Ilias Sakellariou | University of Macedonia (original) (raw)

Papers by Ilias Sakellariou

Proceedings of the 15th International Conference on Agents and Artificial Intelligence

Lecture Notes in Computer Science, 2014

Artificial Intelligence: …, Jan 1, 1998

The management of large data networks, like a national WAN, is without any doubt a complex task. ... more The management of large data networks, like a national WAN, is without any doubt a complex task. Taking into account the constantly increasing size and complexity of today's TCP/IP based networks, it becomes obvious that there is a demanding need for better than simple monitoring management tools. Expert system technology seems to be a very promising approach for the development of such tools. This paper describes the system architecture of ExperNet, a distributed expert system for the management of the National Computer Network of Ukraine, and the implementation of the tools used for its development. ExperNet is a multiagent system built in DEVICE, an active OODB enhanced with high level rules, that uses CS-Prolog II to implement the communication facilities required. The system employs HNMS+ and Big-Brother, two modi ed versions of existing network management tools, in order to obtain a complete view of the monitored network.

This application paper presents MYVISITPLANNERGR, an intelligent web-based system aiming at makin... more This application paper presents MYVISITPLANNERGR, an intelligent web-based system aiming at making recommendations that help visitors and residents of the region of Northern Greece to plan their leisure, cultural and other activities during their stay in this area. The system encompasses a rich ontology of activities, categorized across dimensions such as activity type, historical era, user profile and age group. Each activity is characterized by attributes describing its location, cost, availability and duration range. The system makes activity recommendations based on user-selected criteria, such as visit duration and timing, geographical areas of interest and visit profiling. The user edits the proposed list and the system creates a plan, taking into account temporal and geographical constraints imposed by the selected activities, as well as by other events in the user’s calendar. The user may edit the proposed plan or request alternative plans. A recommendation engine employs non-intrusive machine learning techniques to dynamically infer and update the user’s profile, concerning his preferences for both activities and resulting plans, while taking privacy concerns into account. The system is coupled with a module to semi-automatically feed its database with new activities in the area.

… Conference on Informatics …

The X-machine formal method forms the basis for a specification/modeling language with a substant... more The X-machine formal method forms the basis for a specification/modeling language with a substantial potential value to software engineers. An X-machine is a more expressive and flexible state machine, capable of modeling both the dynamic and the static aspect of a system. Communicating X-machines provide a methodology for building communicating systems out of existing stand-alone X-machines. However, for practically using the model in an real-world system development process, a tool for demonstrating and informally verifying the properties of the modeled system is required. An ideal platform for efficiently implementing such a tool, should support, process oriented programming, efficient communication primitives and declarativeness. Cspcons is a distributed CLP platform that supports program execution over multiple independent sequential CLP processes that synchronize though message and event passing. The present paper demonstrates the applicability of the Cspcons programming model to the implementation of a communicating X-machine animator tool that will act as the basis for an extended set of tools that will support the formal mathematical analysis of the specified X-machine models.

users.uom.gr

The area of distributed constraint satisfaction has drawn significant attention in the past decad... more The area of distributed constraint satisfaction has drawn significant attention in the past decade. The approaches proposed in the area can be classified in two large categories: distributed search techniques and distributed filtering techniques. The work described in this paper concerns the CLP implementation of the Dis-SAC algorithm, a novel distributed filtering technique that is based on the singleton consistency algorithm. The advantages of the algorithm include a high pruning efficiency and a remarkable simplicity. The latter allows an unproblematic implementation of the algorithm in any constraint programming platform that supports network communication, without the need of tampering with the (low level) consistency algorithm employed. The present paper briefly describes Dis-SAC along with its implementation in the Cspcons distributed CLP platform and presents experimental results on a number of structured constraint problems. The motivation behind this work is twofold: to support our argument concerning the simple implementation of the algorithm and to further investigate the benefits of its application to constraint satisfaction problems.

Engineering Intelligent Systems, 2012

Multi-Agent Systems for …, 2010

ABSTRACT In the context of an Agent and Multi-Agent Systems course, exposing students to problems... more ABSTRACT In the context of an Agent and Multi-Agent Systems course, exposing students to problems and issues related to agent-based programming allows them to understand at a deeper level the otherwise theoretical aspects involved in the design of a multi-agent ...

users.uom.gr

Agent based modelling has received significant attention in the recent years mainly due its wide ... more Agent based modelling has received significant attention in the recent years mainly due its wide adoption by scientists in a number of fields. Although agent simulation platforms have proven to be quite mature and expressive for modelling simple agents, little has been done regarding enhancing these platforms by higher level agent oriented programming facilities. This work aims at this direction, i.e. an add-on library to a well known simulation platform aiming at the specification of complex high level agents, using state machines.

Artificial Intelligence Applications and …, 2011

Recycling has been gaining ground, thanks to the recent progress made in the related technology. ... more Recycling has been gaining ground, thanks to the recent progress made in the related technology. However, a limiting factor to its wide adoption, is the lack of modern tools for managing the collection of recyclable resources. In this paper, we present EcoTruck, a ...

Proceedings of Informatics …, 2008

In the context of an Agent and Multi-Agent Systems course, satisfying the students demands for ha... more In the context of an Agent and Multi-Agent Systems course, satisfying the students demands for hands-on practice presents an interesting challenge. Educators have reported a variety of environments and techniques they use in order to increase active learning. In this paper we record our experience using NetLogo as part of the practical coursework that students need to carry out within an Intelligent Agents course. We argue that NetLogo meets most of the requirements that suit our criteria. In addition, we describe two extra NetLogo libraries provided to students, one for BDI-like agents (goal-oriented agents) and one for ACL-like (Agent Communication Language) communication. We present a few scenarios that we use in coursework handouts and how the partially developed environment we provide for each scenario facilitates practical agent design and simulation, thus satisfying the learning outcomes of the practical work and the course as a whole.

Proceeding of 8th …, 2009

In the context of an Intelligent Agents course, we have chosen NetLogo as the means to satisfy th... more In the context of an Intelligent Agents course, we have chosen NetLogo as the means to satisfy the students' demand for hands-on practice, to help them understand at a deeper level the otherwise theoretical aspects involved in the design of a multi-agent system (MAS). In this paper we present in detail the structure of the two pieces of coursework assigned to the students, the first one introducing students to the reactive architecture and the second, building on the first, to the hybrid architecture, also incorporating agent communication issues and interaction protocols. More particularly, we present an indicative MAS scenario that is given to the students as a case study for investigation as well as a thorough description of what is expected from them. The scenario facilitates practical agent design and simulation, contributes to the expected learning outcomes and provides various assessment opportunities.

Although agent based modelling has drawn significant attention in the recent years, with a signif... more Although agent based modelling has drawn significant attention in the recent years, with a significant number of simulation platforms proposed, the latter target usually relatively simple reactive agents. Thus, little has been done toward enhancing the modelling capabilities of platforms with richer agent oriented programming constructs that could potentially lead to the implementation of more sophisticated models. This paper presents an extension to the TSTATES library that aims to support the implementation of state based intelligent agents and a more complex example drawn from the pedestrian simulation domain that demonstrates the potential of the library in programming complex agent systems.

Current Trends in …, 2007

Social insect colonies present an interesting problem for formal modelling due to their outstandi... more Social insect colonies present an interesting problem for formal modelling due to their outstanding characteristics, such as self-organisation and emergence. In this paper, we experiment with two different formal methods, Communicating X-machines and Population P Systems, which can be used separately to model biologically inspired. systems. The case of Pharaoh's ants is used as a vehicle of study. We discuss the advantages of each method and we present a framework that leads to a rapid implementation and simulation of such multiagent systems.

Constraint programming occupies territory that might previously have been considered the province... more Constraint programming occupies territory that might previously have been considered the province of declarative programming or even expert systems. These are frameworks for solving problems in artificial intelligence that can be stated as heu more...

Proceedings of the 12th …, 2003

The work presented in this paper concerns the application of CSPCONS, a distributed constraint lo... more The work presented in this paper concerns the application of CSPCONS, a distributed constraint logic programming platform to a workforce management problem, namely the BT-250-118 problem instance. The latter is a well-studied problem instance in which the requirement is to create sequences of job locations for the technicians to visit (tours), so as to serve as many jobs as possible, minimizing at the same time the travel duration. CSPCONS is a logic programming platform that supports program execution over multiple Prolog processes with constraints. It offers channel-based communicating processes and TCP/IP communication and is based on the CSP model introduced by Hoare. This paper demonstrates its applicability to such complex Distributed Constraint Satisfaction problems.

Journal of Experimental and Theoretical Artificial Intelligence, 2012

This article presents a systematic and complete algorithm to compute all higher order exclusion r... more This article presents a systematic and complete algorithm to compute all higher order exclusion relations for a propositional planning problem, that is, sets of propositions that cannot hold simultaneously at specific time points, without any bound on the order of the exclusion relations. This algorithm is proved to allow for backtrack-free plan extraction, provided that all goals have to be achieved simultaneously. In particular, levelled global consistency is achieved, i.e. all exclusion relations between propositions within each time step are computed. However, achieving levelled global consistency is impractical for most non-trivial planning problems. Indeed, as our empirical evaluation over a variety of planning problems suggests, best performance is achieved when setting a bound on the order of the computed exclusion relations and using search to extract a plan. Additional statistics extracted from our experiments shed light on the internal dynamics of Graphplan-style planners.

Proceedings of ALA2012, Adaptive …, 2012

We present autonomous agents that are designed without encoding strategies or knowledge of the en... more We present autonomous agents that are designed without encoding strategies or knowledge of the environment in the agent. The design approach focuses on the notion of sensorimotor patterns of interaction between the agent and the environment rather than separating perception from action. The agent's motivational system is also interaction-centered in that the agent has inborn proclivities to enact certain sensorimotor patterns and to avoid others. Such motivations result in the agent autonomously discovering, learning, and exploiting regularities of interaction afforded by the environment, and constructing operative knowledge of the environment. Because such agents have no predefined goals, we propose a set of behavioral criteria to both judge and demonstrate the agents' capacities, rather than performance measurement. A design platform based on NetLogo is presented. Results show that these agents demonstrate interesting behavioral properties such as hedonistic temperance, active perception, and individuation.

Informatics, 2009. BCI'09. …, 2009

The Web Ontology Language (OWL) is one of the fundamental blocks for realizing the Semantic Web v... more The Web Ontology Language (OWL) is one of the fundamental blocks for realizing the Semantic Web vision, since it allows to represent probably the most difficult component of the latter; knowledge regarding the concepts of domain of discourse, i.e. ontologies. Unfortunately, its expressive power goes in hand with a rather verbose syntax, difficult to be understood by non-technical users, and thus leading to difficulties in validation and verification of the represented knowledge. A translation tool from OWL to some form of natural language could significantly assist users towards such tasks. Such a tool requires correctly interpreting the ontology constructs, representing highly nested ontologies, and forming logical sentences. This paper presents an innovative approach to directly translating RDF/XML based structured ontology into error free concise natural language text akin to English.

Proceedings of the 15th International Conference on Agents and Artificial Intelligence

Lecture Notes in Computer Science, 2014

Artificial Intelligence: …, Jan 1, 1998

The management of large data networks, like a national WAN, is without any doubt a complex task. ... more The management of large data networks, like a national WAN, is without any doubt a complex task. Taking into account the constantly increasing size and complexity of today's TCP/IP based networks, it becomes obvious that there is a demanding need for better than simple monitoring management tools. Expert system technology seems to be a very promising approach for the development of such tools. This paper describes the system architecture of ExperNet, a distributed expert system for the management of the National Computer Network of Ukraine, and the implementation of the tools used for its development. ExperNet is a multiagent system built in DEVICE, an active OODB enhanced with high level rules, that uses CS-Prolog II to implement the communication facilities required. The system employs HNMS+ and Big-Brother, two modi ed versions of existing network management tools, in order to obtain a complete view of the monitored network.

This application paper presents MYVISITPLANNERGR, an intelligent web-based system aiming at makin... more This application paper presents MYVISITPLANNERGR, an intelligent web-based system aiming at making recommendations that help visitors and residents of the region of Northern Greece to plan their leisure, cultural and other activities during their stay in this area. The system encompasses a rich ontology of activities, categorized across dimensions such as activity type, historical era, user profile and age group. Each activity is characterized by attributes describing its location, cost, availability and duration range. The system makes activity recommendations based on user-selected criteria, such as visit duration and timing, geographical areas of interest and visit profiling. The user edits the proposed list and the system creates a plan, taking into account temporal and geographical constraints imposed by the selected activities, as well as by other events in the user’s calendar. The user may edit the proposed plan or request alternative plans. A recommendation engine employs non-intrusive machine learning techniques to dynamically infer and update the user’s profile, concerning his preferences for both activities and resulting plans, while taking privacy concerns into account. The system is coupled with a module to semi-automatically feed its database with new activities in the area.

… Conference on Informatics …

The X-machine formal method forms the basis for a specification/modeling language with a substant... more The X-machine formal method forms the basis for a specification/modeling language with a substantial potential value to software engineers. An X-machine is a more expressive and flexible state machine, capable of modeling both the dynamic and the static aspect of a system. Communicating X-machines provide a methodology for building communicating systems out of existing stand-alone X-machines. However, for practically using the model in an real-world system development process, a tool for demonstrating and informally verifying the properties of the modeled system is required. An ideal platform for efficiently implementing such a tool, should support, process oriented programming, efficient communication primitives and declarativeness. Cspcons is a distributed CLP platform that supports program execution over multiple independent sequential CLP processes that synchronize though message and event passing. The present paper demonstrates the applicability of the Cspcons programming model to the implementation of a communicating X-machine animator tool that will act as the basis for an extended set of tools that will support the formal mathematical analysis of the specified X-machine models.

users.uom.gr

The area of distributed constraint satisfaction has drawn significant attention in the past decad... more The area of distributed constraint satisfaction has drawn significant attention in the past decade. The approaches proposed in the area can be classified in two large categories: distributed search techniques and distributed filtering techniques. The work described in this paper concerns the CLP implementation of the Dis-SAC algorithm, a novel distributed filtering technique that is based on the singleton consistency algorithm. The advantages of the algorithm include a high pruning efficiency and a remarkable simplicity. The latter allows an unproblematic implementation of the algorithm in any constraint programming platform that supports network communication, without the need of tampering with the (low level) consistency algorithm employed. The present paper briefly describes Dis-SAC along with its implementation in the Cspcons distributed CLP platform and presents experimental results on a number of structured constraint problems. The motivation behind this work is twofold: to support our argument concerning the simple implementation of the algorithm and to further investigate the benefits of its application to constraint satisfaction problems.

Engineering Intelligent Systems, 2012

Multi-Agent Systems for …, 2010

ABSTRACT In the context of an Agent and Multi-Agent Systems course, exposing students to problems... more ABSTRACT In the context of an Agent and Multi-Agent Systems course, exposing students to problems and issues related to agent-based programming allows them to understand at a deeper level the otherwise theoretical aspects involved in the design of a multi-agent ...

users.uom.gr

Agent based modelling has received significant attention in the recent years mainly due its wide ... more Agent based modelling has received significant attention in the recent years mainly due its wide adoption by scientists in a number of fields. Although agent simulation platforms have proven to be quite mature and expressive for modelling simple agents, little has been done regarding enhancing these platforms by higher level agent oriented programming facilities. This work aims at this direction, i.e. an add-on library to a well known simulation platform aiming at the specification of complex high level agents, using state machines.

Artificial Intelligence Applications and …, 2011

Recycling has been gaining ground, thanks to the recent progress made in the related technology. ... more Recycling has been gaining ground, thanks to the recent progress made in the related technology. However, a limiting factor to its wide adoption, is the lack of modern tools for managing the collection of recyclable resources. In this paper, we present EcoTruck, a ...

Proceedings of Informatics …, 2008

In the context of an Agent and Multi-Agent Systems course, satisfying the students demands for ha... more In the context of an Agent and Multi-Agent Systems course, satisfying the students demands for hands-on practice presents an interesting challenge. Educators have reported a variety of environments and techniques they use in order to increase active learning. In this paper we record our experience using NetLogo as part of the practical coursework that students need to carry out within an Intelligent Agents course. We argue that NetLogo meets most of the requirements that suit our criteria. In addition, we describe two extra NetLogo libraries provided to students, one for BDI-like agents (goal-oriented agents) and one for ACL-like (Agent Communication Language) communication. We present a few scenarios that we use in coursework handouts and how the partially developed environment we provide for each scenario facilitates practical agent design and simulation, thus satisfying the learning outcomes of the practical work and the course as a whole.

Proceeding of 8th …, 2009

In the context of an Intelligent Agents course, we have chosen NetLogo as the means to satisfy th... more In the context of an Intelligent Agents course, we have chosen NetLogo as the means to satisfy the students' demand for hands-on practice, to help them understand at a deeper level the otherwise theoretical aspects involved in the design of a multi-agent system (MAS). In this paper we present in detail the structure of the two pieces of coursework assigned to the students, the first one introducing students to the reactive architecture and the second, building on the first, to the hybrid architecture, also incorporating agent communication issues and interaction protocols. More particularly, we present an indicative MAS scenario that is given to the students as a case study for investigation as well as a thorough description of what is expected from them. The scenario facilitates practical agent design and simulation, contributes to the expected learning outcomes and provides various assessment opportunities.

Although agent based modelling has drawn significant attention in the recent years, with a signif... more Although agent based modelling has drawn significant attention in the recent years, with a significant number of simulation platforms proposed, the latter target usually relatively simple reactive agents. Thus, little has been done toward enhancing the modelling capabilities of platforms with richer agent oriented programming constructs that could potentially lead to the implementation of more sophisticated models. This paper presents an extension to the TSTATES library that aims to support the implementation of state based intelligent agents and a more complex example drawn from the pedestrian simulation domain that demonstrates the potential of the library in programming complex agent systems.

Current Trends in …, 2007

Social insect colonies present an interesting problem for formal modelling due to their outstandi... more Social insect colonies present an interesting problem for formal modelling due to their outstanding characteristics, such as self-organisation and emergence. In this paper, we experiment with two different formal methods, Communicating X-machines and Population P Systems, which can be used separately to model biologically inspired. systems. The case of Pharaoh's ants is used as a vehicle of study. We discuss the advantages of each method and we present a framework that leads to a rapid implementation and simulation of such multiagent systems.

Constraint programming occupies territory that might previously have been considered the province... more Constraint programming occupies territory that might previously have been considered the province of declarative programming or even expert systems. These are frameworks for solving problems in artificial intelligence that can be stated as heu more...

Proceedings of the 12th …, 2003

The work presented in this paper concerns the application of CSPCONS, a distributed constraint lo... more The work presented in this paper concerns the application of CSPCONS, a distributed constraint logic programming platform to a workforce management problem, namely the BT-250-118 problem instance. The latter is a well-studied problem instance in which the requirement is to create sequences of job locations for the technicians to visit (tours), so as to serve as many jobs as possible, minimizing at the same time the travel duration. CSPCONS is a logic programming platform that supports program execution over multiple Prolog processes with constraints. It offers channel-based communicating processes and TCP/IP communication and is based on the CSP model introduced by Hoare. This paper demonstrates its applicability to such complex Distributed Constraint Satisfaction problems.

Journal of Experimental and Theoretical Artificial Intelligence, 2012

This article presents a systematic and complete algorithm to compute all higher order exclusion r... more This article presents a systematic and complete algorithm to compute all higher order exclusion relations for a propositional planning problem, that is, sets of propositions that cannot hold simultaneously at specific time points, without any bound on the order of the exclusion relations. This algorithm is proved to allow for backtrack-free plan extraction, provided that all goals have to be achieved simultaneously. In particular, levelled global consistency is achieved, i.e. all exclusion relations between propositions within each time step are computed. However, achieving levelled global consistency is impractical for most non-trivial planning problems. Indeed, as our empirical evaluation over a variety of planning problems suggests, best performance is achieved when setting a bound on the order of the computed exclusion relations and using search to extract a plan. Additional statistics extracted from our experiments shed light on the internal dynamics of Graphplan-style planners.

Proceedings of ALA2012, Adaptive …, 2012

We present autonomous agents that are designed without encoding strategies or knowledge of the en... more We present autonomous agents that are designed without encoding strategies or knowledge of the environment in the agent. The design approach focuses on the notion of sensorimotor patterns of interaction between the agent and the environment rather than separating perception from action. The agent's motivational system is also interaction-centered in that the agent has inborn proclivities to enact certain sensorimotor patterns and to avoid others. Such motivations result in the agent autonomously discovering, learning, and exploiting regularities of interaction afforded by the environment, and constructing operative knowledge of the environment. Because such agents have no predefined goals, we propose a set of behavioral criteria to both judge and demonstrate the agents' capacities, rather than performance measurement. A design platform based on NetLogo is presented. Results show that these agents demonstrate interesting behavioral properties such as hedonistic temperance, active perception, and individuation.

Informatics, 2009. BCI'09. …, 2009

The Web Ontology Language (OWL) is one of the fundamental blocks for realizing the Semantic Web v... more The Web Ontology Language (OWL) is one of the fundamental blocks for realizing the Semantic Web vision, since it allows to represent probably the most difficult component of the latter; knowledge regarding the concepts of domain of discourse, i.e. ontologies. Unfortunately, its expressive power goes in hand with a rather verbose syntax, difficult to be understood by non-technical users, and thus leading to difficulties in validation and verification of the represented knowledge. A translation tool from OWL to some form of natural language could significantly assist users towards such tasks. Such a tool requires correctly interpreting the ontology constructs, representing highly nested ontologies, and forming logical sentences. This paper presents an innovative approach to directly translating RDF/XML based structured ontology into error free concise natural language text akin to English.

SETN 2020: 11th Hellenic Conference on Artificial Intelligence, 2020

Load balancing is a widely used technique that aims to enable large network topologies, most com... more Load balancing is a widely used technique that aims to enable large network topologies, most commonly found in large data centers, to handle the constantly varying load of service requests. Traditional networks built on multi-vendor hardware and software present significant difficulties in the efficient and flexible application of load balancing techniques. Usually, solutions rely on high cost dedicated hardware and thus are used only for a subset of the tasks, resulting to limited flexibility for network administrators. Software Defined Networking (SDN) is a relatively new approach that enables flexible network management solutions to a number of problems, including that of efficient load-balancing. The key characteristics of decoupled centralized network control combined with programmability, allows the seamless integration of AI techniques to network management. Toward this direction, this paper employs deep reinforcement learning to effectively load balance requests to services in a data center network, resulting to an approach that is able to dynamically adapt to varying request loads, including changes in the infrastructure’s capabilities. The proposed approach is experimentally evaluated in order to support its feasibility, with very promising results.