Patterns: Building Serial and Parallel Processes for IBM WebSphere Process Server V6

Chapter 4. Application Integration and Extended Enterprise patterns 53

4.1.2 Serial Process application pattern

The Serial Process application pattern, shown in Figure 4-2, supports the

sequential execution of business services hosted by a number of target

applications. The source application initiates a serial business process.

Figure 4-2 Serial Process application pattern

Business and IT drivers

The primary business driver for this pattern is composing a set of business

services into an end-to-end business process.

From an IT perspective, the key driver is improving the flexibility and

responsiveness of IT by externalizing the process flow logic from individual

applications.

Solution

The Serial Process application pattern is broken down into three logical tiers:

򐂰 The Source Application tier represents one or more applications that are

interested in interacting with the target applications.

򐂰 The Serial Process Rules tier supports most of the services provided by the

broker tier in the Broker application pattern, including routing of requests,

protocol conversion, message broadcasting, and message decomposition/

recomposition. It also supports the separation of business process flow logic

from individual application logic.

The process logic is governed by the serial process rules that define

execution rules for each target application, together with control flow and data

Source

Application

Serial Process

Rules Tier

Target

Application

Target

Application

Target

Application

R/O

WIP

Intermediate

Results

Process

Execution Rules

54 Patterns: Building Serial and Parallel Processes for IBM WebSphere Process Server V6

flow rules. It may also include any necessary adapter rules. The combination

of these process execution rules are stored in read-only databases.

This externalization of process flow logic is essential for the implementation of

a flexible and responsive IT environment that can respond quickly to changing

business needs. It also makes it possible to compose new end-to-end

processes by combining different business services provided by different

applications. Finally, this tier uses a work-in-progress (WIP) database to store

the intermediate results from the execution of different process steps.

򐂰 The Target Application tier represents new, modified existing, or unmodified

existing applications that implement the necessary business services.

Guidelines for use

The flexibility and responsiveness provided by this Application pattern depend on

externalizing process execution logic from individual applications. Applications

designed with a service-oriented architecture (SOA) approach, which have

well-defined and coarse-grained business services, are better suited for

participation in this pattern. A service may participate in more than one

end-to-end process.

Typically, traditional applications are not designed with this approach in mind.

Moreover, many have significant amounts of process logic embedded within

them. These constraints in existing environments may pose challenges to fully

implementing this Application pattern. A good starting point is to wrap traditional

and packaged applications into business services.

Composing process flows by tying together different applications may introduce

the need for compensating transaction support. This is especially true when

participating applications do not leverage XA-compliant transaction processing

engines. You may need to design compensating transaction pairs for every

affected transaction. You may also need to modify participating traditional and

packaged target applications to introduce compensating transactions.

Finally, pay particular attention to the business process management capabilities

supported by the business process design tools and the process execution

engines when you select middleware products. The goal is to enable business

users to compose business processes and make necessary changes with

minimal involvement from IT professionals. The business processes thus defined

must be easily exported into a process execution engine. More sophisticated

business process management tools allow for the definition of metrics during

process design and support monitoring of the metrics in the process execution

engine.

Chapter 4. Application Integration and Extended Enterprise patterns 55

Benefits

The Serial Process application pattern improves the flexibility and

responsiveness of an organization by implementing end-to-end process flows

and by externalizing process logic from individual applications.

򐂰 It integrates multiple, diverse applications.

򐂰 It minimizes the impact to existing applications.

򐂰 It relieves the source application from being aware of the target application.

򐂰 It can provide transformation services that allow the source and target to use

different communication protocols.

򐂰 It minimizes the impact of changes in location of the target application.

򐂰 It provides a foundation for automated support for business process

management, enabling monitoring and measurement of the effectiveness of

business processes.

Limitations

This Application pattern supports straight-through processing without human

interaction. If human interaction is needed to complete certain process steps,

consider the Workflow variation of this Application pattern as described in 4.1.4,

“Serial Workflow variation” on page 58.

It also does not support the parallel execution of multiple tasks. Under such

circumstances, consider the Parallel Process application pattern discussed in

4.1.3, “Parallel Process pattern” on page 56.