Yushun Fan

A Petri Net-Based Method for Compatibility Analysis and Composition of Web Services in Business Process Execution Language

Automatic Web service composition is gaining momentum as the potential silver bullet in service oriented architecture. The need for interservice compatibility analysis and indirect composition has gone beyond what the existing service composition/verification technologies can handle. Given two services whose interface invocation constraints are described by a Web services-business process execution language (WS-BPEL or BPEL), we analyze their compatibility and adopt mediation as a lightweight approach to make them compatible without changing their internal logic. We first transform a BPEL description into a service workflow net, which is a kind of colored Petri net (CPN). Based on this formalism, we analyze the compatibility of two services, and then devise an approach to check whether there exists any message mediator so that their composition does not violate the constraints imposed by either side. The method for mediator generation is finally proposed to assist the automatic composition of partially compatible services. Our approach is validated through a real-life case and further research directions are pointed out.

Performance modeling and analysis of workflow

Workflow model analysis is performed at logic, temporal, and performance levels. This paper mainly deals with the performance level issues. Workflow net (WF-net) is extended with time information to the timing workflow net (TWF-net). To provide a formal framework for modeling and analyzing workflow, this paper proposes a multidimension workflow net (MWF-net) that include multiple TWF-nets and the organization and resource information. The algorithm to decompose a free-choice and acyclic Petri nets (PN) into a set of T-components is extended to a TWF-net containing iteration structures. Then, resource availability and workload analysis is performed. A method for computing the lower bound of average turnaround time of transaction instances processed in a MWF-net is proposed. Finally a case study is used to show that the proposed method can be effectively utilized in practice.

A Petri Net Approach to Analysis and Composition of Web Services

Business process execution language for Web services (BPEL) is becoming the industrial standard for modeling Web-service-based business processes. Behavioral compatibility for Web service composition is one of the most important topics. The commonly used reachability exploration method focuses on verifying deadlock freeness. When this property is violated, the states and traces in the reachability graph only give clues to redesign the composition. The redesign must then repeat itself until no deadlock is found. In this paper, multiple Web service interaction is modeled with a Petri net called composition net (C-net for short). The problem of behavioral compatibility among Web services is hence transformed into the deadlock structure problem of a C-net. If services are incompatible, a policy based on appending additional information channels is proposed. It is proved that the policy can offer a good solution that can be mapped back into the BPEL models automatically.

Timing constraint workflow nets for workflow analysis

The analysis of the correctness and rationality of a workflow model plays an important role in the research of workflow techniques and successful implementation of workflow management. This paper points out the relevant problems in the verification and analysis of a workflow model. It discusses two important properties: schedulability and boundedness of a workflow model considering timing constraints. To specify the timing constraints, WorkFlow net is extended with time information, leading to timing constraint workflow net (TCWF-net). This paper presents a model mapping method to convert a directed network graph (DNG) based workflow model, which is built by a graphic process modeling language extended with time information, into a TCWF-net. It then discusses its schedulability verification and synthesis. An algorithm to decompose an acyclic and free-choice TCWF-net into a set of T-components is presented, followed by a boundedness verification method. The usefulness of the research results is illustrated by an example.

QoS-Aware Web Service Configuration

With the development of enterprise-wide and cross-enterprise application integration and interoperation toward Web service, Web service providers try to not only fulfill the functional requirements of Web service users but also satisfy their nonfunctional conditions in order to survive in the competitive market. A hot research topic is how to configure Web services to meet their demand when the diversity of user requirements, distinction of service components performance, and limitation of resources are considered. This paper builds a Web service configuration net based on Petri nets in order to exhibit Web service configurations in a formal way. Then, an optimal algorithm is presented to help choose the best configuration with the highest quality of service to meet users nonfunctional requirements. Finally, the simulation results and related analysis prove the soundness and correctness of our model and algorithm.

Data-Driven Service Composition in Enterprise SOA Solutions: A Petri Net Approach

Under Service Oriented Architecture (SOA), service composition is used to integrate service components together to meet new business needs. In this paper, we propose a novel data-driven method to provide service composition guidance to implement given requirements. Based on the relations between business domain data and service domain data, we generate additional data mediations according to three composition rules. With these data relations and composition rules, we propose a Petri-net based approach to the composition of services. In our approach, all the in/output messages of the service operations are modeled as colored places, and service operations themselves are modeled as transitions with input/output places. We first generate a Service Net (SN) that contains all operations in a given service portfolio, and then use Petri-net decomposition techniques to derive a subnet of SN, and this subnet meets the need of the business requirement. Our work can be seen as an effort to bridge the gap between business and service domains.

Web Service Configuration Under Multiple Quality-of-Service Attributes

With the popularity of Internet technology, Web services are becoming the most promising paradigm for distributed computing. However, when a single Web service fails to meet service requestors multiple function needs, web services need to be dynamically configured together to form a web service composition. Since there may be many configurations providing identical functionality with different quality-of-service (QoS), a choice needs to be made according to users functional and nonfunctional requirements. In this paper, we formulate a Web service functional configuration problem by using Petri nets. The graph structure and algebraic properties of the model are analyzed in detail to show that a basis solution of a state-shift equation of the Petri net model corresponds to a realizable configuration process. This result is later used to formulate the multiple attribute QoS optimization problem to a linear programming problem. Finally, a case study is performed to show that the proposed analysis result can be effectively applied in practice.

A Petri Net Approach to Analyzing Behavioral Compatibility and Similarity of Web Services

Web services have become the technology of choice for service-oriented computing implementation, where Web services can be composed in response to some users needs. It is critical to verify the compatibility of component Web services to ensure the correctness of the whole composition in which these components participate. Traditionally, two conditions need to be satisfied during the verification of compatibility: reachable termination and proper termination. Unfortunately, it is complex and time consuming to verify those two conditions. To reduce the complexity of this verification, we model Web services using colored Petri nets (PNs) so that a specific property of their structures is looked into, namely, well structuredness. We prove that only reachable termination needs to be satisfied when verifying behavioral compatibility among well-structured Web services. When a composition is declared as valid and in the case where one of its component Web services fails at run time, an alternative one with similar behavior needs to come into play as a substitute. Thus, it is important to develop effective approaches that permit one to analyze the similarity of Web services. Although many existing approaches utilize PNs to analyze behavioral compatibility, few of them explore further appropriate definitions of behavioral similarity and provide a user-friendly tool with automatic verification. In this paper, we introduce a formal definition of context-independent similarity and show that a Web service can be substituted by an alternative peer of similar behavior without intervening other Web services in the composition. Therefore, the cost of verifying service substitutability is largely reduced. We also provide an algorithm for the verification and implement it in a tool. Using the tool, the verification of behavioral similarity of Web services can be performed in an automatic way.

Optimal service selection and composition for service-oriented manufacturing network

The management of services is the kernel content of service-oriented manufacturing. However, it is difficult to realise the integration and optimisation of services in an open environment, which contains large amounts randomicity and uncertainty. The key problem is how to realise the optimal service selection and composition. In this article, the comprehensive performance evaluation metrics for service-oriented manufacturing network is proposed, which combines the key performance indicators of services in business, service and implementation level. The performance evaluation model is brought forward to analyse the local and global performance. An uncertainty and genetic algorithm-based method is developed to realise the optimal service selection and composition in effective and efficient way.

Dynamic Checking and Solution to Temporal Violations in Concurrent Workflow Processes

Current methods that deal with concurrent workflow temporal violations only focus on checking whether there are any temporal violations. They are not able to point out the path where the temporal violation happens and thus cannot provide specific solutions. This paper presents an approach based on a sprouting graph to find out the temporal violation paths in concurrent workflow processes as well as possible solutions to resolve the temporal violations. First, we model concurrent workflow processes with time workflow net and a sprouting graph. Second, we update the sprouting graph at the checking point. Finally, we find out the temporal violation paths and provide solutions. We apply the approach in a real business scenario to illustrate its advantages: 1) It can dynamically check temporal constraints of multiple concurrent workflow processes with resource constraints; 2) it can give the path information in the workflow processes where the temporal violation happens; and 3) it can provide solution to the temporal violation based on the analysis.