Jörg Nitzsche

Semantic Service Bus: Architecture and Implementation of a Next Generation Middleware

In this paper we present a middleware for the service oriented architecture, called the Semantic Service Bus. It is an advanced middleware possessing enhanced features, as compared to the conventional service buses. It is distinguished by the fact that it uses semantic description of service capabilities, and requirements towards services to enable more elaborate service discovery, selection, routing, composition and data mediation. The contributions of the paper are the conceptual architecture of the Semantic Service Bus and a prototypical implementation supporting different semantic Web service technologies (OWL-S and WSMO) and conventional Web services. Since mission critical application scenarios (for SOA) involve complex orchestrations of services, we have chosen to utilize semantically annotated service orchestrations as the applications to employ this middleware.

BPEL for semantic web services (BPEL4SWS)

In this paper we present BPEL for Semantic Web Services (BPEL4SWS) - a language that facilitates the orchestration of Semantic Web Services using a process based approach. It is based on the idea of WSDL-less BPEL and enables describing activity implementations semantically which increases the flexibility of business processes. Following an approach that uses a set of composable standards and specifications, BPEL4SWS is independent of any Semantic Web Service framework. It can be used to compose Semantic Web Services, traditional Web Services and a mix of them.

Parameterized BPEL processes: concepts and implementation

This paper presents the concept of parameterized WS-flows and two extensions to the BPEL language for enabling it. Another major contribution is a prototypical infrastructure enacting the execution, monitoring and adaptation of parameterized BPEL processes. The advantages of parameterized BPEL processes are the improved flexibility and reusability.

On Visualizing and Modelling BPEL with BPMN

The advantages of the process-based approach toimplementing applications lead to the development ofnotations for modelling business processes andlanguages for enacting them in a process engine forthe purpose of process automation. Currently theBusiness Process Modeling Notation (BPMN) istypically used for modelling business processes andthe Business Process Execution Language (BPEL) isused as the process execution format. Both languagesdiffer in purpose, expressivity and operationalsemantics. Recently it has been shown that there is nocomplete bi-directional mapping between BPMN andBPEL and transformations have been defined betweenthe two formalisms. However, these transformationslead to more complex models in both, BPEL andBPMN, and enable a roundtrip for only a limitednumber of scenarios. In this paper we show how BPELprocesses can be modelled using the graphical aspectof BPMN in order to facilitate modelling of executableprocesses using BPMN while avoiding modeltransformations.

Towards a Methodology for Semantic Business Process Modeling and Configuration

This paper discusses potential benefits from adding semantics to Business Process Management from a methodological point of view, with a focus on the Modeling and Configuration phases. For this purpose, in each of these phases the established activities are examined and new activities are suggested: Firstly, we suggest combining existing control flow validation techniques with semantic process validation techniques. Second, discovery and composition techniques can be used to find implementations, e.g. services (or combinations of services), for the implementation of process activities at modeling time. The discovered implementations allow for mapping the process steps to the IT infrastructure according to several strategies during process configuration, which helps clearly separating modeling from configuration concerns. Furthermore, a new way of testing executable process models is suggested.

A Management Framework for WS-BPEL

WS-BPEL is the standard to define executable business processes in a Web service world. Numerous commercial and open source BPEL engines exist on the market today that allow the execution of process models defined in BPEL. However, these execution engines only provide access to process model and process instance data in terms of proprietary APIs. In this paper we present an approach that models BPEL process models and process instances as resources and thus provides a uniform access scheme for process model and process instance data. This is crucial because access to process model and process instance data is needed in different scenarios that are of key relevance in enterprises today. These scenarios include compliance checking, repair of faulted business processes as well as real-time monitoring of business processes. The lack of a uniform access scheme to process model and process instance data hampers the exchangeability of BPEL engines and therefore results in a potential vendor lock-in.

WSDL 2.0 Message Exchange Patterns: Limitations and Opportunities

The Web Service Description Language (WSDL) provides means to describe functional aspects of a service in a service oriented architecture (SOA) based on Web service technology. In contrast to its predecessor (WSDL 1.1), WSDL 2.0 does not define a fixed set of operation types but provides for a generic mechanism to define an operation by means of message exchange patterns (MEPs). In this paper we compare the expressivity of MEPs in general with other work and formalisms in the field of service interaction. Furthermore, we identify new MEPs and extend the template used to define MEPs to allow expressing more complex patterns. We give a refined definition of MEPs based on a detailed discussion and discuss how WSDL and the MEPs in particular can be combined with the choreography approach.

An Execution Engine for Semantic Business Processes

In this paper we present the architecture and design of an extended BPEL engine that implements the operational semantics of BPEL4SWS. BPEL4SWS is an extension of the BPEL language with support for Semantic Web Service concepts like mediation and semantic descriptions of activity implementations. We describe the basic communication scenarios of processes with services and the interaction between the engine components involved in the execution of BPEL4SWS processes. The presented prototype is based on the open source BPEL engine Apache ODE, features improved configurability and facilitates the definition of additional BPEL extensions with minimal development effort.

Conversational Web Services: leveraging BPELlight for expressing WSDL 2.0 message exchange patterns

Message exchange patterns provide means to define the message flow of a service and how these messages are related in an abstract and reusable manner. They are an integral part of WSDL 2.0 and allow defining operations that have a message exchange beyond request-response. They reduce the impedance mismatch between imperative programming and message orientation while emphasising the message orientated nature of Web Services. Whereas BPEL defines a flow between Web Service operations, BPELlight is an appropriate candidate to define the flow within operations since it abstracts from WSDL. In this article we use BPELlight to capture complex message exchanges. We show how its partner model can be used to not only define bilateral message exchanges but also those conversations that involve different partner types and/or multiple instances of such partners. Therefore we introduce first-class mechanisms to store, query and thus distinguish addressing information related to multiple partner instances. In addition, we increase reusability by allowing recursive definitions of such models. Thus, we enable modelling message exchange patterns that capture business logic in a reusable manner on an abstract level like for instance a request for bid scenario or a business transaction for purchase. Finally, we show how such patterns can be generically mapped to transport protocols.

Formalising Message Exchange Patterns using BPEL Light

In a message-driven SOA, message exchange patterns (MEPs) define a reusable notion of conversational contracts between a service consumer and a service provider from the providers point of view. They enable a common understanding regarding a message flow between both parties. In contrast to version 1.1 of the Web Service Description Language (WSDL) the current version 2.0 has introduced a template for defining such patterns that allows to define and reference patterns beyond the standard input/output ones defined in the specification. Although reasonable, this approach brings several disadvantages which we point out in this paper. Since WSDL 2.0 MEPs and WS-BPEL processes describe interaction behaviour from the same perspective BPEL makes a perfect candidate as a language for formalising MEPs, especially because it provides a powerful mechanism for describing control flow and correlation of related messages. In this work we propose a way to formalising MEPs using a WSDL-less BPEL dialect called BPEL light. We introduce a new abstract BPEL profile for defining reusable and machine-readable MEPs that is capable of expressing arbitrary message exchanges. With this approach we pave the way for more flexible interaction styles and reduce the impedance mismatch between imperative programming and message orientation.