Theofilos P. Mailis

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Fuzzy Description Logics (fuzzy DLs) are extensions of classic DLs that are capable of representing and reasoning with imprecise and vague knowledge. Though reasoning algorithms for very expressive fuzzy DLs have been developed and optimizations have started to be explored, the efficiency of such systems is still questionable, and the study of tractable(More)
Extracting and validating emotional cues through analysis of users' facial expressions is of high importance for improving the level of interaction in man machine communication systems. Extraction of appropriate facial features and consequent recognition of the user's emotional state that can be robust to facial expression variations among different users(More)
This paper proposes a number of content-based image classification techniques based on fusing various low-level MPEG-7 visual descriptors. The goal is to fuse several descriptors in order to improve the performance of several machine-learning classifiers. Fusion is necessary as descriptors would be otherwise incompatible and inappropriate to directly(More)
Sophisticated uncertainty representation and reasoning are necessary for the alignment and integration of Web data from different sources. For this purpose the extension of the Description Logics using fuzzy set theory has been proposed, resulting to fuzzy Description Logics (DLs). However, despite the fact that since the initial proposal a lot of work has(More)
In this paper, we describe fuzzy CARIN, a knowledge representation language combining fuzzy Description Logics with Horn rules. Fuzzy CARIN integrates the management of fuzzy logic into the non-recursive CARIN language. We introduce the decision problems of answering to conjunctive queries, unions of conjunctive queries and the existential entailment(More)
Fuzzy Description Logics (DLs) provide a means for representing vague knowledge about an application domain. In this paper, we study fuzzy extensions of conjunctive queries (CQs) over the DL $${\mathcal {SROIQ}}$$ SROIQ based on finite chains of degrees of truth. To answer such queries, we extend a well-known technique that reduces the fuzzy ontology to a(More)
Fuzzy Description Logics (DLs) generalize crisp ones by providing membership degree semantics for concepts and roles. A popular technique for reasoning in fuzzy DL ontologies is by providing a reduction to crisp DLs and then employ reasoning in the crisp DL. In this paper we adopt this approach to solve conjunctive query (CQ) answering problems for fuzzy(More)
Fuzzy Description Logics (f-DLs) are extensions of classic DLs that are capable of representing and reasoning about imprecise and vague knowledge. Though reasoning algorithms for very expressive fuzzy DLs have been explored, an open issue in the fuzzy DL community is the study of tractable systems. In this paper we introduce the fuzzy extension of EL, we(More)
In the database community Polystores is an emerging and promising approach for data federation that aims at designing a unified querying layer over multiple data models. In the Semantic Web community a similar in spirit approach of Ontology-Based Data Access (OBDA) has been recently proposed, attracted a lot of attention, and proved its success in several(More)