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A Survey on the Transformation of Business Proccess Modelling Language to Business Process Execution Language Essays

A Survey on The Transformation of Business Proccess Modelling Language to Business Process Execution Language Muhammad Rifqi Ma’arif Dept. of Industrial & Systems Engineering Dongguk University – Seoul [email protected]. com Abstract. In Business Process Management (BPM), business processes are often modeled in a explicit way by using Business Process Modeling Language (BPML). BPML was reprsented with a graphical form, which make a better interpretation of business process within the organization. But in another hand, the business process itself need to execute by some execution engine.
Since the execution engine can not deal with the graphical structure, The BPML need to transform into executable language. One of the most popular executable language for business process is Business Process Execution Language (BPEL). This paper aims to summarize the work which perform a transformation from several graphical business process modeling language into BPEL. Keyword : Business Process Execution Language (BPEL), Business Process Modeling Notation (BPMN), UML Activity Diagram, Event-driven Process Chain (EPC), Petri Nets, Transformations. . Introduction Business process execution was addressed to the automation or implementation of designed business process in executable enviroment. To perform this task there was exsist several execution language. One of the most popular among them is Business Process Execution Language (BPEL) which widely used in the current industry. BPEL was standardized by Organization for the Advancement of Structured Information Standards (OASIS) as standard executable language for specifying actions within business process with web services (Alvet et. l, 2007). Before going further to the executable platform or enviroment, business process itself usually modelled using business process modeling language like BPMN, UML Activity Diagram, Petri Nets, etc. There is some advantages of modeling the business process in a such way. First the business process is easier to understand. Second is a possibility to have rich representation of business process since business environments have a many stakeholders which different perspective and interest to the business.
But there is a gap exist between business process modeling language with the execution language, since they have different structure and interpretation. The BPEL is a mainly block-structured language supported by several execution platforms. In the other hand most of the business process modeling language is a graphoriented language in which control and action nodes can beconnected almost arbitrarily. In this paper, we will cover a number of transformations from business models in BPMN, UML 2. 0 Activity 1 Final project in Business Process Management class – Dongguk University, Fall 2011
Diagram, Event-driven Process Chain (EPC) and Petri Nets, focusing on transformations onto BPEL. We make some classification based on the modeling language to be tranformed onto BPEL and elaborate the kind of approach proposed to solve the transformation problems. The structure of this paper is arranged as follows, section two will give a briefly introduction about Business Process Execution Language (BPEL). Chapter 3 is the body of this paper which dicuss about the transformation approach for each diagram, and finaly chapter 4 outlined the conclusion and future works. 2.
The Business Process Execution Language (BPEL) Business Process Execution Language for Web Service (BPEL4WS) or BPEL (IBM, 2003) is a XML-based language used to define enterprise business processes within Web services. BPEL supports the specification of serviceoriented processes, that is, processes in which each elementary step is either an internal action performed by a Web service or a communication action performed by a Web service (sending and/or receiving a message). They can be executed to implement a new Web service as a concrete aggregation of existing services to deliver its functionality (i. . composite Web service) (Ouyang, 2007) 2. 1 The History of BPEL Since 2000 there has been a growing interest in Web services. This resulted in a stack of Internet standards (HTTP, XML, SOAP, WSDL, and UDDI) which needed to be complemented by a process layer. Several vendors proposed competing languages, for example,, IBM proposed WSFL (Web Services Flow Language) (Leymann, 2001) building on FlowMark/MQ-Series and Microsoft proposed XLANG (Web Services for Business Process Design) (Thatte, 2001) building on Biztalk.
BPEL arised as the convergence of those language features, which is the orchestration language, used in BizTalk server and has a block-structured approach. Both WSFL and XLANG are now was substituted by the BPEL specification. BPEL 1. 0 was jointly developed by IBM, BEA, SAP, Siebel, and Microsoft in August 2002. In April 2003, BPEL 1. 1 was submitted to OASIS to obtain even broader industry acceptance and open standardization. (OASIS Web Services Business Process Execution Language TC, 2006). Currently BPEL is implemented in a variety of tools which support the execution BPEL (e. g WebSphere, Biztalk, etc). . 2 The BPEL Structure Each BPEL processes contains of three different parts. The BPEL code which defines the orchestration flow, WSDL interface which defines the interfaces and related XML schema of the BPEL process for its clients and one more WSDL interface of the consumed services (partner links). The overall structure of BPEL was depicted on figure 1. A BPEL process is composed of activities that can be combined through structured operators and related through so-called control links. In addition to the main process flow, BPEL provides event handling, fault handling and compensation (i. . , “undo”) capabilities. In the long running business processes, BPEL applies correlation mechanism to route messages to the correct process instance. Final project in Business Process Management class – Dongguk University, Fall 2011 2 Figure 1. Overal Structure of BPEL (Juric, 2009) 3. The Transformation In this section, four business process model thats are Business Process Modeling Language (BPMN), UML Activity Diagram (AD), Event-driven Process Chain (EPC) and Petri Nets were intoduced followed by the outlines of transformation approaches that have been done for each modeling languages. . 1 Business Process Modeling Language (BPMN) The BPMN (OMG, 2006) was introduced by the Business Process Management Initiative (BPMI. org) and has been standardized by the Object Management Group (OMG) as a standard for busines s process modeling. BPMN was used to modeling business process in conceptual level since it have a large collection of object types to represent various aspects of a business process, including the control? ow, data, resources and exceptions. The three types of BPMN objects that can be used to represent the control? w aspect of a process are activities, events, gateways. Many subtypes of these objects exist. Control-? ow objects can be connected by sequence ? ows, which are directed arcs that represent the ? ow of control from one object to the next. Actualy the translation mechanism from BPMN into BPEL wase described on the BPMN specification by OMG (OMG, 2006) which map the BPMN diagrams onto the BPEL blocks based on the structural similarities. This translation mechanism was addresed from the previous work which informaly sketched a translation of BPMN to BPEL (White, 2005).
The OMG’s mechanism also refined this transformation mechanism which employ some inefficiencies processed likes restriction to the BPMN diagrams and a user involvement during the transformation. In common with informal translation within OMG specification, BPMN was conducted to visualize the BPEL (Schum et. al, 2009). This work attempt to use the BPEL metamodels as the basis of process definition performed by BPMN. Thus, the BPEL code can directly generated from BPMN diagrams. Instead of informaly mapped the diagrams, a three different and incremental 3
Final project in Business Process Management class – Dongguk University, Fall 2011 work based on formalization techniques was conducted by Ouyang et. al (Ouyang, 2006) (Ouyang, 2008) (Ouyang, 2009). Generaly in their works they breaked down the transformation into two different steps, element preservation and element mapping. The element preservation phase was conducted to provide the formal definition of each BPMN diagrams before mapped with particular mapping techniques. On the first work (Ouyang, 2006) the Standard Process Model (SPM) was used as the core of diagram preservation.
SPM is a restricted business process model which constructed from a set of process elements and transitions that connecting them, and also known as Standard Workflow Model (SWM) (Kiepuzawski et. al, 2000). In this case the SPM framework was used to capture the control-flow perspective of BPMN, than this control-flow perspective was translate to defined pre-condition set and finaly the preserved contol flow mapped to the BPEL blocks with formal template called Event-Condition-Action (ECA) rules.
Since the formalism just occurred on the control-flow prespective this work was not covered all of the perspective of BPMN diagram. The second work (Ouyang, 2008) was performed to refine this condition. In this work, different approach was implented either on the element preservation and element mappig. Since the BPEL was represent by blockstructure, the element preservation phase on this work was attempted to transform the graph-structure of BPMN to the blockstructure first.
To do this kind of work, the BPMN diagrams was decomposed into three differents block : well-structured that conforms to BPEL structured activities, generalized flow pattern that can be mapped onto BPEL contol links and quasi-structured fragments that can be turned into perfectly structured ones and ? ow-based acyclic fragments that can be mapped into a combination of block-structured constructs and control links. The third work (Ouyang, 2009) actualy is a combination of the fisrt and second work.
This work was conducted to identify the core subset of BPMN which contains paralelism and map directly onto BPEL code. The control subset was identified by defining abstract syntax and semantics of BPMN by using petri nets, since BPMN specification have no defined semantic. But this work is not enough, because the generated BPEL code is not readably. To overcome this problems, two classes of BPMN model have been identified. First class was correspond to the Structured Process Model (SPM) to capture the control-flow perspective and translate them to the five structured control-flow in BPEL.
The seccond class was correspond to the synchronization process model which captured by the quasi-structured pattern and translated them to the BPEL control link. Another approach to transforming the BPMN diagrams to the BPEL code was conducted by adopting the mature methodology from software engineering area called model transformation (Czanerski and Helson, 2006). The most important things must be considered regarding the adaptation of model transformation approach to transforming business process model is a metamodel definition.
Since BPMN specification has no defined metamodel, and so far two different ways have been performed. The first way is defining the BPMN metamodel arbitrarily (Bierman, 2009), while the second way is conforming BPMN to the metamodel of particular modeling tool which has an ability to generate the BPEL code (Giner, 2007) Final project in Business Process Management class – Dongguk University, Fall 2011 4 3. 2 UML Activity Diagram (AD) Activity diagrams are graphical representations of workflows of stepwise activities and actions with support for choice, iteration and concurrency.
In the, Unified Modeling Language (UML), activity diagrams can be used to describe the business and operational step-by-step workflows of components in a system. An activity diagram shows the overall flow of control. The main concepts of the AD are actions and swimlanes, whereby the latter represent roles (List and Korher, 2006) UML diagrams have a one particular features which provides a generic extension mechanism for customizing UML models for particular domains and platforms called UML Profile (Alhir, 2002).
Since extension mechanisms allow refining standard semantics in strictly additive manner they can’t contradict with standard semantics, thus the AD to BPEL transformation problems can be solved by using this feature. The transformation which based on the definition of UML profile can be practicaly implemented in several purposes likes emerging the possibility of modelling BPEL with activity diagram and bind it to the model driven development framework to generate BPEL code (Gardner & Tracy, 2003) (Skogan et. al, 2004), or mapping activity diagram directly to the BPEL (Korher et. l, 2006). As well as the BPMN to BPEL transformation which adopted the model transformation approach, a similar techniques also implemented to the activity diagram (Lohman et. al, 2007). By using graph-based model transformation which employ triple-graph grammar concept to transforming a particular model to another the BPEL and XPDL code were generalized from defined activity diagrams. Triplegraph grammars allowed structural relationship between the different model elements to be elegantly expressed in graphical and declarative rules.
The similar adoption of graph-based model transformation also performed to create a heuristic transformation algorithm (Hauser, 2004) which consentrate on the transformation of the control-flow pattern within the process model to the BPEL activities. 3. 3 Event-driven Process Chain (EPC) The EPC (Scherer, 1999) has been developed for modelling business processes with the goal to be easily understood and used by business people. The basic elements of EPC are functions and events. Functions model the activities of a business process, while events are created by processing functions or by actors outside of the model.
Since EPC have the most similar abstract concept with BPEL comparing to the another business process modeling language, there was an attempts to conceptually mapping the EPC diagram onto BPEL code (Zieman, 2006). This conceptual mapping is based on the several defined assumptions, the mapping result is consider to be accurate if these assumptions were satisfied. One of the assumption that have the highest influence was assumed that BPEL basic activities are modeled as function-event blocks in EPC diagram. A BPEL activity was identified by the text label of EPC function.
From this assumption, a direct and informal mapping from EPC function to the BPEL basic activity was conducted. More formal approach to visualizing BPEL as EPC model (Mendling, 2006) was conducted by de? ning process graphs as an abstraction of EPC diagram and BPEL control ? ow as an abstraction of BPEL. Then the Flattening, Hierarchy5 Final project in Business Process Management class – Dongguk University, Fall 2011 Preservation, and the HierarchyMaximization strategy for transformations from BPEL control ? ow to process graphs were identified respectively. In the other direction Element-Preservation, ElementMinimization, Structure-Identi? ation, and Structure-Maximization strategy were also defined. These four processes were performed to clearly defined the possible optimal structure to visualizing BPEL as EPC model. 3. 4 Petri Net A Petri Net (Murata, 1988) is designed for modelling, analysis and simulation of dynamic systems with concurrent and nondeterministic procedures. Petri Nets are utilised for modelling workflows. A Petri Net is a directed graph that mainly consists of two different nodes, places and transitions. Places represent possible states of the system. Transitions are events or actions which cause the change of state.
The work for transforming the petri net or workflow net model into BPEL is dominated by formal mechanism. Different formalization techniques have been performed to this purpose. For example using decomposition mechanism (Aalst, 2003) to breaked down the workflow net (a special case of petri nets) into component. A component should be seen as a selected part of workflow net that have clear start and end which used to bridge the different type of language structure, workflow net which representation of graph-structure language and BPEL which representation of blockstructure language.
Different formalization mechanisms employ another special class of petri net called open workflow net (oWFN) which generalize clasical workflow net by introducing an interface for asynchronus message passing. This special type of petri nets provide a simple but formal foundation to model service and their interaction which close to abstract concept of BPEL. This proximity is make posible to map the oWFN model into the abstract BPEL just by adding some anotation into the oWFN ‘s element. And with some light adjustment and refinement the abstract BPEL can be modified into executable BPEL code. . Conclusion and Future Work There were a various possible way to transform the business process model to the execution language with its advantages and waekness. The reviewed papers regarding to this survey showed three general approach and one special approach that can be done to solve the transformation problems. The three general approaches are formalization, informal mapping, and adoption of model transformation approach. And the special approach is employing a special feature of UML diagram called UML profile. This approach is suitable only with UML activity diagram.
Formalization usulay consist of multiple steps with a strict mechanisms in element preservation. This method may have many adavantages regarding to its formal structure like easy to validate and trace, provide a precise mapping, reasonable, etc. But this mechanisms is hard to implemet. The informal mapping is very practice way, just by sketching the similar structure or conforming a metamodels. But the informal way is lack for formalism so the mapping results may inconsistent. Adopting the model transformation approach is a good idea, since this approach has reach the level of maturity to tranform two or more models.
But the problem is the suitability of applying model transformation to process modeling is still debated, becaues its come from different area. Another way to 6 Final project in Business Process Management class – Dongguk University, Fall 2011 transform the business process model especialy activity diagram is using language feature such as UML profiler may ease the transformation process because its adding detail to the existing diagram. But it may time and effort consuming, because defining a comperhensive and robust UML profile is not always an easy work.
The future work of this topics can be conducted to overcome several waekness of the existing approach. A new formalism mechanism based on ontology engineering is may potential to develop. Since ontology has a formal structure its easier to understand and implements rather than performed formalism techniques on the previous works. The other potential works to do is assesing a suitability of model transformation approaches in the case of its implementation on this process modeling area. Refferences Alves , A. , et al. : Web Services Business Process Execution Language Version 2. 0.
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