Cloud Transition: Integrating Cloud Calls into Workflow Petri Nets

Keywords

• Cloud computing
• Workflow Management Systems
• Workflow Petri Nets
• Reference Nets
• Cloud Workflow Transition

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In this paper, we present the Cloud Workflow Transition. An extension of Petri nets formalisms to adopt Cloud interactions. This allows workflows to request compute or storage services from the cloud. Such refinements permit to codify operational procedures into Petri net models and reduce user implication during the specification of their workflows. The main purpose behind our proposed refinements is to allow users to automatically execute workflows on distributed infrastructures (Cloud, SOA, grid, cluster).

Through the Cloud transition users can specify their requests formulated as tasks and parameters (see Figure 1). These requests will be treated in a transparent way i.e. that technical information is hidden from the user. The WFMS will then either accept the request and make the connection to the specified Cloud services according to user inputs or will reject it. The input places of the Cloud transition model the pre-conditions of an event, the input data for the computational task. The output places of the transition model the post-conditions associated with an event, the results of the computational task.

Our approach uses workflow Petri nets [ 1 ]. More specifically we use the reference net formalism [ 2 ] extended with a specialized workflow task transition [ 3 ]. Renew, the Reference Net Workshop, is our chosen tool for modeling with reference nets. A very interesting and useful property of reference nets in Renew is their use of the so-called shadow layer. It hides the technical details from the user, who can concentrate on simply the nets.

The technical integration of the Cloud transition into our workflow nets and workflow managment system is carried out in three main steps: The integration into the existing workflow net formalism for Renew [ 3 ], the integration into the current WFMS in Renew [ 4 ] and finally the integration into the user interface. Due to the dynamic aspect of the cloud computing, further integration issues are investigated such as including Quality-of-Service (QoS) requirements (time and expenditure limit). The WFMS should be able to identify and handle failures and support reliable execution in the presence of concurrency to guarantee a high level of performance and availability of services.

PNSE’12 – Petri Nets and Software Engineering

We plan to define the oprational semantics of the Cloud transition using Renew as well as a working use case. As an example, we intend to include the Cloud transition to model and enact a storage workflow using existing Cloud storage services within a Petri net-based multi-agent system.

References

1. Aalst , W.: Verification of workflow nets . In Azéma, P., Balbo , G., eds. : Application and Theory of Petri Nets 1997 . Volume 1248 of Lecture Notes in Computer Science., Springer-Verlag, Berlin ( 1997 ) 407 - 426

2. Kummer , O. : Referenznetze . Logos Verlag, Berlin ( 2002 )

3. Jacob , T. , Kummer , O. , Moldt , D. , Ultes-Nitsche , U. : Implementation of workflow systems using reference nets - security and operability aspects . In Jensen, K., ed. : Fourth Workshop and Tutorial on Practical Use of Coloured Petri Nets and the CPN Tools , Ny Munkegade, Bldg. 540, DK-8000 Aarhus C , Denmark, University of Aarhus, Department of Computer Science ( August 2002 ) DAIMI PB: Aarhus , Denmark, August 28 -30, number 560.

4. Wagner , T. : A centralized Petri net- and agent-based workflow management system . In Duvigneau, M. , Moldt , D., eds. : Proceedings of the Fifth International Workshop on Modeling of Objects, Components and Agents, MOCA'09 , Hamburg . Number FBI-HH-B-290/09 in Report of the Department of Informatics, Vogt-Kölln Str. 30 , D - 22527 Hamburg, University of Hamburg, Department of Informatics ( September 2009 ) 29 - 44