Grupo:: Research Group:

• TICSw-Tecnologías de Información y Construcción de Software

Intereses y líneas de Investigación:

• Model Driven Engineering
• Enterprise Architectures
• Executable Models
• Domain Specific Languages
• Business Process Management
• Software Architecture

PhD Thesis: Executable Models for Extensible Workflow Engines

Promoters:

• Jorge Villalobos (Universidad de los Andes)
• Viviane Jonckers (Vrije Universiteit Brussel)
• Dirk Deridder (Vrije Universiteit Brussel).

Keywords

Executable Models, Model Driven Engineering, Workflow Engines, Workflow Specification Languages, Concern Specific Workflow Languages.

Abstract

In recent years, workflows have started to be used in many domains such as business processes, scientific applications, and e-learning. Accordingly, various workflow specification languages have needed to be designed in each one of those domains. Corresponding infrastructures (like editors, engines, and monitoring applications) to utilize and enact those languages have been implemented as well. Among the benefits commonly associated with workflows, one that stands out is the possibility of modifying workflow definitions by manipulating only high level or domain specific concepts. This is extremely positive because it enables domain experts to introduce changes to the systems without requiring the intervention of software developers. However, this flexibility is not always enough. Workflow users often encounter new requirements that cannot be properly solved with existing tools and languages because they depend on new concepts or should use different structures. In those cases, their only options are to change or extend the workflow languages, or to develop entire new ones. Unfortunately, nowadays there is poor support to implement either alternative. With the former, the biggest problem is that workflow languages and their associated tools have very limited extensibility capabilities. With the latter, there are two different problems. The first one is the scarcity of frameworks or libraries available to support the development of new workflow engines to enact the newly created languages. The second problem is that existing engines are tightly coupled to the languages they were developed for. Therefore, by creating a new language one looses existing tool support (editors, simulators, monitoring applications, and others).

The goal of this dissertation is to solve these limitations by offering a platform that serves as the foundation for extensible workflow engines. In this way, the enactment of new workflow languages will be more easily supported, because the implementation of every engine will not start from scratch. Furthermore, this platform is geared towards supporting extensible and flexible workflow languages, and thus changing requirements will be more easily accommodated. The proposed platform supports various kinds of workflow languages. In the first place, there are general purpose workflow languages that can be used in many domains, such as BPEL or BPMN. Another kind is that of domain specific workflow languages, such as IMS-LD or Sedna. Finally, the proposed platform also supports concern specific workflow languages, which modularize workflow descriptions in accordance with various possible criteria.

There are three ideas that are central to the proposal. First of all, there is the idea of using metamodels to define the structure of workflow languages, and using models to represent specific workflows. The second idea is that of making the models executable by establishing executable semantics for every element in the metamodels, and following the semantics of the language. Finally, the third idea is that of coordinating the execution of several executable models in order to support the aforementioned concern specific languages. To support these three ideas we developed the notion of `open objects’, which are used to define the behavior of elements of the metamodels in a special way. By using open objects, each element defines its own semantics. However, the actual coordination between those elements is specified in an explicit and flexible way. It is the responsibility of a special kernel in the platform to use this information to coordinate the behavior of the elements and thus execute the workflows. Furthermore, this kernel also provides other features common to workflow systems. Therefore, these features do not have to be reimplemented for every language.

The ideas presented in this dissertation have been implemented in the Cumbia platform, which encompasses a Java based development framework, and two components called Cumbia Kernel and Cumbia Weaver. Concretely, the framework is what workflow language developers need to build their own metamodels based on open objects. The Cumbia Kernel is the component that loads and runs the models. The Cumbia Weaver is what establishes relationships between models conformant to different metamodels, thus allowing the interaction of concern specific languages.

This approach has been validated with the construction of engines for well known workflow languages, which include BPEL, BPMN and YAWL. Other experiments include the implementation of engines for concern specific workflow languages (miniBPMN, XPM, and XTM), and for domain specific workflow languages (IMS-LD and PaperXpress).

File

Dissertation: Download.pdf