Nikos Papadakis

Actions with Duration and Constraints: The Ramification Problem in Temporal Databases

The ramification problem is a hard and ever present problem in systems exhibiting a dynamic behavior. The area of temporal databases in particular is still lacking satisfactory solutions to the ramification problem. In this paper, we address the ramification problem based on causal relationships that take time into account. We study the problem for both instantaneous actions and actions with duration. The proposed solution advances previous work by considering actions with effects occurring in any of the possible future situations resulting from an actions execution.

PROTON: A Prolog Reasoner for Temporal ONtologies in OWL

We present PROTON, a reasoner for managing temporal information over OWL ontologies. We adopt the so called 4d-fluent or 4-dimensionalist approach for representing temporal information in ontologies i.e. for time points or intervals and for events that occur in time points or intervals. Also, we propose an extension to the situation calculus in order to encapsulate time. PROTON is implemented using this extension.

The ramification problem in temporal databases: changing beliefs about the past

In this paper we study the ramification problem in the setting of temporal databases. Standard solutions from the literature on reasoning about action are inadequate because they rely on the assumption that fluents persist, and because actions have effects on the next situation only. In this paper we provide a solution to the ramification problem based on an extension of the situation calculus and the work of McCain and Turner. More specifically, we study the case where the effects of an action refer to the past, a particularly complex problem.

A tool for access to relational databases in natural language

Research highlights? In this paper we present a tool capable of transforming queries formatted in natural languages (English, German and Greek), into their equivalent SQL queries. Also we present an extension of the tool in order to be capable of transforming queries formatted in natural languages (English, German and Greek), into their equivalent SpaRQL queries. Many DB management systems use SQL syntax in order to provide a mechanism for data accessing. Although SQL is widely used, its syntax is not very comprehensive to a typical user. In this paper we present a tool capable of transforming simple queries formatted in natural language into their equivalent SQL queries. The purpose of this study is to provide a query syntax method closer to natural language. We currently support three languages: English, German and Greek and we show how our tool can be extended easily from a user so as to support any other language.

A tool for addressing the ramification problem in spatial databases: A solution implemented in SQL

In this paper, we study the ramification problem in the setting of spatial databases. Standard solutions from the literature on reasoning about action are inadequate because they cannot capture integrity constraints in spatial data. In this paper, we provide a solution to the ramification problem based on situation calculus. We present a tool that connects the theoretical results to practical considerations, by producing the appropriate SQL commands in order to address the ramification problem in spatial databases.

The European Union Higher Education Policy and the Stake of Regionalization

This paper attempts to explore the underlying nature and terms of Higher Education policy. Higher Education policy cannot be viewed outside the changing conditions of the state especially when the inquiry centres on Europe. In the European context, policy making, in order to be efficient, seems to be conducted on two levels, the supranational and the regional. This change in the structure of Higher Education policy making can be considered as an outcome of globalization and the current market economy. The EUs Higher Education policy may be expected to go beyond the national into the supranational level of cooperation with the launching of new initiatives resulting from the Bologna Process and the European Higher Education Area. These initiatives are reshaping the role and responsibilities of Higher Education Institutes towards society and the market. The new role that these institutes are called upon to play indicates a clear tendency towards dissemination and the growing need for cooperation at the regional level.

EvoRDF: A Framework for Exploring Ontology Evolution

The evolution of ontologies is a reality in current research community. The problem of understanding and exploring this evolution is a fundamental problem as maintainers of depending artifacts need to take a decision about possible changes and ontology engineers need to understand the reasons for this evolution. Recent research focuses on identifying and statically visualizing deltas between ontology versions using various low- or high-level language of changes. In this paper, we argue that this is not enough and we provide a complete solution enabling the active, dynamic exploration of the evolution of RDF/S ontologies using provenance queries. To this direction, we construct an ontology of changes for modeling the language of changes and we store all changes as instances of this ontology in a triple store. On top of this triple store two visualization modules, one individual app and one protege plugin allow the exploration of the evolution using provenance queries. To the best of our knowledge our approach is unique in allowing the dynamic exploration of the evolution using provenance queries.

A Reasoning System for Composition Verification and Security Validation

The procedure to prove that a system-of-systems is composable and secure is a very difficult task. Formal methods are mathematically-based techniques used for the specification, development and verification of software and hardware systems. This paper presents a model-based framework for dynamic embedded system composition and security evaluation. Event Calculus is applied for modeling the security behavior of a dynamic system and calculating its security level with the progress in time. The framework includes two main functionalities: composition validation and derivation of security and performance metrics and properties. Starting from an initial system state and given a series of further composition events, the framework derives the final system state as well as its security and performance metrics and properties. We implement the proposed framework in an epistemic reasoner, the rule engine JESS with an extension of DECKT for the reasoning process and the JAVA programming language.

A knowledge-based interactive verifier for logic programs

This paper presents an interactive verifier for logic programs. These logic programs are constructed by a schema-based method. Each program is associated with proof schemes due to the program development method. The correctness proof of a program is guided by its associated proof schemes. The main components of the verifier are the prover which carries out the proof steps, the knowledge base (KB) which includes representations of all theories and transformation rules, the KB update which supports the update of KB and the graphical user interface (GUI). The emphasis in the design of this proof checker is on effective guidance of the proof based on the activated proof schemes and on performance by the verifier of tedious, trivial and time consuming tasks. The difficult proof decisions are taken by the user, then, the proof checker applies them. The design of the interface is based on providing the user the required support for the proof of a theorem and for the update of KB. This system is an effective and useful tool for the interactive verification of non-trivial logic programs.

Constraint satisfaction in XML temporal databases

In this paper we elaborate on the handling of the ramification problem in the setting of temporal databases. Starting with the observation that solutions from the literature on reasoning about action are inadequate for addressing the ramification problem. The ramification problem refers to the production of indirect effects after the execution of an update in order to ensure the satisfaction of integrity constraints (an update could has as effect the violation of some integrity constraints). In our prior work we have presented a solution (with implementation) based on an extension of the situation calculus and the work of McCain and Turner. In this paper, we present a tool that connects the theoretical results to practical considerations, by (a) producing the appropriate static rules in order to address the ramification problem in temporal setting and (b) providing a friendly enviroment which produces the indirect effects after the execution of an xquery in XML temporal databases.