BPEL Overview

Using BPMN to Model a BPEL Process

Stephen A. White, IBM Corp., United States

ABSTRACT

The Business Process Modeling Notation (BPMN) has been developed to enable business user to

develop readily understandable graphical representations of business processes. BPMN is also

supported with appropriate graphical object properties that will enable the generation of executable

BPEL. Thus, BPMN creates a standardized bridge for the gap between the business process design

and process implementation. This paper presents a simple, yet instructive example of how a BPMN

diagram can be used to generate a BPEL process.

INTRODUCTION

The Business Process Modeling Notation (BPMN) has been developed to enable business user to

develop readily understandable graphical representations of business processes. BPMN is also

supported with appropriate graphical object properties that will enable the generation of

executable BPEL. This paper presents an example of an order shipping process, yet instructive

example of how a BPMN diagram can be used to generate a BPEL process.

When mapping a BPMN diagram to BPEL (version 1.1)1

, a decision must be made as to the basic

structure of the BPEL document. That is, will the BPEL format be based on the BPEL graph

structure (the flow element) or the BPEL block structure (the sequence element)? This choice will

affect how much of the BPMN Sequence Flow will map to BPEL link elements. Using a block

structure as the foundation for mapping, link elements only are used when there is a specific

section of the Process where parallel activities occur. Using the graph structure as the foundation

for mapping, most Sequence Flow will map to link elements, as the entire BPEL process is

contained within a flow element. Since the BPMN 1.0 specification2

takes the approach of defining

the mapping of BPMN elements to BPEL elements mainly through the use of block structures,

this paper will take the approach of using the graph structure for the mapping.

THE EXAMPLE: TRAVEL BOOKING PROCESS

The example that will be used in this paper is a basic version of a travel booking process. This

example will illustrate a few situations that occur within BPMN diagrams and how they map to

BPEL, such as parallel flow, and loops. Figure 1 shows the original representation of the BPEL

Process.3

1

http://www-106.ibm.com/developerworks/webservices/library/ws-bpel/

2

http://www.bpmi.org/bpmn-spec.htm

3

http://publib.boulder.ibm.com/infocenter/adiehelp/index.jsp?topic=

/com.ibm.etools.ctc.bpel.doc/samples/travelbooking/travelBooking.html

USING BPMNTO MODEL A BPEL PROCESS

2

Figure 1. Travel Booking Process with WebSphere Studio

Figure 2 shows how the same process can be modeled with BPMN. It could be noted that Figure 2

shows the process model laid out in a horizontal direction, going left to right, while the original

diagram in Figure 1 shows the process laid out in a vertical direction, going top to bottom. Process

tools that create strictly BPEL process tend to lay out diagrams in a vertical direction. Although

not universal, the difference between the two modeling techniques tends to separate business

analysts, who tend to opt for horizontal diagrams, and IT specialist or software developers, who

tend to opt for vertical diagrams. While BPMN doesrequire any specific directionality, most BPMN

diagrams flow horizontally.

USING BPMNTO MODEL A BPEL PROCESS

3

Figure 2. Travel Booking Process with BPMN

The Process begins with the receipt of a request for a travel booking. After a check on the credit

card, reservations are made for a flight, a hotel, and a car. The car reservation may take more

than one attempt before it is successful. After all three reservations are confirmed, a reply is sent.

Setting up the BPEL Information

BPMN Diagrams, such as the one seen in Figure 2, can be used within many methodologies and

for many purposes, from high-level descriptive modeling to detailed modeling intended for process

execution. When one of the purposes of the process model is to define process execution and

create the BPEL file for this purpose, then the process model will have to be developed with a

modeling tool designed for this purpose. The diagram itself will not display all the information

required to create a valid BPEL file. A diagram with all that information would be too cluttered to

be readable. A BPMN diagram is intended to display the basic structure and flow of activities and

data within a business process. Therefore, a modeling tool is necessary to capture the additional

information