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XPDL 2.1 Integrating Process Interchange & BPMN Robert M. Shapiro Chairman: WfMC Working Group One January 2008 White Paper

XPDL 2.1 - Integrating Process Interchange & BPMN HISTORY The basic concepts that underlie XPDL1 were formulated by individuals working together in the WfMC2 who were from companies developing workﬂ ow and business process management tools. These concepts were embodied in a meta-model and glossary which then guided the speciﬁ cation of interfaces for various aspects of the overall problem. The interchange of process deﬁ nitions between different tools and also different vendors was regarded as an essential piece of this whole and the ﬁ rst version of a standard interchange language was WPDL, published by the WfMC in November 1998. The growing popularity of XML and its use for deﬁ ning document formats for the Internet, combined with some years of accumulated experience using WPDL in workﬂ ow and BPM tools, led to the creation of XPDL 1.0, which was ofﬁ cially released in October 2002. XPDL retained the semantics of WPDL but deﬁ ned a new syntax using an XML schema. Neither WPDL nor XPDL 1.0 proposed a speciﬁ c graphical representation, although the underlying meta- model for a process was based on a directed graph structure consisting of activities as nodes and transitions as the edges or pathways between them. BPMN3 was developed by individuals working together in BPMI4 to take the techniques employed in ﬂ owcharting tools, unify and extend the graphics to express the semantics required in workﬂ ow and EAI processes. BPMN 1.0 was released in May 2004. In addition to the graphical notation, BPMN incorporated a number of speciﬁ c mechanisms for process modeling that had not yet been included in XPDL; among these in particular events and message passing between processes. XPDL 2.0 incorporated these mechanisms as well as the graphics and offered an extended meta-model that uniﬁ ed XPDL and BPMN. It was ofﬁ cially approved by the WfMC membership in October 2005. In June 2007 the OMG5 published an updated version of BPMN: version 1.1. There were numerous changes to the graphics and semantics. WfMC has incorporated these changes, along with other improvements to XPDL 2.0 based on two years in the ﬁ eld, to create XPDL 2.1. This white paper has been updated to reﬂ ect these changes. In the last section of the paper we describe BPMN Model Portability Conformance which signiﬁ cantly facilitates the interchange of process models at the design level. An appendix provides a full example of BPMN, the E-Mail Voting Process. BASICS A Business Process Model consists of a collection of processes together with the applications and resources required to perform all the steps contained in the processes. We start with a discussion of the elements in a single process. To keep things simple we focus ﬁ rst on a minimal subset of elements. • Activities (the steps in the process) • Transitions (or sequence ﬂ ow) For a complete description of the graphics, syntax and semantics refer to 6 and 7 In the diagram above. the four round rectangles are activities and the four arrows are transitions which deﬁ ne possible paths between activities. The 1 XML Process Deﬁ nition Language 2 Workﬂ ow Management Coalition 3 Business Process Modeling Notation 4 Business Process Management Initiative 3 Object Management Group wfmc.org/xpdl 2 Copyright ©2008: The Workﬂ ow Management Coalition

XPDL 2.1 - Integrating Process Interchange & BPMN leftmost activity, Receive Payment, is the ﬁ rst activity to be performed in the process since it has no predecessor. Send Receipt is the last activity. Process Large Payment and Process Small Payment are alternatives: a payment is routed to one or the other according to the amount of the payment. The Boolean expressions on the transitions determine which transition occurs, as determined by a piece of data, amount, associated with the payment. This notation is commonly employed in Petri Nets, a mathematical formalism that Inﬂ uenced the development of XPDL. Flow charts often use speciﬁ c graphical elements to indicate branching logic. To support this XPDL offers routing activities (gateways). The diagram could then be drawn as: Here the diamond shaped nodes are routing activities and the X indicates exclusive-or logic. The Exclusive Gateway on the left is a branch. Only one exit transition has a condition expression; the other path is marked as the default gate, to be taken only if the conditions on all other exit gates evaluate to false. There are a number of gateway types. For The most commonly used are: Exclusive (XOR) [Note that the ‘X’ symbol is optional] Parallel (AND) The nodes and transitions can form arbitrarily complex graphs with • Sequential Activities • Parallel Activities • Loops / Cycles • Conditional Paths 6 BPMI/OMG, BPMN (version 1.1 – June, 2007 7 WfMC, XPDL 2.1 WFMC-TC-1025 (version 1.0 April 2008 In the above ﬂ ow we have introduced a third type of activity node, an Event. An event is something that “happens” during the course of a business process. These events affect the ﬂ ow of the process and usually have a cause (trigger) or an impact (result). There are three types of Events, based on when they affect the ﬂ ow: Start, Intermediate, and End. There are numerous trigger and result types. Some common combinations are: wfmc.org/xpdl 3 Copyright ©2008: The Workﬂ ow Management Coalition

XPDL 2.1 - Integrating Process Interchange & BPMN Start Event triggered by a message. Intermediate Event triggered by a Timer. End Event with Error Result ACTIVITIES We have said nothing about the details of a basic activity. It is a step in the process, but what happens at that step? Typically, to perform a step requires one or more resources: e.g. a person with a particular skill set or a system resource. A task or application may need to be executed to perform the step. So basic activities have attributes which provide information about who can perform the activity, what application or web services should be invoked, what properties of the object being worked on are used and/or altered in this step, and so forth. The participants (resources) and applications may be deﬁ ned within a single process or for the entire collection of processes in the Business Process Model. The properties of work objects are likewise deﬁ nable within a single process or for the entire model. Activities have other attributes which further deﬁ ne their speciﬁ c role or how they are implemented. Here we list a few: • Loop • IsATransaction Activity is repeated until condition is false. Transaction-based semantics. TASKS AND APPLICATIONS There are seven standard Tasks that can be speciﬁ ed for a basic Activity and are used primarily for invoking Web Services and using WSDL8 meessaging. An eighth task type is used for invoking Applications whose signatures have been deﬁ ned in the Business Process Model. Applications that can be invoked by a process are deﬁ ned at the Process or Package (See Package meta-model) level. There are multiple types of applications: • Traditional applications • Components • Web Services • Business Rules • Form • Script 8 Web Services Description Language wfmc.org/xpdl 4 Copyright ©2008: The Workﬂ ow Management Coalition

XPDL 2.1 - Integrating Process Interchange & BPMN COMPOUND ACTIVITIES A compound activity refers to another process (reusable or embedded). The graphics for a compound activity include a special marker to designate this Compound activities allow re-use of process deﬁ nitions. If the reference is to a reusable sub-process, a list of actual parameters can be passed to the sub-process at the time of invocation. An embedded sub-process shares the same data space so no parameters are passed. (As a technical detail not shown in the graphical representation, an embedded process is an XPDL activity set and the compound activity is referred to as a Block Activity). A reusable sub-process may be invoked asynchronously, in which case the exit transitions from the compound activity immediately determine the routing of the work object to the successor of the compound activity. Synchronous invocation requires that the sub-process complete before the compound activity can continue. Embedded sub-processes are always invoked synchronously. Process MetaModel The meta-model depicts the relationships between all the elements in a Process. The shaded elements were not present in XPDL 1.0 and are now included in XPDL 2.1 to support BPMN constructs. Gateway and Event have already been described. Pool and Lane are elements that support the use of graphical Swimlanes which we discuss later in this chapter. wfmc.org/xpdl 5 Copyright ©2008: The Workﬂ ow Management Coalition

XPDL 2.0 Integrating Process Interchange & BPMN Package MetaModel This meta-model describes the relationship between elements on the Package or Business Process Diagram level. The shaded elements were not present in XPDL 1.0 and are now included in XPDL 2.1 to support BPMN constructs. wfmc.org/xpdl 6 Copyright ©2008: The Workﬂ ow Management Coalition

XPDL 2.0 Integrating Process Interchange & BPMN SWIM LANES In the following diagram we depict a single pool containing the process Loan Application. There are no lanes in the pool. The process can be either a reusable sub-process or an embedded sub-process. In the following diagram we depict a single pool containing the process Loan Application. There are no lanes in the pool. The process can be either a reusable sub-process or an embedded sub-process. Notice that the transitions (sequence ﬂ ow) may go across lanes in a pool. Transitions may not go across pools. MESSAGE FLOW Message Flow is normally implemented by Web Services and Message Queues. In the example we illustrate how message ﬂ ow may go between activities in different pools. This allows us to represent graphically aspects of the choreography between processes. It should be noted that message ﬂ ow cannot occur between activities in the same pool. In other words, sequence ﬂ ow is used to connect activities in the same pool whereas message ﬂ ow is used to represent communication between activities in different pools. In these examples pools have been drawn with a horizontal orientation and a width that extends across the entire page. However, the speciﬁ cation supports vertical pools as well, and also allows the width/height to be limited. This supports the use of pools in the speciﬁ cation of abstract processes and their choreography. wfmc.org/xpdl 7 Copyright ©2008: The Workﬂ ow Management Coalition

XPDL 2.0 Integrating Process Interchange & BPMN ARTIFACTS Artifacts provide documentation facilities with graphical representation. Associations are used to connect the artifacts to ﬂ ow objects such as activities. The association is like a sequence or message ﬂ ow, but allows optional arrows at either or both ends of the pathway. Data Object: Text Annotation: Group: Allows diverse objects to be labeled with the same name for reporting purposes. wfmc.org/xpdl 8 Copyright ©2008: The Workﬂ ow Management Coalition

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