are no specific context considerations associated with this pattern.

Implementation

Staffware, WebSphere MQ, FLOWer, FileNet, BPEL, BPMN, XPDL, UML 2.0 ADs and EPCs support this pattern. iPlanet requires processes to have a unique end node. COSA terminates a process instance when a specific type of end node is reached.

Issues

Where an offering does not directly support this pattern, the question arises as to whether it can implement a process model which has been developed based on the notion of Implicit Termination.

Solutions

For simple process models, it may be possible to indirectly achieve the same effect by replacing all of the end nodes for a process with links to an OR-join which then links to a single final node. However, it is less clear for more complex process models involving multiple instance tasks whether they are always able to be converted to a model with a single terminating node. Potential solutions to this are discussed at length by Kiepuszewski et al. [KtHvdA03].

It is worthwhile noting that some languages do not offer this construct on purpose: the Implicit Termination pattern makes it difficult (or even impossible) to distinguish proper termination from deadlock. Often it is only through examination of the process log that it is possible to determin if a particular case has actually finished. Additionally, processes without explicit endpoints are more difficult to use in compositions.

Evaluation Criteria

An offering achieves full support if it is possible to have multiple final nodes and the behaviour of these nodes satisfies the description for the pattern.

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.