Mara Nikolaidou

An Integrated Approach to Automated Semantic Web Service Composition through Planning

The paper presents an integrated approach for automated semantic web service composition using AI planning techniques. An important advantage of this approach is that the composition process, as well as the discovery of the atomic services that take part in the composition, are significantly facilitated by the incorporation of semantic information. OWL-S web service descriptions are transformed into a planning problem described in a standardized fashion using PDDL, while semantic information is used for the enhancement of the composition process as well as for approximating the optimal composite service when exact solutions are not found. Solving, visualization, manipulation, and evaluation of the produced composite services are accomplished, while, unlike other systems, independence from specific planners is maintained. Implementation was performed through the development and integration of two software systems, namely PORSCE II and VLEPPO. PORSCE II is responsible for the transformation process, semantic enhancement, and management of the results. VLEPPO is a general-purpose planning system used to automatically acquire solutions for the problem by invoking external planners. A case study is also presented to demonstrate the functionality, performance, and potential of the approach.

Model-based system engineering using SysML: Deriving executable simulation models with QVT

Systems Modeling Language (SysML) is used to define hierarchical system models in model-based engineering (MBE). Although SysML may effectively serve the description of complex systems, it can not effectively support all model-based engineering activities. For example, system validation is usually performed via simulation. In this case, SysML system models should be transformed to domain-specific models, e.g. executable simulation models suitable for specific simulation tools. This paper identifies the key issues for efficient SysML model simulation, utilizing Model Driven Architecture (MDA) concepts. The generation of executable simulation code from SysML system models is considered as a model transformation from the SysML meta-model to the simulation meta-model. Since SysML meta-model is defined using Meta-Object Facility (MOF), the definition of MOF simulation meta-models and the utilization of the Query/View/Transformation (QVT) language for model transformations are analytically discussed. The presented approach is not restricted in a specific simulation framework or type. However, in this paper, the experience obtained from a case study on discrete event simulation is evaluated and the conditions that favor the selection of specific simulation frameworks are identified.

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.

A Specialized Search Engine for Web Service Discovery

Web service discovery on the web is not a trivial task as the number of available web service descriptions continuously increases, and global UDDI registries are no longer available. As discovery through conventional, general-purpose search engines does not yield satisfactory results, a more promising alternative should be explored through specialized search engines. This paper explores the design and implementation of such a framework, resulting in WESS, a search engine targeted to discovering and retrieving web service descriptions. The presented system features an adaptive web service description collection process, through specialized and directed crawling, as well as an enhanced indexing and retrieval mechanism, which handles description documents as semi-structured text, separating actual information from tags and annotations. The paper also presents experiments and use cases regarding different search scenarios, in addition to performance results.

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.

Handling Non-functional Requirements in Information System Architecture Design

Information system architecture design is a complex task depending on both functional and non-functional requirements. Since system architecture definition is strongly related to system performance, non-functional requirements play a significant role during enterprise information system design. To explore the effect of non-functional requirements on system design process, a model-based approach emphasizing non-functional requirements is proposed. To facilitate the designer to effectively define and handle requirements during architecture design, a number of system views are offered, each of them focusing on discrete design issues and satisfying different kind of requirements. A consistent requirement model is defined representing how non-functional requirements are related between them and to system components forming the overall system architecture. SysML has been adopted as the modeling language, since it enables requirement definition and can be formally extended. Moreover, requirement derivation process is discussed and a case study where the proposed concepts are applied in practice while redesigning the legacy system of a large-scale organization is presented.

Introducing a Public Agency Networking Platform towards Supporting Connected Governance

Connected governance constitutes the current trend regarding the provision of electronic governmental services. In the connected governance paradigm, public agencies share objectives across organizational boundaries, as opposed to working solely supporting autonomous portals in the e-government era. The establishment of connected governance poses new requirements, such as cross-organizational connectivity as well as back-office to front-office integration. Towards supporting this concept, we propose a Public Agency Networking Platform (PANP) facilitating personalized cross-organizational services, based on the concept of life events which represent human situations that trigger public services. The key feature of the platform is the simplification of the process execution workflow, as life events are accomplished through a user orchestrated process combining the functionality of discrete public agency applications. Emphasis has been laid on the citizen data protection by adopting a profile mechanism that enables the citizen to administer his/her own data loaded in his/her profile.

Infusing agility in business processes through an event-centric approach

For business processes we consider agility to be the capability to modify and adjust them in the face of unexpected contingencies even during execution phase. Traditional process-centric approaches dictate action sequence definition within the context of a specific business process designed to cover organisations requirements at some former point in time. To address the phenomenon of business processes that fail to match newly evolved organisational needs we propose an event-centric approach identifying meaningful events that drive action execution. We consider actions as autonomous units being aware of only the events initiating them as well as the events they trigger. In that sense, the notion of business process sequence is eliminated; the needed functionality is modelled in a flexible manner in terms of autonomous actions, events and event combinations, promoting the dynamic formation of process instances at execution time. Our approach materialises through a set of methods, named actors-actions-events (AAE), which can be followed as a guide towards identifying the events and actions representing enterprise functionality. Its practical applicability is demonstrated through a simplified example in a medical setting.

A distributed system simulation modelling approach

Abstract The employment of network-based technologies, such as the WWW and middleware platforms, significantly increased the complexity of distributed application, as well as the Quality-of-Service requirements for the underlying network. Distributed application modelling is nowadays far more demanding than network modelling, where numerous solutions are already employed in commercial tools. We introduce a simulation modelling approach for distributed systems, giving emphasis to distributed applications. The proposed scheme enables the in-depth description of application functionality, the accurate estimation of network load and the extension of existing application models to support further customisation. It supports widely employed architectural models, such as the client–server model and its variations, and is based on multi-layer decomposition. Application functionality is described using pre-defined operations, which can be further decomposed into simpler ones, ultimately resulting into elementary actions corresponding to primitive network operations, such as transfer and processing. Even if realisation of this scheme proves to be time demanding, individual application modelling is performed with consistency and considerably lower overhead. The distributed system simulation environment built to realise the proposed modelling scheme and a case study indicating key features of the overall approach are also presented.

A Discipline Approach Towards the Design of Distributed Systems

As the use of Distributed Systems is spreading widely and relevant applications become more demanding, efficient design of Distributed Systems has turned to be a critical issue. For achieving the desirable integration of Distributed System components, knowledge from different areas must be combined leading to increasing complexity. Construction and provision of the appropriate software tools may facilitate the design and evaluation of Distributed Systems architectures. In this paper the architecture and functionality of the Intelligent Distributed System Design tool (IDIS) are presented. IDIS integrates methodologies and techniques from the Artificial Intelligence and Simulation domain, in order to provide a uniform environment for proposing alternative architectural solutions and evaluating their performance.