Ioannis Pachoulakis

A Survey on Models and Query Languages for Temporally Annotated RDF

In this paper, we provide a survey on the models and query languages for temporally annotated RDF. In most of the works, a temporally annotated RDF ontology is essentially a set of RDF triples associated with temporal constraints, where, in the simplest case, a temporal constraint is a validity temporal interval. However, a temporally annotated RDF ontology may also be a set of triples connecting resources with a specific lifespan, where each of these triples is also associated with a validity temporal interval. Further, a temporal RDF ontology may be a set of triples connecting resources as they stand at specific time points. Several query languages for temporally annotated RDF have been proposed, where most of which extend SPARQL or translate to SPARQL. Some of the works provide experimental results while the rest are purely theoretical.

Temporally Annotated Extended Logic Programs

Extended logic programs (ELPs) are a set of logic rules with strong negation allowed in the bodies or head of the rules and weak negation ~ allowed in the bodies of the rules. ELPs enable for various forms of reasoning that cannot be achieved by definite logic programs. Answer Set Programming provides a widely acceptable semantics for ELPs. However, ELPs do not provide information regarding the temporal intervals that derived ELP literals or weakly negated ELP literals are valid. In this paper, we associate ELP rules with their validity temporal interval, resulting in a temporally annotated logic program. A ground temporal literal has the form L:i, where L is a ground ELP literal or weakly negated ELP literal and i is a temporal interval. We define (simple) entailment and maximal entailment of a ground temporal literal L:i from a temporally annotated logic program C. Both kinds of entailment are based on Answer Set Programming. Additionally, we provide an algorithm that for an ELP literal or a weakly negated ELP literal L returns a list with all temporal intervals i such that a temporally annotated logic program C maximally entails L:i. Based on this algorithm, the answer of various kinds of temporal queries can be provided.

Exergames for Parkinson's Disease patients: The balloon goon game

Parkinsons Disease patients attending traditional long-term rehabilitation programs may lose interest and eventually drop out, as a direct result of the repeatability of the prescribed exercises. Technology-supported opportunities in the form of character-based, virtual reality exercise games (called “exergames”) can engage players to train in a non-linear fashion by providing an experience which varies from one game loop the next. The present work reports on a Kinect-based Unity3D exergame tailored to PD patients with mild to moderate symptoms which can be used in both clinical and home settings. The game supports a collection of gestures drawn from existing PD-specific training programs which advocate big and purposeful movements, intended to improve postural stability and reflexes as well as increase the overall mobility of upper and lower limbs. When a patients movements “match” a programmed gesture, a 3D cartoon avatar responds accordingly. Finally, in-game decision-making purports to improve the patients cognitive reaction.

Building a gait analysis framework for Parkinson's disease patients: Motion capture and skeleton 3D representation

Stereoscopic vision has been very successful in recording and analyzing human motion. Using stereoscopic vision techniques and motion tracking of selected body joints, we have extracted and processed skeletal data to measure gait-related parameters and metrics of people with specific kinetic deficiencies. We have focused on Parkinsons Disease (PD) patients and have secured accurate representations of the kinesiological state of a patient at a given point in time (a kinesiological “imprint”). This stored imprint, for a given recording session, consists of a 3D skeletal visualization and associated derived gait metrics such as walking speed and stride length. In due time, a time sequence of accurate kinesiological imprints for any given patient will provide attending neurologists with evolutionary data of sufficient accuracy and granularity to better assess disease progress as well as quantify that patients response to specific medications.

A framework for modular ERDF ontologies

The success of the Semantic Web is impossible without any form of modularity, encapsulation, and access control. In an earlier paper, we extended RDF graphs with weak and strong negation, as well as derivation rules. The ERDF #n-stable model semantics of the extended RDF framework (ERDF) is defined, extending RDF(S) semantics. In this paper, we propose a framework for modular ERDF ontologies, called modular ERDF framework, which enables collaborative reasoning over a set of ERDF ontologies, while support for hidden knowledge is also provided. In particular, the modular ERDF stable model semantics of modular ERDF ontologies is defined, extending the ERDF #n-stable model semantics. Our proposed framework supports local semantics and different points of view, local closed-world and open-world assumptions, and scoped negation-as-failure. Several complexity results are provided.

A Kinect-Based Physiotherapy and Assessment Platform for Parkinson's Disease Patients.

We report on a Kinect-based, augmented reality, real-time physiotherapy platform tailored to Parkinsons disease (PD) patients. The platform employs a Kinect sensor to extract real-time 3D skeletal data (joint information) from a patient facing the sensor (at 30 frames per second). In addition, a small collection of exercises practiced in traditional physiotherapy for PD patients has been implemented in the Unity 3D game engine. Each exercise employs linear or circular movement patterns and poses very light-weight processing demands on real-time computations. During an exercise, trainer instruction demonstrates correct execution and Kinect-provided 3D joint data are fed to the game engine and compared to exercise-specific control routines to assess proper posture and body control in real time. When an exercise is complete, performance metrics appropriate for that exercise are computed and displayed on screen to enable the attending physiotherapist to fine-tune the exercise to the abilities/needs of an individual patient as well as to provide performance feedback to the patient. The platform can operate in a physiotherapists office and, following appropriate validation, in a home environment. Finally, exercises can be parameterized meaningfully, depending on the intended purpose (motor assessment versus plain exercise at home).

Why-provenance information for RDF, rules, and negation

The provenance (i.e., origins) of derived information on the Web is crucial in many applications to allow information quality assessment, trust judgments, accountability, as well as understanding the temporal and spatial status of the information. On the other hand, the inclusion of negative information in knowledge representation both in the form of negation-as-failure and explicit negation is also important to allow various forms of reasoning, provided that weakly negated information is associated with the sources (contexts) in which it holds. In this work, we consider collections of g-RDF ontologies, distributed over the web, along with a set of conflict statements expressing that information within a pair of g-RDF ontologies cannot be combined together for deriving new information. A g-RDF ontology is the combination of (i) a g-RDF graph G (i.e., a set of positive and strongly negated RDF triples, called g-RDF triples) and (ii) a g-RDF program P containing derivation rules with possibly both explicit and scoped weak negation. Information can be inferred through the g-RDF graphs or the derivation rules of the g-RDF ontologies, or through the RDFS derivation rules. We associate each derived grounded g-RDF triple [¬] p(s, o) with the set of names S of the g-RDF ontologies that contributed to its derivation. To achieve this, we define the provenance stable models of a g-RDF ontology collection. We show that our provenance g-RDF semantics faithfully extends RDFS semantics. Finally, we provide an algorithm based on Answer Set Programming that computes all provenance stable models of a g-RDF ontology collection and provides the answer to various kinds of queries. Various complexity results are provided.

Provenance and Temporally Annotated Logic Programming

In this paper, we consider provenance and temporally annotated logic rules (pt-logic rules, for short), which are definite logic programming rules associated with the name of the source that they originate and the temporal interval during which they are valid. A collection of pt-logic rules form a provenance and temporally annotated logic program P, called pt-logic program, for short. We develop a model theory for P and define its maximally temporal entailments of the form A: , indicating that atom A is derived from a set of sources S and holds at a maximal temporal interval ti, according to S. We define a consequence operator that derives exactly the maximally temporal entailments of P for a set of sources. We show that the complexity of the considered entailment is EXPTIME-complete.

3D reconstruction and visualization of astrophysical wind volumes using physical models

This article reports on the application of a framework used to model, simulate and visualize the 3D structure of astrophysical wind volumes. The modeling methodology is similar to multidirectional medical tomography in that the spatial structure of an extended target can be reconstructed from a sequence of images obtained by scanning that target from several directions. Even though the controlled environment realized in diagnostic radiology cannot be replicated in the study of astrophysical phenomena, strong candidates for astrophysical tomography do exist in hot, close double stars locked in orbits around a common center of mass. As the Keplerian orbit is traced out, the geometry presented to the observer varies so that each star constitutes an analyzer upon its companions wind and probes its structure. Since these targets are too far to be resolved spatially, we study and model the UV spectral lines of prominent wind ions, which scatter photospheric UV light so that line shapes vary as the stars revolve and as inhomogeneities form, propagate, and evolve in the composite wind. The framework presented is applied to two hot close binaries near the applicability limits of the discussed methodology. Two novel custom-made tools that aid the analysis of the spectra and the visualization of the results are also presented. The first of these, the Spectrum Analyzer and Animator, automates the derivation of light curves from the observed spectra and the generation of synthetic binary wind-line profiles, which reproduce the morphologies and variabilities of the observed wind profiles. After the composite wind structure of a binary has been recovered, the second tool, the Binary 3D Renderer —also authored in IDL—aids the visualization of the results by simulating the motion of the system (stars, winds and wind-interaction effects) around the binarys center of mass. The Binary 3D Renderer thus repackages the end product of a lengthy physical modeling process to generate physically sound, realistic multimedia content and increase the effectiveness and communication impact of the research results.

Faceted operations on composed RDF ontologies

Public and private organisations increasingly release their data. The use of these open data can be supported and stimulated by providing considerable metadata, including discovery, contextual and other detailed metadata. This paper argues that faceted indexing of the RDF ontologies, published as linked open data LOD, is an important part of their associated metadata. On the other hand, information needs to be composed from multiple sources to create new information. Through primitive faceted formulas using faceted indexing terms and a list of validity time intervals, we are able to take the union of all RDF ontologies indexed by these terms and are valid in all provided validity time intervals. The resulted RDF ontology is indexed by the provided index terms and has a list of validity time intervals derived by the validity time intervals of the unioned RDF ontologies. By combining both union and intersection operators on primitive faceted formulas, complex expressions can be formed that return a composed RDF ontology, its faceted indexing and validity time intervals. All algorithms are provided along with their complexity.