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Introduction to Business Process Execution Language (BPEL)

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Business Process Execution Language (BPEL) was developed as part of a cooperative initiative by IBM, BEA, and Microsoft. This XML-based language is basically a combination of IBM's Web Services Flow Language (WSFL) and Microsoft's XLang. The resulting language is also known as BPEL for Web Services, or BPEL4WS.

BPEL4WS is a means by which to link Web services together into a single business process. The BPEL process contains a series of steps called "activities." The table below contains a list of primitive activities supported by BPEL4WS. These primitive activities allow the BPEL process to communicate with other partner services.

Primitive Activities
Activity
Description
Invokes an operation on a Web service
Waits to receive a request for an operation to be invoked by an external requester
Replies to an I/O operation
Copies data
No operation performed
Terminates the service instance
Throws an error condition
Waits for a specified amount of time


The basic roles of the BPEL process are to invoke services using the activity and to receive and reply to invocation requests from clients using the and activities. The activity assigns a value to a variable. The activity is equivalent to a "no-op" statement. The activity ends an instance of the BPEL process. The activity generates a fault condition within the BPEL process. The activity is used to insert a delay, either in intervals or until a specified time, within the process.

In addition to these primitive activities, BPEL4WS also supports a set of structure activities that, when combined with the primitive activities, allow for the creation of more complex processes. A list of the structure activities is shown in the table below.

Structure Activities
Activity
Description
Defines activities to be performed concurrently
Executes an alternate path
Defines a sequence of steps
Allows for branching control
Defines a loop


These activities give more detailed control over the BPEL process flow as an IF or CASE statement might in traditional programming languages. The activity defines one or more activities to be performed concurrently. This can be used, for example, to invoke two Web services at once. The activity waits for either an acceptable message to be received or a specified timeout to occur and performs a specific series of activities based on which of the two occurs. The activity defines a series of other activities to be performed in sequential order. The activity acts similarly to a SELECT/CASE statement sequence in traditional programming languages. It is used to select a single set of activities to perform from a group of possible conditions. Again similar to statements found in other programming languages, the activity allows a user to define a loop to be continually performed while the specified condition evaluates to "true."

Swing Your Partner

Services and clients that interact with BPEL processes are referred to as "partners." Partners can include services that are invoked by the process, services that invoke the process, and services that invoke the process and are invoked by the process. This means that a client service may invoke a BPEL process and, as a result, may be invoked itself by that process. By the same token, a BPEL process may invoke a service that in turn invokes the BPEL process. For example, a given BPEL process may invoke a service that at some later point will invoke the BPEL process to return the required data. It's important to note that the service invoked may be a Web service internal to your organization or a service hosted by an external partner (a vendor or customer, for example). Figure 1 shows an example of a simple supply chain-based BPEL process.

http://www.mcpressonline.com/articles/images/2002/BPELArticleV4--06210600.jpg
Figure 1: Here's an example of a simple supply chain BPEL process. (Click image to enlarge.)

In this example, a customer order Web service initiates the BPEL supply chain process. This process forwards the order information to the company's internal inventory/warehouse service. This service determines stock availability and sends back either a shipment confirmation message or an out-of-stock message. If the item ordered is out of stock, the BPEL process forwards the order to an external vendor's Web service. When the vendor ships the order to the customer, the vendor's Web service in turn sends a shipment confirmation back to the BPEL process. Once the order has been shipped, the BPEL process forwards the confirmation message back to the customer order system's Web service. This simple example helps to illustrate the interaction of multiple Web services into a single business process.

Software Resources

Many tools are available to help you to build BPEL processes. IBM's BPEL tool offering is Business Process Execution Language for Web Services Java Run Time (BPWS4J). BPWS4J uses a SOAP interface to make the BPEL4WS document available as a Web service. In addition, BPWS4J includes a plug-in to give you the ability to edit BPEL4WS files inside of Eclipse. BPWS4J is compatible with the Apache and Tomcat Web servers. Microsoft includes support for BPEL processes within its BizTalk Server product. Microsoft also has support for designing and implementing BPEL documents within its Visio tool and Visual Studio.Net, both of which can be used to design a business process and output a BPEL document. The resulting BPEL document is then executed within the BizTalk Server. Active Endpoints, Inc. (AEI) offers an open-source BPEL solution called ActiveBPEL engine. ActiveBPEL engine offers full support for BPEL4WS 1.1 specifications. This open-source product is incorporated in several other commercial products offered by AEI. This helps ensure commitment to the development of the open-source product. Oracle has a BPEL solution called Oracle BPEL Process Manager. Like the others, this product offers full support for BPEL 1.1, as well as an easy-to-use visual designer.

Improving Supply Chain Management with BPEL

By extending XML Web services in this manor, supply chain management is greatly improved by the ability to automate the physical business processes that are already occurring. The standards-based approach of BPEL eliminates the use of proprietary languages to build your business process, and the number of heavy hitters in the software industry offering BPEL solutions only helps to emphasize the role that this technology is poised to take.

Mike Faust is a Business Analyst for Invivo Corporation in Orlando, Florida. Mike is also the author of the books The iSeries and AS/400 Programmer's Guide to Cool Things and Active Server Pages Primer and SQL Built-in Functions and Stored Procedures. You can contact Mike at This email address is being protected from spambots. You need JavaScript enabled to view it..

Mike Faust

Mike Faust is a senior consultant/analyst for Retail Technologies Corporation in Orlando, Florida. Mike is also the author of the books Active Server Pages Primer, The iSeries and AS/400 Programmer's Guide to Cool Things, JavaScript for the Business Developer, and SQL Built-in Functions and Stored Procedures. You can contact Mike at This email address is being protected from spambots. You need JavaScript enabled to view it..

MC Press books written by Mike Faust available now on the MC Press Bookstore.

Active Server Pages Primer Active Server Pages Primer
Learn how to make the most of ASP while creating a fully functional ASP "shopping cart" application.
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JavaScript for the Business Developer JavaScript for the Business Developer
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