Marc Gyssens

Marc Gyssens
Hasselt University · Faculty of Sciences

PhD Mathematics (specialization Computer Science)

About

162
Publications
9,295
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
3,470
Citations

Publications

Publications (162)
Article
Full-text available
We show that the matrix query language MATLANG corresponds to a natural fragment of the positive relational algebra on K-relations. The fragment is defined by introducing a composition operator and restricting K-relation arities to 2. We then proceed to show that MATLANG can express all matrix queries expressible in the positive relational algebra...
Article
Fragments of Tarski's relation algebra form the basis of many versatile graph and tree query languages including the regular path queries, XPath, and SPARQL. Surprisingly, however, a systematic study of the relative expressive power of relation algebra fragments on trees has not yet been undertaken. In this work, we perform such a systematic study....
Article
Many graph query languages rely on composition to navigate graphs and select nodes of interest, even though evaluating compositions of relations can be costly. Often, this need for composition can be reduced by rewriting toward queries using semi-joins instead, resulting in a significant reduction of the query evaluation cost. We study techniques t...
Chapter
We show that the matrix query language corresponds to a natural fragment of the positive relational algebra on K-relations. The fragment is defined by introducing a composition operator and restricting K-relation arities to two. We then proceed to show that can express all matrix queries expressible in the positive relational algebra on K-relations...
Article
Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries are built from the identity relation and edge relations using composition and union. We study the effects on relative expressiveness when we add transitive closure, proje...
Article
Full-text available
Many data sources can be represented easily by collections of sets of objects. For several practical queries on such collections of sets of objects, the answer does not depend on the precise composition of these sets, but only on the number of sets to which each object belongs. This is the case k= 1 for the more general situation where the query an...
Preprint
We show that the matrix query language $\mathsf{MATLANG}$ corresponds to a natural fragment of the positive relational algebra on $K$-relations. The fragment is defined by introducing a composition operator and restricting $K$-relation arities to two. We then proceed to show that $\mathsf{MATLANG}$ can express all matrix queries expressible in the...
Article
Symmetric queries are introduced as queries on a sequence of sets of objects the result of which does not depend on the order of the sets. An appropriate data model is proposed, and two query languages are introduced, QuineCALC and SyCALC. They are correlated with the symmetric Boolean respectively relational functions. The former correlation yield...
Chapter
For several practical queries on bags of sets of objects, the answer does not depend on the precise composition of these sets, but only on the number of sets to which each object belongs. This is the case k = 1 for the more general situation where the query answer only depends on the number of sets to which each group of at most k objects belongs....
Chapter
Fragments of Tarski’s relation algebra form the basis of many versatile graph and tree query languages including the regular path queries, XPath, and SPARQL. Surprisingly, however, a systematic study of the relative expressive power of relation algebra fragments on trees has not yet been undertaken. Our approach is to start from a basic fragment wh...
Article
Full-text available
Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries are built from the identity relation and edge relations using composition and union. We study the effects on relative expressiveness when we add transitive closure, proje...
Conference Paper
Many graph query languages rely on the composition operator to navigate graphs and select nodes of interests, even though evaluating compositions of relations can be costly. Often, this need for composition can be reduced by rewriting towards queries that use semi-joins instead. In this way, the cost of evaluating queries can be significantly reduc...
Conference Paper
Motivated by the continuing interest in the tree data model, we study the expressive power of downward fragments of navigational query languages on trees. The basic navigational query language we consider expresses queries by building binary relations from the edge relations and the identity relation, using composition and union. We study the effec...
Article
Akhtar et al. introduced equality-generating constraints and functional constraints as a first step towards dependency-like integrity constraints for RDF data [3]. Here, we focus on functional constraints. Since the usefulness of functional constraints is not limited to the RDF data model, we study the functional constraints in the more general set...
Article
Given a document D in the form of an unordered node-labeled tree, we study the expressiveness on D of various basic fragments of XPath, the core navigational language on XML documents. Working from the perspective of these languages as fragments of Tarski's relation algebra, we give characterizations, in terms of the structure of D, for when a bina...
Article
Full-text available
Motivated by both established and new applications, we study navigational query languages for graphs (binary relations). The simplest language has only the two operators union and composition, together with the identity relation. We make more powerful languages by adding any of the following operators: intersection; set difference; projection; copr...
Article
Conditional independence (CI) statements occur in several areas of computer science and artificial intelligence, e.g., as embedded multivalued dependencies in database theory, disjunctive association rules in data mining, and probabilistic CI statements in probability theory. Although, syntactically, such constraints can always be represented in th...
Conference Paper
Akhtar et al. introduced equality-generating constraints and functional constraints as an initial step towards dependency-like integrity constraints for RDF data [1]. Here, we focus on functional constraints. The usefulness of functional constraints is not limited to the RDF data model. Therefore, we study the functional constraints in the more gen...
Article
Full-text available
Many data-intensive applications have to query a database that involves sequences of sets of objects. It is not uncommon that the order of the sets in such a sequence does not affect the result of the query. Such queries are called symmetric. In this paper, the authors wish to initiate research on symmetric queries. Thereto, a data model is propose...
Article
Full-text available
Motivated by applications in databases, this paper considers various fragments of the calculus of binary relations. The fragments are obtained by leaving out, or keeping in, some of the standard operators, along with some derived operators such as set difference, projection, coprojection, and residuation. For each considered fragment, a characteriz...
Article
Several established and novel applications motivate us to study the expressive power of navigational query languages on graphs, which represent binary relations. Our basic language has only the operators union and composition, together with the identity relation. Richer languages can be obtained by adding other features such as other set operators,...
Article
Full-text available
We study the expressiveness of a positive fragment of path queries, denoted Path+, on documents that can be represented as node-labeled trees. The expressiveness of Path+ is studied from two angles. First, we establish that Path+ is equivalent in expressive power to two particular subfragments, as well as to the class of tree queries, a subclass of...
Conference Paper
Motivated by both established and new applications, we study navigational query languages for graphs (binary relations). The simplest language has only the two operators union and composition, together with the identity relation. We make more powerful languages by adding any of the following operators: intersection; set difference; projection; copr...
Article
The logical and algorithmic properties of stable conditional independence (CI) as an alternative structural representation of conditional independence information are investigated. We utilize recent results concerning a complete axiomatization of stable conditional independence relative to discrete probability measures to derive perfect model prope...
Article
Full-text available
Conference Paper
Full-text available
We study deterministic regular expressions extended with the counting operator. There exist two notions of determinism, strong and weak determinism, which almost coincide for standard regular expressions. This, however, changes dramatically in the presence of counting. In particular, we show that weakly deterministic expressions with counting are e...
Conference Paper
Full-text available
We study the expressiveness of a positive fragment of path queries, denoted Path+, on node-labeled trees documents. The expres- siveness of Path+ is studied from two angles. First, we establish that Path+ is equivalent in expressive power to a particular sub-fragment as well as to the class of tree queries, a sub-class of the flrst-order conjunc- t...
Article
Full-text available
We give a language-independent characterization of the expressive power of the relational algebra on finite sets of source-target relation instance pairs. The associated decision problem is shown to be co-graph-isomorphism hard and in co NP. The main result is also applied in providing a new characterization of the generic relational queries.
Article
Full-text available
Article
Full-text available
Recent studies have proposed structural summary techniques for path-query evaluation on semi-structured data sources. One major line of this research has been the introduction of the DataGuide, 1-index, 2-index, and A(k) indices, and subsequent investigations and generalizations. Another recent study has considered structural characterizations of f...
Conference Paper
Full-text available
A lattice-theoretic framework is introduced that permits the study of the conditional in- dependence (CI) implication problem relative to the class of discrete probability measures. Semi-lattices are associated with CI state- ments and a finite, sound and complete in- ference system relative to semi-lattice inclu- sions is presented. This system is...
Article
In this paper we derive a generic form of structural decomposition for the constraint satisfaction problem, which we call a guarded decomposition. We show that many existing decomposition methods can be characterised in terms of finding guarded decompositions satisfying certain specified additional conditions.Using the guarded decomposition framewo...
Article
Typechecking consists of statically verifying whether the output of an XML transformation always conforms to an output type for documents satisfying a given input type. In this general setting, both the input and output schema as well as the transformation are part of the input for the problem. However, scenarios where the input or output schema ca...
Article
We study the implication problem of measure-based constraints. These constraints are formulated in a framework for measures generalizing that for mathematical measures. Measures arise naturally in a wide variety of domains. We show that measure constraints, for particular measures, correspond to constraints that occur in relational databases, data...
Article
Full-text available
This paper is concerned with the learning process of a sparse interaction network, for example, a gene-protein interaction network. The advantage of the process we purpose is that there will always be a student S that fits the teacher T very well with a relatively small data set and a high number of unknown components, i.e., when the number of meas...
Article
A lattice-theoretic framework is introduced that permits the study of the conditional independence (CI) implication problem relative to the class of discrete probability measures. Semi-lattices are associated with CI statements and a finite, sound and complete inference system relative to semi-lattice inclusions is presented. This system is shown t...
Conference Paper
Full-text available
Supporting efficient access to XML data using XPath [3] continues to be an important research problem [6, 12]. XPath queries Supporting efficient access to XML data using XPath [3] continues to be an important research problem [6, 12]. XPath queries are used to specify nodelabeled trees which match portions of the hierarchical XML data. In XPath qu...
Conference Paper
Full-text available
In this paper [1] we study the identification of sparse interaction networks, from a given set of observations, as a machine learning problem. An example of such a network is a sparse gene-protein interaction network, for more details see [2]. Sparsity means that we are provided with a small data set and a high number of unknown components of the s...
Chapter
Full-text available
In this study we will focus on piecewise linear state space models for gene-protein interaction networks. We will follow the dynamical systems approach with special interest for partitioned state spaces. From the observation that the dynamics in natural systems tends to punctuated equilibria, we will focus on piecewise linear models and sparse and...
Article
Full-text available
In this paper we study the potential of gene-protein interaction networks to store input-output patterns. The central question in this study concerns the memory capacity of a network of a given number of genes and proteins, which interact according to a linear state space model with external inputs. Here it is assumed that to a certain combination...
Conference Paper
Full-text available
Recent studies have proposed structural summary techniques for path- query evaluation on semi-structured data sources. One major line of this research has been the introduction of the DataGuide, 1-index, 2-index, and A(k) indices, and subsequent investigations and generalizations. Another recent study has con- sidered structural characterizations o...
Conference Paper
We introduce a new methodology for coupling language-induced partitions and index-induced partitions on XML documents that is aimed for the benefit of efficient evaluation of XPath queries. In particular, we identify XPath fragments which are ideally coupled with the newly introduced P(k)-partition which has its definition grounded in the well-know...
Article
Full-text available
Recent studies have proposed structural summary tech-niques for path query evaluation on semi-structured data sources. One major line of this research has been the intro-duction of the DataGuide, 1-index, 2-index, and A(k) in-dices, and subsequent investigations and generalizations. Another recent study has considered structural characteri-zations...
Conference Paper
Full-text available
Given a document D in the form of an unordered labeled tree, we study the expressibility on D of various fragments of XPath, the core navigational language on XML documents. We give charac- terizations, in terms of the structure of D, for when a binary relation on its nodes is definable by an XPath expression in these fragm ents. Since each pair of...
Chapter
Languages for models of nested relations and complex objects have been attracting considerable attention recently. Some of these languages are algebraic, others are calculus based, some are logic programming oriented. This paper describes these languages and surveys recent results about the expressive power of these languages. The emphasis is on co...
Article
In this talk (draft paper) we develop the theory of structural decompositions for the CSP. We begin with the very general notion of a guarded decomposition and make several simplifying assumptions to arrive a the definition of an acyclic guarded cover. We show how many existing decompositions can seen as acyclic guarded covers. We develop a generic...
Conference Paper
Full-text available
In this paper we introduce a generic form of struc- tural decomposition for the constraint satisfaction problem, which we call a guarded decomposi- tion. We show that many existing decomposition methods can be characterized in terms of finding guarded decompositions satisfying certain speci- fied additional conditions. Using the guarded decompositi...
Article
Full-text available
Article
We extend Chandra and Harel's seminal work on computable queries for relational databases to a setting in which also spatial data may be present, using a constraint-based data model. Concretely, we introduce both coordinate-based and point-based query languages that are complete in the sense that they can express precisely all computable queries th...
Article
Full-text available
Object-oriented applications of database systems require database transformations involoving nonstandard functionalities such as set manipulation and object creation, that is, the introduction of new domain elements. To deal with thse functionalities, Abiteboul and Kanellakis [1989] introduced the “determinate” transformations as a generalization o...
Conference Paper
Full-text available
. Recently, Abiteboul and Kanellakis introduced the notion of determinate query to describe database queries having the ability to create new domain elements. As there are no natural determinate-complete query languages known, more restrictive (the constructive queries) and more general (the semi-deterministic queries) notions of query were conside...
Article
Full-text available
The linear database model, in which semi-linear sets are the only geometric objects, has been identified as suitable for spatial database applications from both modeling expressiveness as query efficiency considerations. For querying linear databases, the language has been proposed. In this paper, we examine the expressiveness of this language. Fir...
Article
Full-text available
We investigate the expressive limitations of FO+ poly extended with a connectivity predicate, Conn. Etc., etc., etc... 1 Introduction Blah, blah, blah. 2 Preliminaries First some basics from first-order logic. A signature, OmegaGamma is a collection of relation symbols, function symbols, and constant symbols. Let L(OmegaGamma denote the set of all...
Article
The nested model is an extension of the traditional, “flat” relational model in which relations can also have relation-valued entries. Its “default” query language, the nested algebra, is rather weak, unfortunately, since it is only a conservative extension of the traditional, flat relational algebra, and thus can express only a small fraction of t...
Article
Full-text available
A set of 614.22h observing hours covering the activity of the Leonid meteor shower as logged by 230 observers was used to determine the population index and activity profiles of the 2000 Leonids. Three clear maxima in terms of Zenithal Hourly Rates (ZHR) are found. The first peak at lambda=235+-0.01 (November 17, 8h07m UT) falls about 15 minutes af...
Article
Full-text available
The nested model is an extension of the traditional, "flat" relational model in which relations can also have relationvalued entries. Its "default" query language, the nested algebra, is rather weak, unfortunately, since it is only a conservative extension of the traditional, "flat" relational algebra, and thus can only express a small fraction of...
Conference Paper
)St'ephane Grumbach1and Jianwen Su2and Christophe Tollu31University of Toronto and INRIAx2University of California at Santa Barbara--3Universit'e Paris-Nord, VilletaneusekAbstract. We give an AC0upper bound on the complexity of first-oderqueries over (infinite) databases defined by restricted linear constraints.This result enables us to deduce the...
Article
Full-text available
An overall activity profile of the 1999 Leonid meteor shower is presented based on the observations of 434 observers who reported 277172 Leonids in 10806 observing periods. A storm of Leonid activity was observed from western Asian, European, and African locations at a solar longitude of lambda=235.285+-0.001, corresponding to November 18, 1999, 2h...
Article
Several authors have suggested using first-order logic over the real numbers to describe spatial database applications. Geometric objects are then described by polynomial inequalities with integer coefficients involving the coordinates of the objects. Such geometric objects are called semialgebraic sets. Similarly, queries are expressed by polynomi...
Article
Full-text available
Some constraint languages are more powerful than others because they allow us to express a larger collection of problems. In this paper, we give a precise meaning to this concept of expressive power for constraints over finite sets of values. The central result of the paper is that the expressive power of a given set of constraint types is determin...
Conference Paper
We exhibit a coordinate-based language, called PFOL, which is sound for the linear queries computable in first-order logic over the reals and extends the latter's restriction to linear arithmetic. To evaluate its expressive power, we first consider PFOL-finite, the PFOL programs that compute finite outputs upon finite inputs. In order to study this...
Article
Full-text available
We present a multi-dimensional database model, which we believe can serve as a conceptual model for On-Line Analytical Processing (OLAP)-based applications. Apart from providing the functionalities necessary for OLAP-based applications, the main feature of the model we propose is a clear separation between structural aspects and the contents. This...
Article
There is a very close relationship between constraint satisfaction problems and the satisfaction of join-dependencies in a relational database which is due to a common underlying structure, namely a hypergraph. By making that relationship explicit we are able to adapt techniques previously developed for the study of relational databases to obtain n...
Article
Full-text available
Many combinatorial search problems can be expressed as `constraint satisfaction problems', and this class of problems is known to be NP-complete in general. In this paper we investigate the subclasses which arise from restricting the possible constraint types. We first show that any set of constraints which does not give rise to an NP-complete clas...
Article
. In this paper we investigate which constraints may be derived from a given set of constraints. We show that, given a set of relations R, all of which are invariant under some set of permutations P , it is possible to derive any other relation which is invariant under P , using only the projection, Cartesian product, and selection operators, toget...
Conference Paper
Full-text available
We introduce query languages for spatial databases that are complete, in the sense that they can express precisely all computable queries that are generic with respect to cer- tain classes of transformation8 of space, corresponding to certain geometric interpretations of spatial data. We thus extend Chandra and Hare& seminal work on computable quer...
Conference Paper
Full-text available
Several authors have suggested to use first-order logic over the real numbers to describe spatial database applications. Geometric objects are then described by polynomial inequalities with integer coefficients involving the coordinates of the objects. Such geometric objects are called semi-algebraic sets. Similarly, queries are expressed by polyno...
Conference Paper
Full-text available
It has been argued that the linear database model, in which semi-linear sets are the only geometric objects, is very suitable for most spatial database applications. For querying linear databases, the language FO + linear has been proposed. We present both negative and positive results regarding the expressiveness of FO+linear. First, we show that...
Article
While the relational data model and many of its extensions have proven to be of considerable importance to many database applications, it has become clear that some advanced systems require more flexible structures and query languages. The expression of queries based on the occurrence of substructures on instance level (i.e., pattern matchings) req...
Conference Paper
Full-text available
We investigate which constraints may be derived from a given set of constraints. We show that, given a set of relations ℛ, all of which are invariant under some set of permutations P, it is possible to derive any other relation which is invariant under P, using only the projection, Cartesian product, and selection operators, together with the effec...
Conference Paper
Full-text available
)Marc GyssensyUniversity of LimburgLaks V.S. LakshmananzConcordia UniversityIyer N. SubramanianzConcordia UniversityAbstractTables are one of the most natural representations of real-lifedata. Previous table-based data models (such as relational,nested relational, and complex objects models) capture onlya limited variety of real-life tables. In thi...

Network

Cited By