Scientific Journals

Zeszyty Naukowe

Maritime University of Szczecin

Akademia Morska w Szczecinie

2013, 34(106) pp. 79–84 ISSN 1733-8670

2013, 34(106) s. 79–84

Linking EPC models – an alternative approach Bartosz Szczęśniak Silesian University of Technology, Institute of Production Engineering Department of Quality Management of Process and Product 41-800 Zabrze, ul. Roosevelta 26, e-mail: [email protected] Key words: hierarchical EPC models, business process modelling Abstract Even though the literature is abundant in numerous studies concerning syntactic and semantic principles of the EPC model development, one may still have certain doubts when linking such models with one another. This article primarily addresses the principles of creating EPC models, particularly those relevant from the perspective of linking them, identified based on the literature research. What follows the said analysis is a proposal of an alternative concept which may be adopted in this respect. The author has discussed the cases in which models must be subject to specific modifications in order for the linking solution proposed to be applicable.

Introduction

problem of errors occurring in EPC models. And despite the common opinion that EPC models are fairly easy to apply, there are still many errors, both syntactic and semantic ones, encountered in the actual models applied by companies. This particular issue has been most extensively addressed by J. Mendling [15]. It has also been referred to in papers [11, 13, 16, 17, 18]. Although the subject of EPC models is very widely discussed in the literature, there may certain doubts arising with regard to the problem of their linking. This fact has encouraged the author to pursue an alternative concept to be proposed in this respect.

Even though the concept of EPC models is more than 20 years old, it is still considered to be one of the leading methodologies of economic process modelling. It was developed by scientists representing the Institute for Business Informatics at the University of Saarbrücken in collaboration with SAP AG, and it was originally presented in 1992 by G. Keller, M. Nüttgens and W. Scheer [1]. The works conducted in the subsequent years were aimed to make the rules applied wile creating EPC models more precise. Formal syntax principles for flat EPC diagrams were proposed in 1999 in a publication by W. van der Alst [2]. These formalised principles of creating both flat and hierarchical EPC diagrams were then discussed in a publication of 2002 by M. Nüttgens and F.J. Rump [3]. Modified and detailed principles applicable to hierarchical EPC diagrams were described by V. Gruhn and R. Laue [4] in 2007. The rules of EPC syntax have also been discussed in such publications as [5, 6, 7, 8]. In Polish papers, the same principles were addressed in an informal manner in publications [9, 10, 11, 12, 13]. Besides the syntax, another significant topic raised in the literature of the subject has been the semantics of EPC models [3, 5, 6, 8, 14]. Numerous authors are also interested in the Zeszyty Naukowe 34(106)

Principles of linking EPC models Article [3] provides a very thorough description of the principles applied to create flat EPC models. It also addresses the rules of their linking. They are very restrictive to a certain extent. For instance, it is impermissible to develop sequences of links where looping occurs. On the other hand, they leave some space for numerous ambiguities. Doubts may primarily arise with regard to the occurrence of process interfaces, both the triggering and the triggered ones, events preceding and following interfaces, as well as correlations between these elements. Accurate principles of establishing links between EPC 79

Bartosz Szczęśniak

models along with certain liberalisation of the prohibition to use loops to link EPC models have all been described in article [4]. However, in accordance with the solution proposed, in order to link models, one must create within them, based on a specific algorithm, an additional sphere for the transfer of logic which is disregarded while combining models into a single EPC model. Consequently, in various EPC models linked with one another, the same event may be interfaced with other elements. Striving to avoid the aforementioned inconveniences, an attempt was made by the author to propose an alternative EPC model linking concept. What remains in the focus in the following sections of the article is the overall body of problems involved in linking equivalent models by means of process interfaces. Assuming that a graphical representation of an EPC model is an EPC diagram, based on papers [2, 3, 4], one may establish the principles governing the development of such diagrams, relevant from the perspective of linking them. According to the said principles: 1. An EPC diagram consists of such elements as: functions, events, logical connectors and process interfaces. 2. All elements are interlinked by means of arrows depicting the process path. 3. Each function has exactly one incoming and one outgoing arrow. 4. Each event has: • exactly one incoming and one outgoing arrow, or • exactly one incoming arrow, when it is the end event, or • exactly one outgoing arrow, when it is the start event. 5. A process interface may have: • exactly one incoming arrow, when it is the end process interface, or • exactly one outgoing arrow, when it is the start process interface. 6. A function may be linked with events only. 7. A process interface may be linked with events only. 8. An event may be linked with a function or a process interface. 9. A link between functions, events and process interfaces may be direct or indirect, the latter using logical connectors. 10. A logical connector may be: • split connector – having exactly one incoming arrow and several outgoing arrows; • join connector – having several incoming arrows and exactly one outgoing arrow.

11. Preceding events for a process interface are events occurring before the end process interface, disregarding all the logical connectors present in the link. Preceding events may also be considered with reference to a function. A sample preceding event has been depicted in figure 1. E1 – preceding event for process interface P1

E1

E2, E3, E4 – preceding events for process interface P2

E2

E3

E4

XOR

XOR

P1

P2

Join connectors to be disregarded

Fig. 1. Sample preceding event for a process interface

12. Following events for a process interface are events whose preceding element is a start process interface. Following events may also be considered with reference to a function. A sample following event has been depicted in figure 2. P3

Split connectors to be disregarded

P4

E5 E5 – following event for process interface P3

E6

E7

E8 E6, E7, E8 – following events for process interface P4

Fig. 2. Sample following event for a process interface

13. If there an end process interface in diagram EPC1 pointing towards diagram EPC2, then there must be a start process interface in diagram EPC2 pointing towards diagram EPC1. 14. If there a start process interface in diagram EPC2 pointing towards diagram EPC1, then there must be an end process interface in diagram EPC1 pointing towards diagram EPC2. 15. In the situations referred to in items 13 and 14, the preceding events for an end process interface in the triggering diagram must conform 80

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Linking EPC models – an alternative approach

with the following events for a start process interface in the triggered diagram. 16. If a loop is formed by a group of EPC diagrams due to the links established by means of interfaces, it must feature at least one start event and one end event. A graphical illustration of this principles has been provided in figure 3. Process P1

P3 E1 F1

Process P2

Process P3

P1

E5 – start event – at least one being required

P2

E2

E5

E3 XOR

F1

F1

XOR

E2 P2

interface is linked with events by means of logical connectors. Whenever such a interface is used, the triggered diagram will consist of two parts:  the logic transfer part, and  the executed part. No functions may occur in the logic transfer part. In this part of the triggered diagram, one should include all events preceding the end process interface in the triggering diagram. The logical connectors used in the logic transfer part must recreate the logic of connections between individual events in the triggering diagram. In accordance with the algorithm proposed, split connectors are not used in this part. Linking individual events with the start process interface may be achieved in a twofold manner. The first method is a direct linking of each event with a separate start process interface. The second method involves linking all events with a single start process interface by means of logical connectors which form a link being a mirror image of the link logic previously recreated. A sample application of Type 2 process interfaces assuming the first and the second method of event linking with the start process interface has been depicted in figure 4. When using the first method, one must bear in mind that individual P1 process interfaces may not be identical. If the distinguishing feature was the name, every single interface would need a separate name. Developing one flat EPC diagram based on two linked diagrams is achieved by disregarding the logic transfer part from the triggered diagram and substituting the executed part instead of the end process interface from the triggering diagram.

E3

E1

E4 E4 – end event – at least one being required

P3

P1

Fig. 3. Start and end events required in a group of EPC diagrams forming a loop

As far as the detailed principles of linking start and end process interfaces, as well as the events preceding and following the former, V. Gruhn and R. Laue [4] have proposed to introduce and separately consider two types of process interfaces, i.e. “Type 1” and “Type 2”. A Type 1 process interface is linked directly with one event without any connectors. While linking diagrams by means of such interfaces, no doubts may occur. It is absolutely explicit what event should precede an end process interface and which one should follow the corresponding start process interface. A Type 2 process

METHOD 1 Process P1

E3

E3

METHOD 2

Process P2

Process P2

P1

P1

P1

E2

E3

E4

P1

E4 XOR

XOR

E2

XOR

P2

Split connector disregarded when recreating the logic links

F1

Logic transfer part

Executed part

Fig. 4. EPC diagram linking using a Type 2 process interface

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E3

XOR

F1

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Alternative concept

Proper events

In the following sections of the article, the author has described his own concept of linking equivalent EPC diagrams by means of process interfaces. The governing principle of the concept proposed, being a certain limitation in terms of the EPC syntax, is linking by means of process interfaces directly related with events exclusively. Hence the following rules must be observed: 17. An end process interface must have exactly one preceding event. 18. A start process interface must have exactly one following event. 19. If there an end process interface in diagram EPC1, linked with event E and pointing towards diagram EPC2, then there must be a start process interface linked with event E in diagram EPC2 pointing towards diagram EPC1. The link may be achieved by introducing a specific number of process interfaces into the EPC diagram, so that every process interface is linked with one event. Assuming that distinguishing between individual EPC diagram elements is handled based on unique names, then names of individual process interfaces must differ. Further assuming that the main purpose of linking EPC diagrams is to represent pieces of a more elaborate flat EPC diagram in separate EPC diagrams, in order to find out how individual diagrams should look like, one may begin with a flat one. Not every flat EPC diagram may be divided into several smaller linked diagrams in the manner proposed. Under certain circumstances, such a diagram should first be modified by:  introducing an additional apparent function and an apparent event linked with the former (where the apparent function may assume the form of “Send ‘Start’ signal for process ‘X’”, for instance);  splitting the event into several partial events. For the sake of establishing cases which would require modification, the following definitions are introduced: a proper event and a shared event. 20. A proper event for an end process interface is a preceding event for this process interface, which is not a preceding event for any other process interface, nor any function. 21. A shared event for an end process interface is a preceding event for this process interface, which is simultaneously a preceding event for another process interface or function. Examples of proper events and shared events have been depicted in figure 5.

E2

E3

Shared events

E4

E5

E6 F1

XOR

P2

P2

P3

P4

P5

Fig. 5. Sample proper events and shared events

Having an overall flat EPC diagram assumed to be divided into several smaller linked EPC diagrams, one may establish the diagrams to which individual elements will belong. One can also determine the events at which splitting is to take place. Then, for each of the target diagrams, one may enter hypothetical end process interfaces after the events identified. While distinguishing linked EPC diagrams and modifying the primary EPC diagram, the following principles must be followed: 22. When all preceding events for hypothetical end process interfaces are proper events, and for each of these events the functions preceding them are ultimately to be found in the same EPC diagram, there is no need to modify the flat diagram, and for the sake of process linking, one may use a sufficient number of process interfaces – a situation illustrated in figures 6 and 7. Elements to be found in EPC diagram A

E1 F1

F2

E2

E3

F3

F4

Elements to be found in EPC diagram B

XOR

E4, E5, E6 – events where splitting takes place

E4

E5

C

E6

F5

Hypothetical end process interface for EPC diagram A

E7

Hypothetical end process C interface for EPC diagram B

Elements to be found in EPC diagram C

Fig. 6. Flat EPC diagram illustrating principle 22 EPC A

EPC B

E1

F1

F2

EPC C

E2

E3

A_1

A_2

B

F3

F4

E4

E5

E6

XOR

E4

E5

E6

F5

C_1

C_2

C_3

E7

Fig. 7. EPC diagrams developed based on the diagram provided in figure 6

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23. When there is a proper event among the preceding events for hypothetical end process interfaces, one that has been introduced by functions ultimately to be found indifferent EPC diagrams, then such an event should be divided into two partial events – a situation illustrated in figures 8, 9 and 10.

24. When there is a shared event among the preceding events for hypothetical end process interfaces, one must add an apparent function between the event and the process interface – a situation illustrated in figures 11, 12 and 13. Elements to be found in EPC diagram A

F1

Elements to be found in EPC diagram D Elements to be found in EPC diagram A

E1 F1

F2

E2

E3

F3

F4

E4

E5

C F5

Hypothetical end process interface for EPC diagram A

E7

Elements to be found in EPC diagram B

Elements to be found in EPC diagram C

F1 E4, E5, E6_1, E6_2 – events where splitting takes place

E2 F3

F4

E6_1

E6_2

F2

E4

E5

XOR

C

F5

Hypothetical end process interface for EPC diagram A

Elements to be found in EPC diagram B

E3

E7

E3

E4

Elements to be found in EPC diagram C

E1 F1

Elements to be found in EPC diagram D E1

F3

Elements to be found in EPC diagram A

Fig. 8. Flat EPC diagram in need of modification, illustrating principle 23

Elements to be found in EPC diagram A

F2

Fig. 11. Flat EPC diagram in need of modification, illustrating principle 24

Hypothetical end process interface for EPC diagram D

C

B

E2

C

Hypothetical end process interface for EPC diagram B

E6

C

E2 – events where splitting takes place

Elements to be found in EPC diagram B

XOR

E4, E5, E6 – events where splitting takes place

Hypothetical end process interface for EPC diagram A

E1

Hypothetical end process interface for EPC diagram C B Hypothetical end process C interface for EPC diagram Elements D to be found in EPC diagram C

E2

FX – apparent function e.g. “Send START signal for B” FY – apparent function e.g. “Send START signal for C”

FX

FY

EX

EY

FX, FY – apparent events where splitting takes place

F2

F3

Elements to be found in EPC diagram B

E3

E4

Hypothetical end process interface for EPC diagram A

C B Elements to be found in EPC diagram C

Fig. 12. Modified diagram from figure 8 EPC A E1

EPC B EPC C A_1

A_2

EX

EY

F2

F3

E3

E4

F1 E2

Fig. 9. Modified diagram from figure 8 EPC A

EPC B EPC D

E1

E2

E3

F2

F3

F4

E4

E5

E6_1

E6_2

C_1

C_2

C_3

C_4

F1

EPC C A_1

A_2

E4

E5

B

D

E6_1 E6_2

FY

EX

EY

B

C

Fig. 13. Linked EPC diagrams developed based on the diagram provided in figures 11 and 12

F5

Conclusions

E7

The main advantages of the EPC diagram linking concept proposed are its simplicity and trans-

Fig. 10. Linked EPC diagrams developed based on the diagram provided in figures 8 and 9 Zeszyty Naukowe 34(106)

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parency. Linking every process interface with exactly one event enables avoiding situations when events occurring in different diagrams can be linked with different elements. The process of developing a single EPC diagram based on several linked ones consists in disregarding all process interfaces and merging appropriate events. The main inconvenience related to the linking methodology discussed is the necessity to modify diagrams to be linked in specific cases. However, bearing the aforementioned advantages in mind, such an inconvenience should be considered acceptable.

8.

9.

10. 11.

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