Georgios-Dimitrios Kapos

PYRAMID-S: a scalable infrastructure for semantic Web service publication and discovery

Web services enhance current Web functionality by altering its nature from document to service-oriented. As the number of Web services increases, it becomes increasingly important to provide a scalable infrastructure of registries that allows both developers and end-users to perform discovery of semantic Web enabled services. The discovery of services needs to be based on QoS characteristics in order to enable result ranking and service selection. Current Web service publication and discovery mechanisms, such as UDDI, either address these issues partially or not at all. In this paper, we build on the enabling technologies of Web services, peer-to-peer and semantic Web in an attempt to address all these important dimensions of service publication and discovery. More specifically, we use a hybrid peer-to-peer topology to organize registries based on domains. In such a model, each registry retains its autonomy, meaning that it can use the publication and discovery mechanisms as well as the ontology of its choice.

A SysML Profile for Classical DEVS Simulators

Discrete event simulation specification (DEVS) is a formalism facilitating hierarchical and modular description of the models executed using DEVS simulators. Lack of standardized, easy-to-use interface enabling simulation practitioners to define their models is an important drawback, since in most cases DEVS models are defined as C++ or Java programs based on existing simulator-specific DEVS libraries. Standard MDA concepts can be applied for the construction of DEVS models executed in different programming environments. DEVS models can be defined using DEVSML, a platform-independent, XML-based format. SysML is proposed as a standardized, graphical representation language of DEVS models stored in DEVSML, consequently transformed into executable code for existing DEVS Simulators, as DEVSJava and DEVSim++. The first step toward this endeavor, is the formal definition of the DEVS SysML profile proposed in this paper.

An integrated framework for automated simulation of SysML models using DEVS

System models are constructed to design, study, and understand complex systems. According to the systems modeling language (SysML) that is a standard for model-based system engineering, all engineering activities should be performed using a common model. To validate complex system models defined in SysML, simulation is usually employed. There are numerous efforts to simulate SysML models using different simulation methods and tools. However, the efficient support of automated generation of executable simulation code is still an issue tangled by the research community. This paper introduces DEVSys, an integrated framework for utilizing existing SysML models and automatically producing executable discrete event simulation code, according to model driven architecture (MDA) concepts. Although this approach is not simulation-specific, discrete event system specification (DEVS) was employed, due to the similarities between SysML and DEVS, mainly in system structure description, and the mature, yet ongoing research on expressing executable DEVS models in a simulator-neutral manner. DEVSys framework elements include (a) a SysML profile for DEVS, enabling integration of simulation capabilities into SysML models, (b) a meta-model for DEVS, allowing the utilization of MDA concepts and tools, (c) a transformation of SysML models to DEVS models, using a standard model transformation language as query/view/transform (QVT), and (d) the generation of DEVS executable code for a DEVS simulation environment with an extensible markup language (XML) interface. The definition and implementation of DEVSys elements, as well as the process for its application are demonstrated and discussed, with the aid of a simple working example.

Integrating simulation capabilities into SysML for enterprise information system design

Performance requirements play a significant role in the design of large-scale systems, such as enterprise information systems. Systems Modeling Language (SysML), proposed by Object Management Group (OMG) for system engineering, provides for requirements specification, though a verification method for quantitative requirements as performance ones is lacking. In the information systems domain, performance requirements are usually verified using simulation. To integrate simulation capabilities into SysML the authors have proposed the concept of the Evaluation View, a discrete diagram to specify enterprise information system architecture under evaluation and the conditions under which performance requirements should be verified. A corresponding SysML profile, called Enterprise Information System (EIS) profile, has been defined. In this paper we present an approach that provides (a) the automated transformation of SysML-based EIS models defined in the Evaluation View to executable simulation code for Discrete Event System Specification (DEVS) simulation environments and (b) the incorporation of simulation results into the original EIS SysML models to enable the verification of corresponding performance requirements.

Seamless Federation of Heterogeneous Service Registries

Web service technology extends the existing web infrastructure by transforming it from a repository of documents to a source of services. As the number of web services increases, the provision of the appropriate service publication and discovery framework is of paramount importance for exploiting the full potential of the web service technology. This paper presents the principles, the functionality and the design of PYRAMID-S, a scalable framework for unified publication and discovery of semantically enhanced services scattered around heterogeneous Registries. It uses a hybrid peer-to-peer topology to organize Registries based on domains. In such a topology, each Registry retains its autonomy, meaning that it can use the publication and discovery mechanisms as well as the ontology of its choice. Furthermore, the discovery of services is based on QoS characteristics in order to enable service selection.

Introducing a UML model for faster-than-real-time simulation

Faster-than-real-time simulation (FRTS) is used when attempting to reach conclusions for the near future. FRTS experimentation proves to be the most demanding phase for conducting FRTS, since it requires concurrent monitoring and management of both the real system and the simulation experiments. Having previously introduced a conceptual methodology and specification for conducting FRTS experiments, we now propose an implementation framework, based on the real time Unified Modeling Language (RT-UML). The derived RT-UML model includes specific timing attributes and is independent of the application examined via FRTS. Thus, implementation of FRTS program modules can be analyzed and realized, following the guidelines of this model, ensuring the reliability of the results within predetermined time frames. A pilot application regarding FRTS implementation based on the proposed RT-UML model and related experience is also discussed in the paper.