Dimitris Vrakas | Aristotle University of Thessaloniki (original) (raw)

Papers by Dimitris Vrakas

ArXiv, 2021

Localization is a crucial task for autonomous mobile robots in order to successfully move to goal... more Localization is a crucial task for autonomous mobile robots in order to successfully move to goal locations in their environment. Usually this is done in a robot-centric manner, where the robot maintains a map with its body in the center. In swarm robotics applications, where a group of robots need to coordinate in order to achieve their common goals, robot-centric localization will not suffice as each member of the swarm has its own frame of reference. One way to deal with this problem is to create, maintain and share a common map (global coordinate system), among the members of the swarm. This paper presents an approach to global localization for a group of robots in unknown, GPS and landmark free environments that extends the localization scheme of the LadyBug algorithm [1]. The main idea relies on members of the swarm stay still and act as beacons, emitting electromagnetic signals. These stationary robots form a global frame of reference and the rest of the group localize themse...

Neural Computing and Applications

Artificial Intelligence Review

In domain independent heuristic planning there is a number of planning systems with very good per... more In domain independent heuristic planning there is a number of planning systems with very good performance on some problems and very poor on others. Few attempts have been made in the past to explain this phenomenon. In this paper we use machine learning techniques to discover knowledge hidden in the dynamics of the planning process that would relate specific characteristics of a planning problem with specific properties of a planning system that lead to good or bad performance. By this, we aim at shedding light to some of the dark areas of heuristic planning and develop an adaptive planner that would be able to optimize its configuration according to the problem at hand.

This article presents a detailed survey on Artificial Intelligent approaches, that combine Reinfo... more This article presents a detailed survey on Artificial Intelligent approaches, that combine Reinforcement Learning and Automated Planning. There is a close relationship between those two areas as they both deal with the process of guiding an agent, situated in a dynamic environment, in order to achieve a set of predefined goals. Therefore, it is straightforward to integrate learning and planning, in a single guiding mechanism and there have been many approaches in this direction during the past years. The approaches are organized and presented according to various characteristics, as the used planning mechanism or the reinforcement learning algorithm.

Journal of Ambient Intelligence and Smart Environments, 2016

This paper presents a novel, integrated platform for energy monitoring, management and savings in... more This paper presents a novel, integrated platform for energy monitoring, management and savings in the context of a Smart University Building. Namely, the proposed Smart International Hellenic University (IHU) platform integrates an intelligent, rule-based agent that enforces savings, while a variety of applications offers user interaction with the system and the means for monitoring and management. The application layer is built over a common Web Service middleware, incorporating semantic interoperability. Monitoring applications visualize raw and aggregated sensor readings, such as building energy disaggregation, environmental measurements and data center efficiency. Extensive monitoring capabilities allow users to take immediate action and devise policies towards energy-savings. Such policies are, then, autonomously enforced by the intelligent, hybrid agent, which is capable of both deliberative (long-term) and reactive (immediate) actions. The agent is also integrated with the Open-ADR standard for receiving provider instructions in future Smart Grids. A pilot deployment of the agent with expert-formulated policies at the IHU premises, has managed to reduce the total daily consumption of a typical university office by approximately 16%.

Proceedings of the 9th Hellenic Conference on Artificial Intelligence - SETN '16, 2016

This paper presents PGRT, a parallel version of a best first planner based on the Greedy Regressi... more This paper presents PGRT, a parallel version of a best first planner based on the Greedy Regression Tables approach. The parallelization method of PGRT distributes the task of extracting applicable actions to a given state among the available processors. Although the number of operators limits the scalability of PGRT, it has proven to be quite efficient for low scale parallelization. A modified Operator Reordering method has been used in order to achieve further increase in the efficiency of the parallel algorithm. We illustrate the speedup of PGRT on a variety of hard logistics problems, adopted from the AIPS-98 planning competition.

Service level agreements (SLAs) are powerful instruments for describing all obligations and expec... more Service level agreements (SLAs) are powerful instruments for describing all obligations and expectations in a business relationship. It is of focal importance for deploying Grid technology to commercial applications. The EC-funded project HPC4U (Highly Predictable Clusters for Internet Grids) aimed at introducing SLA-awareness in local resource management systems, while the EC-funded project AssessGrid introduced the notion of risk, which is associated with every business contract. This paper highlights the concept of planning based resource management and describes the SLA-aware scheduler developed and used in these projects.

This paper presents the design and development of an adaptive planning system using the technolog... more This paper presents the design and development of an adaptive planning system using the technology of Web services. The Web-based adaptive planning system consists of two modules that can work independently. The first one is called HAP-WS and is the Web service interface to the domain independent planner HAP (Highly Adjustable Planner) that can be customized through the adjustment of several parameters, either manually or automatically. In the manual mode, the user itself adjusts planner parameters giving explicitly the values. In the automatic mode, the second subsystem, called LAMP-WS, computes the values of the planning parameters of HAP. LAMP-WS is the Web service interface to the learning system LAMP (Lazy Adaptive Multicriteria Planning) that can automatically configure a planning system using instance-based learning on past performance data of that system. The two subsystems are implemented as independent Web services, which can be used stand-alone and reside in different servers in potentially different geographical locations. This paper presents the design and development of a Web-based system for Adaptive Planning that utilizes the technology of Web services. The system consists of two independent Web services: HAP-WS is a Web service interface to the HAP (Highly Adjustable Planner) planning system [14]. A user or program can directly use HAP-WS by providing it the planning domain and problem definition files, and optionally the values for its 7 planning parameters. LAMP-WS is a Web service interface to the LAMP (Lazy Adaptive Multicriteria Planning) learning system [12] that predicts a configuration for the planning parameters of HAP based on the characteristics of the given planning problem. LAMP-WS can also be used directly by a user or program for consultation on a suitable parameter configuration for the HAP planner. For automatically configuring HAP, a combination of the two services is required, which can be easily handled by a suitable client application. Such an application example developed in ASP.NET is also presented in this paper. The rest of the paper is organized as follows. Section 2 presents a brief reference to the technologies that the Web service architecture entails. Section 3 introduces the concept of Adaptive Planning and related work. Section 4 describes the Web services that were developed for the purposes of Adaptive Planning and Section 5 presents an example ASP.NET application that uses these Web services. Finally the last section concludes this work and points areas for improvements.

Lecture Notes in Computer Science, 2014

IEEE Transactions on Services Computing, 2015

This work aims to resolve issues related to Web Service retrieval, also known as Service Selectio... more This work aims to resolve issues related to Web Service retrieval, also known as Service Selection, Discovery or essentially Matching, in two directions. Firstly, a novel matching algorithm for SAWSDL is introduced. The algorithm is hybrid in nature, combining novel and known concepts, such as a logic-based strategy and syntactic text-similarity measures on semantic annotations and textual descriptions. A plugin for the S3 contest environment was developed, in order to position Tomaco amongst state-of-the-art in an objective, reproducible manner. Evaluation showed that Tomaco ranks high amongst state of the art, especially for early recall levels. Secondly, this work introduces the Tomaco web application, which aims to accelerate the widespread adoption of Semantic Web Service technologies and algorithms while targeting the lack of userfriendly applications in this field. Tomaco integrates a variety of configurable matching algorithms proposed in this paper. It, finally, allows discovery of both existing and user-contributed service collections and ontologies, serving also as a service registry.

Lecture Notes in Computer Science, 2002

This paper proposes a domain independent heuristic for state space planning, which is based on ac... more This paper proposes a domain independent heuristic for state space planning, which is based on action evaluation. The heuristic obtains estimates for the cost of applying each action of the domain by performing a forward search in a relaxed version of the initial problem. The estimates for the actions are then utilized in a backward search on the original problem. The heuristic, which has been further refined by a goal-ordering technique, has been implemented in AcE (Action Evaluation), a state space heuristic planner, and thoroughly tested on a variety of toy problems.

Artificial Intelligence for Advanced Problem Solving Techniques, 2008

This chapter proposes a new method to obtain optimal solution using satisfactory approach in unce... more This chapter proposes a new method to obtain optimal solution using satisfactory approach in uncertain environment. The optimal solution is obtained by using possibilistic linear programming approach and intelligent computing by MATLAB?. The optimal solution for profit function, index quality and worker satisfaction index in construction industry is considered. Decision maker and implementer tabulate the final possibilistic and realistic outcome for objective functions respect to level of satisfaction and vagueness for forecasting and planning. When the decision maker finds the optimum parameters with acceptable degree of satisfaction, he/she can apply the confidence of gaining much profit in terms of helping the public with high quality and least cost products. The proposed fuzzy membership function allows the implementer to find a better arrangement for the equipments in the production line to fulfill the wanted products in an optimum way.

Proceedings of the 2nd International Conference on Web Intelligence, Mining and Semantics - WIMS '12, 2012

In this paper, we describe the architecture and functionality of IRISPortal, a semantic portal th... more In this paper, we describe the architecture and functionality of IRISPortal, a semantic portal that allows the management of industrial risk cases by exploiting state-of-the-art semantic technologies, such as the OWL 2 language and the OWLIM semantic repository. The portal allows the web-based management of risk cases that are modeled in terms of a risk ontology, assisting the domain experts to perform administrative tasks, such as adding, deleting and updating risk cases. Furthermore, the portal provides the functionality to the end-users for searching and browsing the modeled risk cases and their corresponding characteristics, based on the semantic relationships that derive from the ontology model after the reasoning procedure.

International Journal on Artificial Intelligence Tools, 2015

Web service composition is a significant problem as the number of available web services increase... more Web service composition is a significant problem as the number of available web services increases; however, manual composition is not an efficient option. Automated web service composition can be performed using AI Planning techniques, utilizing descriptions of available atomic web services, enhanced with semantic awareness and relaxation. This paper discusses a unified, semantically aware approach, handling both semantic (OWL-S & SAWSDL) and non-semantic (WSDL) web service descriptions. In the first case, ontology analysis is adopted to semantically enhance the planning domains and problems, in order to deal with cases where exact syntactic input-to-output matching is not feasible. In the non-semantic descriptions case, semantic information is acquired utilizing alternative sources such as lexical thesauri. Concept similarity measures are applied and utilized to achieve the desired degree of semantic relaxation. The solution to a web service composition problem is a plan describin...

Lecture Notes in Computer Science, 2008

This paper presents a prototype system that exploits planning and an ontology concept ranking alg... more This paper presents a prototype system that exploits planning and an ontology concept ranking algorithm for composing semantic Web services (PORSCE). The system exploits the inferencing capabilities of a Description Logics Reasoner in order to compute the subsumption hierarchy of the ontologies whose concepts are used in the OWLS Profile descriptions as input and output concepts. The concept ranking algorithm is applied over this hierarchy in order to determine similar concepts based on different degrees of semantic matching relaxation, such as subclass or sibling hierarchical relationships. The domain independent planning system's role is to semantically search the space of possible compositions of Web services, generating plans according to the desirable level of relaxation.