BPEL Activities Research Articles

S2O: A smart objects orchestrator framework based on the web of things

The Web of Things (WoT) is a new paradigm in which everyday objects are connected to the Internet using popular Web technologies. The smart things are abstracted into RESTful Web services to facilitate their manipulation. The composition of these objects within the same business process creates an automated, time-synchronized routine that can perform even the most complex tasks. BPEL is an orchestration language that defines the process responsible for coordinating the Web services involved. However, this language presents some limitations in this context. BPEL 2.0 does not support RESTful Web services; its specification is incompatible with this architectural style of services. Moreover, its temporal expressivity is insufficient to cover all the constraints that may arise when composing services. This work aims to adapt BPEL to the requirements of the WoT environment, enabling it to create processes that invoke the smart things in precise time intervals. The solution is to exploit one of BPEL's strengths: its extensibility. The BPEL specification is enriched with four activities that reflect the REST uniform interface. They include the necessary attributes to send the request to the target object and receive the response in convened format representation. Also, temporal attributes are added to BPEL elements to schedule their start, end, and duration of execution. The manual addition of these temporal values requires a verification of their accuracy. The BPEL process must be reviewed to ensure its validity before its execution. A temporal Petri Net is proposed to detect any conflicts or inconsistencies between BPEL activities. As a result, associating the formal model with the extension allows BPEL to orchestrate smart things represented by RESTful Web services according to a well-defined temporal scenario. They respect the REST constraints and provide the BPEL activities with temporal attributes for efficient time management. The approach can be applied in all application areas to create temporal scenarios.

An algebraic theory for web service contracts

Abstract We study the foundations of Web service technologies for connecting abstract and concrete service definitions and for discovering services according to their observable behavior. We pursue this study addressing a subset of BPEL activities that include concurrency constructs. We present a formal semantics—called compliance preorder —of this subset of BPEL and we define a behavioral type discipline that guarantees the correctness of client-server interactions. The types of our discipline, called contracts , are De Nicola and Hennessy tau-less, finite-state CCS processes. We show that contracts are BPEL normal forms according to the compliance preorder and that the compliance preorder does coincide with a well-known equivalence in concurrency theory, the must-testing preorder . The compliace preorder is not fully adequate for discovering Web services though, since it does not support width and depth extensions of Web services. To address this issue, we propose a sound generalization of the compliance preorder, called subcontract relation , that admits a notion of principal service contract—the dual contract —compliant with a given client contract and that exhibits good precongruence properties when choreographies of Web services are considered.

An Empirical Analysis of Business Process Execution Language Usage

The current state of executable business process languages allows for and demands optimization of design practices and specifications. In this paper, we present the first empirical study that analyses Web Services Business Process Execution Language (WS-BPEL or BPEL) usage and characteristics of real world executable business processes. We have analysed 1,145 BPEL processes by measuring activity usage and process complexity. In addition, we investigated the occurrence of activity usage patterns. The results revealed that the usage frequency of BPEL activities varies and that some activities have a strong co-occurrence. BPEL activities often appear in activity patterns that are repeated in multiple processes. Furthermore, the current process complexity metrics have proved to be inadequate for measuring BPEL process complexity. The empirical results provide fundamental knowledge on how BPEL specification and process design practices can be improved. We propose BPEL design guidelines and BPEL language improvements for the design of more understandable and less complex processes. The results are of interest to business process language designers, business process tool developers, business process designers and developers, and software engineering researchers, and contribute to the general understanding of BPEL and service-oriented architecture.

Performance Evaluation of Web Services Orchestrated with WS-BPEL4 People

WS-BPEL Extension for People (BPEL4People) introduces human activity to Web Services Business Process Execution Language (WS-BPEL/BPEL). Some works have been done on the performance verification of WS-BPEL, but there aren't works on the performance verification of WS-BPEL4People. In this paper, we propose a model method for the transformation of WS-BPEL4People/BPEL4People into Generalized Stochastic Petri Nets (GSPN) and this way evaluate its performance. During the transformation, Petri Net is used to model BPEL activities and the human activity of a human task. Then, by validating the generated model, some potential problems with performance of WS-BPEL4People can be detected.

Engineering a BPEL orchestration engine as a multi-agent system

The BPEL language is currently the primary candidate for standardising Web Services orchestration. BPEL specifications are meant to be run by BPEL orchestration engines, which are therefore crucial components of today’s business-to-business infrastructures, carrying the burden of dynamically composing existing services. In this paper, we present the design of a BPEL orchestration engine based on a multi-agent system: while the basic BPEL activities are autonomously executed by agents, workflow aspects are realised by the mediation of ReSpecT tuple centres, a coordination model extending Linda with the ability of declaratively programming the tuple space behaviour. Our architecture separates the interaction, correlation, and workflow concerns into clearly identified tiers. In particular, we identify the workflow tier as the one encapsulating the core and most critical behaviour of the engine: due to its intrinsic complexity, we tackle its design formally. We introduce a core algebraic language of BPEL dealing with its workflow-related aspects, and provide it with a semantics based on a mapping into a net specification, modelling the dependencies between the activities to be executed by the engine. This mapping plays the role of a formal design, since it directly leads to an implementation of the workflow tier in the orchestration engine.