Event-driven process chain
Businesses use EPC diagrams to lay out business process work flows, originally in conjunction with
SAP R/3modeling, but now more widely. There are a number of tools for creating EPC diagrams, including ARIS Toolset of [http://www.ids-scheer.com/ IDS Scheer AG] , ADONIS of [http://www.boc-group.com/ BOC Group] , Visio of Microsoft Corp., Semtalk of Semtation GmbH, or Bonapart by Pikos GmbH. Some but not all of these tools support the tool-independent EPC Markup Language ( EPML) interchange format. There are also tools that generate EPC diagrams from operational data, such as SAP logs. EPC diagrams use symbols of several kinds to show the control flow structure (sequence of decisions, functions, events, and other elements) of a business process.
The EPC method was developed within the framework of ARIS by Prof. Wilhelm-August Scheer at the Institut für Wirtschaftsinformatik at the Universität des Saarlandes in the early 1990s. It is used by many companies for modeling, analyzing, and redesigning business processes. As such it forms the core technique for modeling in ARIS, which serves to link the different views in the so-called control view, which will be elaborated in section of ARIS Business Process Modeling.
To quote from a publication on EPCs: [ [http://ieeexplore.ieee.org/iel5/4273787/4274280/04274298.pdf?tp=&isnumber=4274280&arnumber=4274298&ei=IJVvSMn_OIrIQYnZrNQC&usg=AFQjCNFJBVEWjT3T94GTCVjGYSopT3pCAw&sig2=vRB5_Wj_tzW1BCR6wbhiBg "EPC Workflow Model to WIFA Model Conversion", by Anni Tsai, Jiacun Wang William Tepfenhart and Daniela Rosen, in: "2006 IEEE International Conference on Systems, Man, and Cybernetics, Taipei, Taiwan", pp. 2758-2763] ] "An EPC is an
ordered graphof events and functions. It provides various connectors that allow alternative and parallel execution of processes. Furthermore it is specified by the usages of logical operators, such as OR, AND, and XOR. A major strength of EPC is claimed to be its simplicity and easy-to-understand notation. This makes EPC a widely acceptable technique to denote business processes."
The statement that EPCs are ordered graphs is also found in other literature, but is probably a misformulation: an ordered graph is a(n undirected) graph with an explicitly provided total node ordering, while EPCs are
directed graphs for which no explicit node ordering is provided. No restrictions actually appear to exist on the possible structure of EPCs, but nontrivial structures involving parallellism have ill-defined execution semantics; in this respect they resemble UML activity diagrams. Several scientific articles are devoted to providing well-defined execution semantics for general EPCs. [ [http://is.tm.tue.nl/staff/wvdaalst/publications/p74.pdf "Formalization and Verification of Event-driven Process Chains", by Wil van der Aalst] ] [ [http://www.win.tue.nl/~ooanea/papers/HOSCoopIS05.pdf "Colored Petri Nets to Verify Extended Event-Driven Process Chains", by Kees van Hee, Olivia Oanea, Alexander Serebrenik, Natalia Sidorova and Marc Voorhoeve, in "Proc. of the 4th Workshop on Modelling, Simulation, Verification and Validation of Enterprise Information Systems (MSVVEIS06)", May 23-24, 2006 Paphos, Cyprus, pp. 76-85] ] One particular issue is that EPCs require non-local semantics, [ [http://www.upb.de/cs/kindler/Publikationen/copies/tr-ri03.pdf On the Semantics of EPCs: A Framework for Resolving the Vicious Circle] ] , i.e., the execution behavior of a particular node within an EPC may depend on the state of other parts of the EPC, arbitrarily far away.
In the following the elements used in EPC diagram will be described:
Elements of an Event-driven Process Chain
Events are passive elements in EPC. They describe under what circumstances a function or a process works or which state a function or a process results in. Examples of events are “requirement captured”, “material on stock”, etc. In the EPC graph an event is represented as hexagon. In general, an EPC diagram "must" start with an event and end with an event.
Functions are active elements in EPC. They model the tasks or activities within the company. Functions describe transformations from an initial state to a resulting state. In case different resulting states can occur, the selection of the respective resulting state can be modeled explicitly as a decision function using logical connectors. Functions can be refined into another EPC. In this case it is called hierarchical function. Examples of functions are “capture requirement”, “check material on stock”, etc. In the EPC graph a function is represented as rounded rectangle.
Organization units determine which person or organization within the structure of an enterprise is responsible for a specific function. Examples are “sales department”, “sales manager”, “procurement manager”, etc. It is represented as an ellipse with a vertical line.
Information, material, or resource object
In the EPC, the information, material, or resource objects portray objects in the real world, for example business objects, entities, etc., which can be input data serving as the basis for a function, or output data produced by a function. Examples are “material”, “order”, etc. In the EPC graph such an object is represented as rectangle.
In the EPC the logical relationships between elements in the control flow, that is, events and functions are described by logical connectors. With the help of logical connectors it is possible to split the control flow from one flow to two or more flows and to synchronize the control flow from two or more flows to one flow.There are three kinds of logical relationships defined in EPC:
Branch and merge correspond to making decision of which path to choose among several control flows. A branch may have one incoming control flow and two or more outgoing control flows. When the condition is fulfilled, a branch activates exactly only one of the outgoing control flows and deactivates the others.
The counterpart of a branch is a merge. A merge may have two or more incoming flows and one outgoing control flow. A merge synchronizes an activated and the deactivated alternatives. The control will then be passed to the next element after the merge. A branch in the EPC is represented by an opening XOR, whereas a merge is represented as a closing XOR connectors.
Fork and join correspond to activating all paths in the control flow concurrently. A fork may have one incoming control flow and two or more outgoing control flows. When the condition is fulfilled, a fork activates all of the outgoing control flows in parallel. A join may have two or more incoming control flows and one outgoing control flow. A join synchronizes all activated incoming control flows. In the EPC diagram how the concurrency achieved is not a matter. In reality the concurrency can be achieved by true parallelism or by virtual concurrency achieved by interleaving. A fork in the EPC is represented by an opening ‘AND’, whereas a join is represented as a closing ‘AND’ connectors.
An ‘OR’ relationship corresponds to activating one or more paths among control flows. An opening ‘OR’ connector may have one incoming control flow and two or more outgoing control flows. When the condition is fulfilled, an opening ‘OR’ connector activates one or more control flows and deactivates the rest of them. The counterpart of this is the closing ‘OR’ connector. When at least one of the incoming control flows is activated, the closing ‘OR’ connector will pass the control to the next element after it.
A control flow connects events with functions, process paths, or logical connectors creating chronological sequence and logical interdependencies between them. A control flow is represented as a dashed arrow.
Information flows show the connection between functions and input or output data, upon which the function reads changes or writes.
Organization unit assignment
Organization unit assignments show the connection between an organization unit and the function it is responsible for.
Process paths serve as navigation aid in the EPC. They show the connection from or to other processes. The process path is represented as a compound symbol composed of a function symbol superimposed upon an event symbol. To employ the process path symbol in an EPC diagram, a symbol is connected to the process path symbol, indicating that the process diagramed incorporates the entirety of a second process which, for diagramatic simplicity, is represented by a single symbol.
As shown in the example, customer order received as the initial event, which creates a requirement capture within the company. In order to specify this function, sales is responsible for marketing, currency etc. As a result, event ‘requirement captured’ leads to another new function: check material on stock, in order to manufacture the productions. All input or output data about material remains in the information resource. After checking material, two events may happen-with or without material on stock. If positive, get material from stock; if not, order material from suppliers. Since the two situations cannot happen at the same time, XOR is the proper connector to link them together.
Meta-model of EPC
Although a real process may include a series of stages until it is finished eventually, the main activities remain similar. An event triggers one function; as well function will lead to one event. Meanwhile, an event may involve only one or more processes to fulfill, but process is unique for one event, the same goes Process and Process Path. As for function, its data may be included in one or more information resources, while Organization Unit is only responsible for one specific function.
* [http://dia-installer.de/shapes/edpc/ Symbols for drawing Event-driven process chain diagrams]
* [http://www.tekom.de/index_neu.jsp?url=/servlet/ControllerGUI?action=voll&id=285 Event-driven process chains for better flows]
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