Papers by Nikos Papadakis
Applied Sciences, 2020
Key challenges in Internet-of-Things (IoT) system design and management include the secure system... more Key challenges in Internet-of-Things (IoT) system design and management include the secure system composition and the calculation of the security and dependability level of the final system. This paper presents an event-based model-checking framework for IoT systems’ design and management, called CompoSecReasoner. It invokes two main functionalities: (i) system composition verification, and (ii) derivation and validation of security, privacy, and dependability (SPD) metrics. To measure the SPD values of a system, we disassemble two well-known types of security metrics—the attack surface methodologies and the medieval castle approach. The first method determines the attackable points of the system, while the second one defines the protection level that is provided by the currently composed system-of-systems. We extend these techniques and apply the Event Calculus method for modelling the dynamic behavior of a system with progress in time. At first, the protection level of the current...
Correctness of logic programs using proof schemes
International Journal of Knowledge-based and Intelligent Engineering Systems, 2012
Lecture Notes in Computer Science, 2002
The ramification and qualification problems are two infamous, hard and ever present problems in d... more The ramification and qualification problems are two infamous, hard and ever present problems in databases and, more generally, in systems exhibiting a dynamic behavior. The ramification problem refers to determining the indirect effects of actions, whereas the qualification problem refers to determining the preconditions which must hold prior to the execution of an action. A solution to these problems in database systems permits reasoning about the dynamics of databases and allows proving consistency properties. These two problems become increasingly complex in temporal databases and no satisfactory solution has been proposed as of yet. In this paper, we describe these two problems in the context of temporal databases and we propose a solution of polynomial complexity based on the language of the Situation Calculus. This solution extends previous proposals for the solution of these problems in conventional (non-temporal) databases.
Addressing the ramification problem in temporal context: the case of concurrent actions
Proceedings. 15th IEEE International Conference on Tools with Artificial Intelligence
International Journal of Semantic Computing, 2014
The ramification problem in Artificial Intelligence is concerned with the indirect effects of an ... more The ramification problem in Artificial Intelligence is concerned with the indirect effects of an action. It has been shown in previous work that the ramification problem can be solved with the use of integrity constraints and actions representation. In this paper we begin with a quick review of the existing Description Logic Languages, and then we describe a Temporal Extension of Description Logics, able to represent integrity constraints, temporalized actions and non persistent effects. We describe a thorough solution to the ramification problem in Temporal Settings expressed in Temporal Description Logics. The solution also deals with the hard case, in which the effects of an action change the belief about the past.
Lecture Notes in Computer Science, 2009
We introduce TOQL, a query language for querying time information in ontologies. TOQL is a high l... more We introduce TOQL, a query language for querying time information in ontologies. TOQL is a high level query language that handles ontologies almost like relational databases. Queries are issued as SQL-like statements involving time (i.e., time points or intervals) or high-level ontology concepts that vary in time. Although independent from TOQL, this work suggests a mechanism for representing time evolving concepts in ontologies based on the four-dimensional perdurantist mechanism. However, TOQL prevents users from being familiar with the representation of time in ontologies. To show proof of concept, an application has been developed that supports translation and execution of TOQL queries on temporal ontologies combined with a reasoning mechanism based on event calculus. A real world temporal ontology is also implemented on which several TOQL example queries are processed and discussed.
Theoretical Computer Science, 2003
A connection management protocol establishes a connection between two hosts across a wide-area ne... more A connection management protocol establishes a connection between two hosts across a wide-area network to allow reliable message delivery. Following previous work of Kleinberg et al. (Proceedings of the 3rd Israel Symposium on the Theory of Computing and Systems, pp.
Actions with Duration and Constraints: The Ramification Problem in Temporal Databases
International Journal on Artificial Intelligence Tools, 2003
The ramification problem is a hard and ever present problem in systems exhibiting a dynamic behav... more 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 action's execution.
International Journal of Intelligent Systems, 2010
In this paper we study the ramification problem in the setting of temporal databases. Standard so... more 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 assumptions that fluents persist and actions have effects on the subsequent situation only. We provide a solution based on an extension of the situation calculus and the work of McCain and Turner. More specifically, we study the case where there are conflicting effects of actions which executed concurrently, and we distinguish between hard and soft integrity constraints.
Expert Systems with Applications, 2011
We present PROTON, a reasoner for managing temporal information over OWL ontologies. We adopt the... more 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 ie. 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.
Data & Knowledge Engineering, 2006
In this paper we study the ramification problem in the setting of temporal databases. Standard so... more 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.
Action theories in temporal databases
… of the 8th Panhellenic Conference on …, 2001
Abstract. Reasoning about action and change has been one of the main research themes of the knowl... more Abstract. Reasoning about action and change has been one of the main research themes of the knowledge representation and planning communities of the last 15 years. Action theories providing an axiomatic basis for managing change are applicable to a wide area of ...
Hierarchical graph-based media content representation for real time search in large scale multimedia databases
A Tool for Digital Education
International Journal of Semantic Computing, 2018
A method for enhancing the communication between instructor and student is to automate the proced... more A method for enhancing the communication between instructor and student is to automate the procedure of replying to the student’s questions. In order to achieve that, techniques of textual case-based reasoning are used, benefiting both the instructor and the student. The automation of this procedure significantly decreases the workload and involvement required by the tutor. In addition to that, the time required for the students to receive an answer is greatly decreased. In this paper we present such a system, based on pre-existing knowledge, in order to provide answers quickly, for the questions asked by the students.
Expert Systems with Applications, 2010
In this paper, we study the ramification problem in the setting of spatial databases. Standard so... more 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.
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Papers by Nikos Papadakis