Pattern 2 (Parallel Split)

FLASH animation of Parallel Split pattern

Description

The divergence of a branch into two or more parallel branches each of which execute concurrently.

Synonyms

AND-split, parallel routing, parallel split, fork.

Examples

After completion of the capture enrolment task, run the create student profile and issue enrolment confirmation tasks simultaneously.

When an intrusion alarm is received, trigger the despatch patrol task and the inform police task immediately.

Once the customer has paid for the goods, pack them and issue a receipt.

Motivation

The Parallel Split pattern allows a single thread of execution to be split into two or more branches which can execute tasks concurrently. These branches may or may not be re-synchronized at some future time.

Overview

Figure 2 illustrates the implementation of the Parallel Split. After task A has completed, two distinct threads of execution are initiated and tasks B and C can proceed concurrently.

Figure 2: Parallel split pattern

Context

There are no specific context conditions for this pattern.

Implementation

The Parallel Split pattern is implemented by all of the offerings examined. It may be depicted either explicitly or implicitly in process models. Where it is represented explicitly, a specific construct exists for the Parallel Split with one incoming edge and two or more outgoing edges. Where it is represented implicitly, this can be done in one of two ways: either (1) the edge representing control-flow can split into two (or more) distinct branches or (2) the task after which the Parallel Split occurs has multiple outgoing edges which do not have any conditions associated with them or where it does these conditions always evaluate to true.

Of the offerings examined, Staffware, WebSphere MQ, FLOWer, COSA and iPlanet represent the pattern implicitly. SAP Workflow, EPCs and BPEL do so with explicit branching constructs. UML 2.0 ADs, BPMN and XPDL allow it to be represented in both ways.

Issues

None identified.

Solutions

N/A.

Evaluation Criteria

Full support for this pattern is demonstrated by the provision of a construct (either implicit or explicit) that allows the thread of control at a given point in a process to be split into two or more concurrent branches.

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.