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Thursday, 13 June 2013 11:09

Pattern PP4: Multi Instance Activity

This pattern allows for deferring the decision on how often a specific activity should be executed during run-time, while the activity itself needs to be predefined. PP4 not only constitutes a change pattern, but a workflow pattern as well. It allows for the creation of multiple activity instances during run-time. The decision how many instances are created can be based either on knowledge available at build-time or on some run-time knowledge. We do not consider multi-instance activities of the former kind as a change pattern as their use does not help dealing with uncertainty. For all other types of multi-instance activities the number of instances is determined based on run-time knowledge, which is or is not available a-priori to the execution of the multi-instance activity. While in the former case the number of instances can be determined at some point during run-time before executing them, this is not possible in the latter case. Multi-Instance Activities are considered as change patterns as their usage allows users to delay the decision on the number of instances to be created for a particular activity to run-time.

Description

This pattern allows for the creation of multi instances of the respective activity during run-time.

Example

The scanning activity has to be repeated until all parcels of a truck are scanned. The number of parcels is not known at build-time.

Problem

A particular activity has to be executed several times. The number of activity instances to be created is not known at build-time.

PP4

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