Patterns: Serial and Parallel Processes for Process Choreography and Workflow

152 Patterns: Serial and Parallel Processes

9.3 General design guidelines

In this scenario, it is acceptable to have a user initiate a short-running process

and await a response when the process completes. Precautions need to be

taken to ensure that the process does not stop during execution. If any

exceptions occur during the processing, the process should complete and the

response from the process should indicate that there was some form of failure.

For a short-running process, timeouts must be included on all of the activities to

ensure that the process does not get stranded.

In this Serial Process pattern scenario, there is no human intervention other than

from the order clerk who initiates the process. We can assume that the order

clerk will launch the process when he submits an order and that he will receive a

response when the order process is completed.

9.3.1 Design overview

This scenario is an implementation of the Process-focused Application

Integration::Serial Process pattern.

For information about the Serial Process Application pattern see:

3.4.6, “Serial Process Application pattern” on page 55

For information about the Serial Process Runtime pattern see:

5.1.1, “Serial Process Runtime pattern” on page 84

Process or workflow?

The term

process is used throughout this redbook to generically describe a

business process. A process may or may not contain human interaction.

The term

workflow is taken to mean a long-running process. A distinction of a

workflow or long-running process is that it persists process instance data

within the process manager’s database during the execution of the process. A

workflow may or may not include human interaction.

A

short-running process can be defined as a process that contains all

automated steps and will complete in a very short period of time. Contrary to a

long-running process, a short-running process does not persist any process

instance data. A WebSphere Process Choreographer non-interruptible

process falls into the category of a short-running process.

Chapter 9. Creating serial processes 153

For information about the Product mappings of the Serial Process Runtime

pattern see:

5.2.1, “Serial Process Product mappings” on page 93

This scenario is an implementation of Stage One of the ITSO Electronics

integration project. For information about the use case and actors used in Stage

I, see:

6.2.1, “Stage One: Internal ordering on demand” on page 110

9.3.2 Design considerations

We recommend that you consider the following design considerations when

planning any type of process implementation:

򐂰 Synchronous verses asynchronous process invocation

򐂰 The need for human interaction in processes

򐂰 Rules engines

򐂰 Security

򐂰 The impact of performance and capacity analysis

򐂰 Audit trail

Synchronous verses asynchronous process invocation

Most process managers support the two basic process invocation methods:

򐂰 synchronous invocation

򐂰 asynchronous invocation

A synchronous invocation of a process means that a response is not returned

from the process manager until the process completes (Figure 9-2 on page 154).

However, the completion of the process does not mean that it completed

successfully. The reply needs to be inspected to determine the success or failure

of the process.

154 Patterns: Serial and Parallel Processes

Figure 9-2 Synchronous process invocation

An asynchronous invocation of a process receives an immediate response, but

this response only indicates whether the process instance was started

successfully or not (Figure 9-3). Depending on the process manager, a response

may or may not be sent back to the user at the completion of the process.

Figure 9-3 Asynchronous process invocation

Choosing an invocation method

The characteristics of the two process invocation methods are used to determine

which method to choose for a given process template.

A synchronous invocation should usually be chosen when the following

circumstances are true:

򐂰 The process is short-running.

򐂰 The calling application will receive a response in a reasonable amount of

time.

򐂰 The user who has invoked the process expects to wait for a response.

Start Process

Request

Process Complete

Response

Start Process

Request

Process Started

Successfully Response