Roman Vaculín

Modeling and Discovery of Data Providing Services

Web Services providing access to datasources with structured data have an important place in the SOA. In this paper we focus on modeling and discovery of generic data providing services (DPS), with the goal of making data providing services available for interactions with service requesters in contexts such as service composition and mediation. In our model RDF Views are used to represent the content provided by the DPS. A characterization of match between description of DPS as RDF Views and the OWL-S service request is specified, based on which we developed a flexible matchmaking algorithm for discovery of data providing services. Finally, we propose a realization of the DPS using a SOAP version of the SPARQL protocol and a dynamic configuration interface allowing easy interactions of service requesters with data providing services.

Towards automatic mediation of OWL-S process models

The framework for automatic mediation of two process models composed of semantically annotated Web services is presented. Process mediation is hard because of many possible mismatches between process models. We introduce algorithms for the process models analysis to find possible mappings between providers and requesters process models, or to identify incompatibilities that cannot be reconciled with given set of available data mediators and external services. Results of the analysis phase are used in the mediator runtime component. In particular, we show how the workflow and dataflow mismatches can be resolved.

Exception Handling and Recovery of Semantic Web Services

In this paper we present an approach for specification of exception handling and recovery of semantic web services based on OWLS. We use standard fault handlers and compensation known for example from WS-BPEL to provide support for long running transactions. In addition to that, we introduce constraint violation handlers (CV-handlers) which allow a designer to define what situations are supposed to trigger an erroneous state and what are the appropriate recovery actions. Further, we introduce explicit recovery actions such as retry and replaceBy to recover from the failure and to restore a normal execution flow. By combining fault handlers, CV-handlers and standard event handlers it is possible to define ways of recovery for standard errors and for violations of constraints resulting for example from Service Level Agreements (SLAs).

Semantic Web Services Monitoring: An OWL-S Based Approach

In this paper we describe mechanisms for execution monitoring of semantic Web services, based on OWL-S. The use of semantic descriptions and ontologies is a valuable extension to current SOA conceptualizations. The described mechanisms are implemented as extensions of the OWL-S virtual machine that we have previously developed. The OWL-S virtual machine is a component that controls the interactions between a client and the Web service it uses. The presented extensions are a result of practical requirements that arose in the course of involvement with two projects that utilize OWL-S based semantic Web services. In particular, we present an event-based model for monitoring and logging interactions. The interaction trace allows a human or software agent to analyze, replay or debug the execution. Additionally, we describe proposed extensions to current specification in OWL-S for reporting and handling of errors. Finally, we describe extensions to the OWL-S virtual machine based on introspection to enable dynamic interactions with process mediators.

Specifying and Monitoring Composite Events for Semantic Web Services

Execution monitoring of complex web service process models is critical for effective management and control of web services based systems. During the composite process model execution or as part of the after-execution analysis complex event patterns (called composite events) consisting of various primitive events need to be detected. In this paper we introduce the concept of primitive semantic events that are used for monitoring of semantic web services, based on OWL-S. Next, we describe mechanisms for specification and detection of composite events. We present a language based on an event algebra combined with semantic event-filtering expressions using description logics atoms enriched with OWL datatypes and SWRL built-ins. Such a language can be used for specification of composite events allowing a detection of complex event patterns in the flow of primitive events. Furthermore, the semantic filtering allows detection of such events that would otherwise be impossible without the use of semantic descriptions. We also discuss detection mechanisms suitable for runtime execution and after-execution analysis.Service-Oriented Architectures (SOAs) are increasingly deployed to achieve distributed systems that are modular, flexible and extensible. Designing for a SOA can be difficult, however. There are issues involving the granularity of the cooperating services, and there are no currently accepted conventions for describing a service or its interactions at an abstract level. This paper presents the Service Responsibility and Interaction Design Method (SRI-DM), an agile approach for engineering a Web Service design, based on capturing a scenario as a use-case, factoring this into a set of Service Responsibility and Collaboration Cards, and constructing a Sequence diagram illustrating their interactions in fulfilling the scenario. The paper presents the notation for each step and describes with the aid of an example how this process is used to create a service design within the domain of e-assessment.

Recovery mechanisms for semantic web services

Web service-based applications are widely used, which has inevitably led to the need for proper mechanisms for the web service paradigm that can provide sustainable and reliable execution flows. In this paper we revise recovery techniques in OWL-S and show how semantic annotations may ensure seamless web service provision in a sophisticated way, such as, exploiting the ontology-based description of processes in order to dynamically find alternative services as substitutes for failed services. We also discuss the consequences of these semantic-enabled approaches and point out required changes for integration in OWL-S.

Towards Extending Service Discovery with Automated Composition Capabilities

In most of research, service composition and discovery are treated separately. In the composition, it is assumed that primitive services are known to the composition component in advance. At the same time, in matchmaking algorithms, usually only one service is considered as a suitable candidate satisfying a query while service combinations are not allowed. The problem is that in realistic composition or mediation scenarios in dynamic environments some specific gap can be bridged only by using a combination of several services which are not known and need to be discovered. We consider such a situation and we propose an approach using a combined match and a composed match. We give a characterization of these two matching types and we develop appropriate matching algorithms.

Efficient Discovery of Collision-Free Service Combinations

Majority of service discovery research considers only primitive services as a suitable match for a given query while service combinations are not allowed. However, many realistic queries cannot be matched by individual services and only a combination of several services can satisfy such queries. Allowing service combinations or proper compositions of primitive services as a valid match introduces problems such as unwanted side-effects (i.e., producing an effect that is not requested), effect duplicities (i.e., producing some effect more than once) and contradictory effects (i.e., producing both an effect and its negation). Also the ranking of matched services has to be reconsidered for service combinations. In this paper, we address all the mentioned issues and present a matchmaking algorithm for retrieval of the best top collision-free service combinations satisfying a given query.

Process Mediation of OWL-S Web Services

The ability to deal with incompatibilities of service requesters and providers is a critical factor for achieving smooth interoperability in dynamic environments. Achieving interoperability of existing web services is a costly process including a lot of development and integration effort which is far from being automated. Semantic Web Services frameworks strive to facilitate flexible dynamic web services discovery, invocation and composition and to support automation of these processes. In this paper we focus on mediation and brokering mechanisms of OWL-S Web Services which we see as the main means to overcome various types of problems and incompatibilities. We describe the process mediation component and the hybrid broker component that present two different approaches to bridge incompatibilities between the requesters and providers interaction protocols.