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Bart Kuijpers

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Sebastian Rudolph

Karlsruhe Institute of Technology (KIT)

Marialba Pastor

UNAM

Diego Calvanese

Free University of Bozen-Bolzano

University of Warsaw

Rice University

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Papers by Bart Kuijpers

Decidable containment of recursive queries

Theoretical Computer Science, 2005

One of the most important reasoning tasks on queries is checking containment, i.e., verifying whe... more One of the most important reasoning tasks on queries is checking containment, i.e., verifying whether one query yields necessarily a subset of the result of another one. Query containment is crucial in several contexts, such as query optimization, query reformulation, knowledge-base verification, information integration, integrity checking, and cooperative answering. Containment is undecidable in general for Datalog, the fundamental language for expressing recursive queries. On the other hand, it is known that containment between monadic Datalog queries and between Datalog queries and unions of conjunctive queries are decidable. It is also known that containment between unions of conjunctive two-way regular path queries, which are queries used in the context of semistructured data models containing a limited form of recursion in the form of transitive closure, is decidable. In this paper, we combine the automata-theoretic techniques at the base of these two decidability results to show that containment of Datalog in union of conjunctive two-way regular path queries is decidable in 2EXPTIME. By sharpening a known lower bound result for containment of Datalog in union of conjunctive queries we show also a matching lower bound.

First-order complete and computationally complete query languages for spatio-temporal databases

ACM Transactions on Computational Logic, 2008

We address a fundamental question concerning spatio-temporal database systems: “What are exactly ... more We address a fundamental question concerning spatio-temporal database systems: “What are exactly spatio-temporal queries?” We define spatio-temporal queries to be computable mappings that are also generic , meaning that the result of a query may only depend to a limited extent on the actual internal representation of the spatio-temporal data. Genericity is defined as invariance under groups of geometric transformations that preserve certain characteristics of spatio-temporal data (e.g., collinearity, distance, velocity, acceleration, …). These groups depend on the notions that are relevant in particular spatio-temporal database applications. These transformations also have the distinctive property that they respect the monotone and unidirectional nature of time. We investigate different genericity classes with respect to the constraint database model for spatio-temporal databases and we identify sound and complete languages for the first-order and the computable queries in these gen...

Deciding Termination of Query Evaluation in Transitive-Closure Logics for Constraint Databases

Lecture Notes in Computer Science, 2002

We study extensions of first-order logic over the reals with different types of transitive-closur... more We study extensions of first-order logic over the reals with different types of transitive-closure operators as query languages for constraint databases that can be described by Boolean combinations of polynomial inequalities over the reals. We are in particular interested in deciding the termination of the evaluation of queries expressible in these transitive-closure logics. It turns out that termination is undecidable in general. However, we show that the termination of the transitive closure of a continuous function graph in the two-dimensional plane, viewed as a binary relation over the reals, is decidable, and even expressible in first-order logic over the reals. Based on this result, we identify a particular transitive-closure logic for which termination of query evaluation is decidable and which is more expressive than first-order logic over the reals. Furthermore, we can define a guarded fragment in which exactly the terminating queries of this language are expressible.

Constraint databases, geometric elimination and geographic information systems

From 20.05. to 25.05., the Dagstuhl Seminar 07212 Constraint Databases, Geometric Elimination and... more From 20.05. to 25.05., the Dagstuhl Seminar 07212 Constraint Databases, Geometric Elimination and Geographic Information Systems was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The rst section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.

Floris Geerts, University of Limburg Bart Kuijpers, University of Antwerp

Research Issues in Structured and Semistructured Database Programming, 2000

We consider two-dimensional spatial databases defined in terms of polynomial inequalities and foc... more We consider two-dimensional spatial databases defined in terms of polynomial inequalities and focus on the potential of program-ming languages for such databases to express queries related to topo-logical connectivity. It is known that the topological connectivity test is not first-order expressible. One approach to obtain a language in which connectivity queries can be expressed would be to extend FO+ Poly with a generalized (or Lindström) quantifier expressing that two points belong to the same connected component of a given database. ...

Program Chairs of SSTDM-12 Workshop

With advances in remote sensors, sensor networks, and proliferation of location sensing devices i... more With advances in remote sensors, sensor networks, and proliferation of location sensing devices into common walks of lives and businesses, the generation of disparate, dynamic, and geographically distributed spatiotemporal data has exploded in recent years. Knowledge extracted from spatial and spatiotemporal data plays a critical role in our daily lives, whether it is to understand the human implications of global environmental changes, responding to natural disasters, or simply finding alternate routes in case of an emergency ...

Checking the Integrity of Spatial Integrity Constraints

Integrity constraints play a major role when the quality of spatial data is checked by automatic ... more Integrity constraints play a major role when the quality of spatial data is checked by automatic procedures. Nevertheless the possibilities of checking the internal consistency of the integrity constraints themselves are hardly researched jet. This work analyses the applicability of reasoning techniques like the composition of spatial relations and constraint satisfaction in networks of constraints to find conflicts and redundancies in sets of spatial semantic integrity constraints. These integrity rules specify relations among entity classes. Such relations must hold to assure that the data is fitting to the semantics intended by the data model. For spatial data many semantic integrity constraints are based on spatial properties described for example through qualitative topological or metric relations. Since integrity constraints are defined at the class level, the reasoning properties of these spatial relations can not directly be applied. Therefore a set of class relations has be...

Semantic Trajectory Data Mining: a User Driven Approach

Trajectories left behind cars, humans, birds or any other moving object are a new kind of data wh... more Trajectories left behind cars, humans, birds or any other moving object are a new kind of data which can be very useful in decision making process in several application domains. These data, however, are normally available as sample points, and therefore have very little or no semantics. The analysis and knowledge extraction from trajectory sample points is very difficult from the user's point of view, and there is an emerging need for new data models, manipulation techniques, and tools to extract meaningful patterns from these data. In this paper we propose a new methodology for knowledge discovery from trajectories. We propose through a semantic trajectory data mining query language several functionalities to select, preprocess, and transform trajectory sample points into semantic trajectories at higher abstraction levels, in order to allow the user to extract meaningful, understandable, and useful patterns from trajectories. We claim that meaningful patterns can only be extra...

Temporal Support of Regular Expressions in Sequential Pattern Mining

Classic algorithms for sequential pattern discovery,return all frequent sequences present in a da... more Classic algorithms for sequential pattern discovery,return all frequent sequences present in a database. Since, in general, only a few ones are interesting from a user's point of view, languages based on regular expressions (RE) have been proposed to restrict frequent sequences to the ones that satisfy user-specified constraints. Although the support of a sequence is computed as the number of data-sequences satisfying a pattern with respect to the total number of data-sequences in the database, once regular expressions come into play, new approaches to the concept of support are needed. For example, users may be interested in computing the support of the RE as a whole, in addition to the one of a particular pattern. As a simple example, the expression $(A|B).C$ is satisfied by sequences like A.C or B.C. Even though the semantics of this RE suggests that both of them are equally interesting to the user, if neither of them verifies a minimum support although together they do), the...

An analytic solution to the alibi query in the bead model for moving object data

Moving objects produce trajectories, which are stored in databases by means of finite samples of ... more Moving objects produce trajectories, which are stored in databases by means of finite samples of time-stamped locations. When also speed limitations in these sample points are known, beads can be used to model the uncertainty about the object's location in between sample points. In this setting, a query of particular interest, that has been studied in the literature of geographic information systems (GIS), is the alibi query. This boolean query asks whether two moving objects can have physically met. This adds up to deciding whether the necklaces of beads of these objects intersect. This problem can be reduced to deciding whether two beads intersect. Since, existing software to solve this problem fails to answer this question within a reasonable time, we propose an analytical solution to the alibi query, which can be used to answer the alibi query in constant time, a matter of milliseconds or less, for two single beads and in time proportional to the product of their lengths for...

Propagating and measuring anchor uncertainty in space-time prisms on road networks

Space-time prisms capture all possible spatio-temporal locations of a moving object between sampl... more Space-time prisms capture all possible spatio-temporal locations of a moving object between sample points given speed limit constraints on its movement. These sample points are usually considered to be perfect measurements. In this paper we restrict ourselves to a road network and extend the notion of sample points to sample regions, which are bounded, sometimes disconnected, subsets of space-time wherein each point is a possible location, with its respective probability, where a moving object could have originated from or arrived in. This model allows us to model measurement errors, multiple possible simultaneous locations and even flexibility of a moving object. We develop an algorithm that computes the envelope of all space-time prisms that have an anchor in these sample regions and we developed an algorithm that computes for any spatio-temporal point the probability with which a space-time prism, with anchors in these sample regions, contains that point. We implemented these alg...

07212 Abstracts Collection – Constraint Databases, Geometric Elimination ang Geographic Information Systems

From 20.05. to 25.05., the Dagstuhl Seminar 07212 ``Constraint Databases, Geometric Elimination a... more From 20.05. to 25.05., the Dagstuhl Seminar 07212 ``Constraint Databases, Geometric Elimination and Geographic Information Systems'' was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.

08471 Report – Geographic Privacy-Aware Knowledge Discovery and Delivery

The Dagstuhl-Seminar on Geographic Privacy-Aware Knowledge Discovery and Delivery was held during... more The Dagstuhl-Seminar on Geographic Privacy-Aware Knowledge Discovery and Delivery was held during 16 - 21 November, 2008, with 37 participants registered from various countries from Europe, as well as other parts of the world such as United States, Canada, Argentina, and Brazil. Issues in the newly emerging area of geographic knowledge discovery with a privacy perspective were discussed in a week to consolidate some of the research questions. The Dagstuhl program included plenary sessions and special interest group meetings which continued even late in the evening with heated discussions. The plenary sessions were dedicated for the talks of some of the participants covering a variety of issues in geographic knowledge discovery and delivery. The reports on special interest group meetings (SIG) were also presented and discussed during the plenary sessions.

Constraint Databases and Geographic Information Systems

Constraint databases and geographic information systems share many applications. However, constra... more Constraint databases and geographic information systems share many applications. However, constraint databases can go beyond geographic information systems in efficient spatial and spatiotemporal data handling methods and in advanced applications. This survey mainly describes ways that constraint databases go beyond geographic information systems. However, the survey points out that in some areas constraint databases can learn also from geographic information systems.

Time-Series-Based Queries on Stable Transportation Networks Equipped with Sensors

ISPRS International Journal of Geo-Information, 2021

In this paper, we propose a formalism to query transportation networks that are equipped with sen... more In this paper, we propose a formalism to query transportation networks that are equipped with sensors that produce time-series data. The core of the proposed query mechanism is a logic-based language that is capable to return time, value, and time-series outputs, as well as Boolean queries. We can also use the language for node selection and path selection. Furthermore, we propose an implementation of this language in a graph database system and evaluate its working on a fragment of the Flemish river system that is equipped with sensors that measure the water height at regular moments in time.

Space-Time Prism Model

DEFINITION During the last decade, the proliferation of location-aware devices, such as GPS and s... more DEFINITION During the last decade, the proliferation of location-aware devices, such as GPS and smartphones, has given rise to the collection of huge amounts of moving object data in the form of finite sequences of time-stamped geographical locations. These sequences of space-time points encode (a sample of) the trajectories of moving objects. The location of the moving objects is unknown between these measured space-time points. Several models have been proposed to model the uncertainty of a moving object’s location in between sample points. Linear interpolation between the sample points is a first and obvious example. However, if additional information is available, such as a limit on the possible speed of a moving object, a more informative model is provided by the framework of space-time prisms. This model gives, between two consecutive measured locations, the envelope of possible locations of a moving object in space-time space, given an upper bound on the moving object’s speed...

A Formal Algebra for OLAP

ArXiv, 2016

Online Analytical Processing (OLAP) comprises tools and algorithms that allow querying multidimen... more Online Analytical Processing (OLAP) comprises tools and algorithms that allow querying multidimensional databases. It is based on the multidimensional model, where data can be seen as a cube, where each cell contains one or more measures can be aggregated along dimensions. Despite the extensive corpus of work in the field, a standard language for OLAP is still needed, since there is no well-defined, accepted semantics, for many of the usual OLAP operations. In this paper, we address this problem, and present a set of operations for manipulating a data cube. We clearly define the semantics of these operations, and prove that they can be composed, yielding a language powerful enough to express complex OLAP queries. We express these operations as a sequence of atomic transformations over a fixed multidimensional matrix, whose cells contain a sequence of measures. Each atomic transformation produces a new measure. When a sequence of transformations defines an OLAP operation, a flag is p...

Some fragments of second-order logic over the reals for which satisability and equivalence are (un)decidable

A b s t r a c t. We consider the 1 -fragment of second-order logic over the vocabularyh+;; 0; 1;&... more A b s t r a c t. We consider the 1 -fragment of second-order logic over the vocabularyh+;; 0; 1;<;S1;:::;Ski, interpreted over the reals, where the predicate symbols Si are interpreted as semialgebraic sets. We show that, in this context, satisability of formulas is decidable for the rst-order 9 -quantier fragment and undecidable for the9 8- and8 -fragments. We also show that for these three fragments the same (un)decidability results hold for containment and equivalence of formulas.

Mobility Data Mining and Privacy (Dagstuhl Seminar 12331)

This report documents the program and the outcomes of Dagstuhl Seminar 12331 "Mobility Data ... more This report documents the program and the outcomes of Dagstuhl Seminar 12331 "Mobility Data Mining and Privacy". Mobility data mining aims to extract knowledge from movement behaviour of people, but this data also poses novel privacy risks. This seminar gathered a multidisciplinary team for a conversation on how to balance the value in mining mobility data with privacy issues. The seminar focused on four key issues: Privacy in vehicular data, in cellular data, context-dependent privacy, and use of location uncertainty to provide privacy.

Affine-invariant querying of spatial data using a triangle-based logic

GeoInformatica, 2020

Decidable containment of recursive queries

Theoretical Computer Science, 2005

One of the most important reasoning tasks on queries is checking containment, i.e., verifying whe... more One of the most important reasoning tasks on queries is checking containment, i.e., verifying whether one query yields necessarily a subset of the result of another one. Query containment is crucial in several contexts, such as query optimization, query reformulation, knowledge-base verification, information integration, integrity checking, and cooperative answering. Containment is undecidable in general for Datalog, the fundamental language for expressing recursive queries. On the other hand, it is known that containment between monadic Datalog queries and between Datalog queries and unions of conjunctive queries are decidable. It is also known that containment between unions of conjunctive two-way regular path queries, which are queries used in the context of semistructured data models containing a limited form of recursion in the form of transitive closure, is decidable. In this paper, we combine the automata-theoretic techniques at the base of these two decidability results to show that containment of Datalog in union of conjunctive two-way regular path queries is decidable in 2EXPTIME. By sharpening a known lower bound result for containment of Datalog in union of conjunctive queries we show also a matching lower bound.

First-order complete and computationally complete query languages for spatio-temporal databases

ACM Transactions on Computational Logic, 2008

We address a fundamental question concerning spatio-temporal database systems: “What are exactly ... more We address a fundamental question concerning spatio-temporal database systems: “What are exactly spatio-temporal queries?” We define spatio-temporal queries to be computable mappings that are also generic , meaning that the result of a query may only depend to a limited extent on the actual internal representation of the spatio-temporal data. Genericity is defined as invariance under groups of geometric transformations that preserve certain characteristics of spatio-temporal data (e.g., collinearity, distance, velocity, acceleration, …). These groups depend on the notions that are relevant in particular spatio-temporal database applications. These transformations also have the distinctive property that they respect the monotone and unidirectional nature of time. We investigate different genericity classes with respect to the constraint database model for spatio-temporal databases and we identify sound and complete languages for the first-order and the computable queries in these gen...

Deciding Termination of Query Evaluation in Transitive-Closure Logics for Constraint Databases

Lecture Notes in Computer Science, 2002

We study extensions of first-order logic over the reals with different types of transitive-closur... more We study extensions of first-order logic over the reals with different types of transitive-closure operators as query languages for constraint databases that can be described by Boolean combinations of polynomial inequalities over the reals. We are in particular interested in deciding the termination of the evaluation of queries expressible in these transitive-closure logics. It turns out that termination is undecidable in general. However, we show that the termination of the transitive closure of a continuous function graph in the two-dimensional plane, viewed as a binary relation over the reals, is decidable, and even expressible in first-order logic over the reals. Based on this result, we identify a particular transitive-closure logic for which termination of query evaluation is decidable and which is more expressive than first-order logic over the reals. Furthermore, we can define a guarded fragment in which exactly the terminating queries of this language are expressible.

Constraint databases, geometric elimination and geographic information systems

From 20.05. to 25.05., the Dagstuhl Seminar 07212 Constraint Databases, Geometric Elimination and... more From 20.05. to 25.05., the Dagstuhl Seminar 07212 Constraint Databases, Geometric Elimination and Geographic Information Systems was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The rst section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.

Floris Geerts, University of Limburg Bart Kuijpers, University of Antwerp

Research Issues in Structured and Semistructured Database Programming, 2000

We consider two-dimensional spatial databases defined in terms of polynomial inequalities and foc... more We consider two-dimensional spatial databases defined in terms of polynomial inequalities and focus on the potential of program-ming languages for such databases to express queries related to topo-logical connectivity. It is known that the topological connectivity test is not first-order expressible. One approach to obtain a language in which connectivity queries can be expressed would be to extend FO+ Poly with a generalized (or Lindström) quantifier expressing that two points belong to the same connected component of a given database. ...

Program Chairs of SSTDM-12 Workshop

With advances in remote sensors, sensor networks, and proliferation of location sensing devices i... more With advances in remote sensors, sensor networks, and proliferation of location sensing devices into common walks of lives and businesses, the generation of disparate, dynamic, and geographically distributed spatiotemporal data has exploded in recent years. Knowledge extracted from spatial and spatiotemporal data plays a critical role in our daily lives, whether it is to understand the human implications of global environmental changes, responding to natural disasters, or simply finding alternate routes in case of an emergency ...

Checking the Integrity of Spatial Integrity Constraints

Integrity constraints play a major role when the quality of spatial data is checked by automatic ... more Integrity constraints play a major role when the quality of spatial data is checked by automatic procedures. Nevertheless the possibilities of checking the internal consistency of the integrity constraints themselves are hardly researched jet. This work analyses the applicability of reasoning techniques like the composition of spatial relations and constraint satisfaction in networks of constraints to find conflicts and redundancies in sets of spatial semantic integrity constraints. These integrity rules specify relations among entity classes. Such relations must hold to assure that the data is fitting to the semantics intended by the data model. For spatial data many semantic integrity constraints are based on spatial properties described for example through qualitative topological or metric relations. Since integrity constraints are defined at the class level, the reasoning properties of these spatial relations can not directly be applied. Therefore a set of class relations has be...

Semantic Trajectory Data Mining: a User Driven Approach

Trajectories left behind cars, humans, birds or any other moving object are a new kind of data wh... more Trajectories left behind cars, humans, birds or any other moving object are a new kind of data which can be very useful in decision making process in several application domains. These data, however, are normally available as sample points, and therefore have very little or no semantics. The analysis and knowledge extraction from trajectory sample points is very difficult from the user's point of view, and there is an emerging need for new data models, manipulation techniques, and tools to extract meaningful patterns from these data. In this paper we propose a new methodology for knowledge discovery from trajectories. We propose through a semantic trajectory data mining query language several functionalities to select, preprocess, and transform trajectory sample points into semantic trajectories at higher abstraction levels, in order to allow the user to extract meaningful, understandable, and useful patterns from trajectories. We claim that meaningful patterns can only be extra...

Temporal Support of Regular Expressions in Sequential Pattern Mining

Classic algorithms for sequential pattern discovery,return all frequent sequences present in a da... more Classic algorithms for sequential pattern discovery,return all frequent sequences present in a database. Since, in general, only a few ones are interesting from a user's point of view, languages based on regular expressions (RE) have been proposed to restrict frequent sequences to the ones that satisfy user-specified constraints. Although the support of a sequence is computed as the number of data-sequences satisfying a pattern with respect to the total number of data-sequences in the database, once regular expressions come into play, new approaches to the concept of support are needed. For example, users may be interested in computing the support of the RE as a whole, in addition to the one of a particular pattern. As a simple example, the expression $(A|B).C$ is satisfied by sequences like A.C or B.C. Even though the semantics of this RE suggests that both of them are equally interesting to the user, if neither of them verifies a minimum support although together they do), the...

An analytic solution to the alibi query in the bead model for moving object data

Moving objects produce trajectories, which are stored in databases by means of finite samples of ... more Moving objects produce trajectories, which are stored in databases by means of finite samples of time-stamped locations. When also speed limitations in these sample points are known, beads can be used to model the uncertainty about the object's location in between sample points. In this setting, a query of particular interest, that has been studied in the literature of geographic information systems (GIS), is the alibi query. This boolean query asks whether two moving objects can have physically met. This adds up to deciding whether the necklaces of beads of these objects intersect. This problem can be reduced to deciding whether two beads intersect. Since, existing software to solve this problem fails to answer this question within a reasonable time, we propose an analytical solution to the alibi query, which can be used to answer the alibi query in constant time, a matter of milliseconds or less, for two single beads and in time proportional to the product of their lengths for...

Propagating and measuring anchor uncertainty in space-time prisms on road networks

Space-time prisms capture all possible spatio-temporal locations of a moving object between sampl... more Space-time prisms capture all possible spatio-temporal locations of a moving object between sample points given speed limit constraints on its movement. These sample points are usually considered to be perfect measurements. In this paper we restrict ourselves to a road network and extend the notion of sample points to sample regions, which are bounded, sometimes disconnected, subsets of space-time wherein each point is a possible location, with its respective probability, where a moving object could have originated from or arrived in. This model allows us to model measurement errors, multiple possible simultaneous locations and even flexibility of a moving object. We develop an algorithm that computes the envelope of all space-time prisms that have an anchor in these sample regions and we developed an algorithm that computes for any spatio-temporal point the probability with which a space-time prism, with anchors in these sample regions, contains that point. We implemented these alg...

07212 Abstracts Collection – Constraint Databases, Geometric Elimination ang Geographic Information Systems

From 20.05. to 25.05., the Dagstuhl Seminar 07212 ``Constraint Databases, Geometric Elimination a... more From 20.05. to 25.05., the Dagstuhl Seminar 07212 ``Constraint Databases, Geometric Elimination and Geographic Information Systems'' was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available.

08471 Report – Geographic Privacy-Aware Knowledge Discovery and Delivery

The Dagstuhl-Seminar on Geographic Privacy-Aware Knowledge Discovery and Delivery was held during... more The Dagstuhl-Seminar on Geographic Privacy-Aware Knowledge Discovery and Delivery was held during 16 - 21 November, 2008, with 37 participants registered from various countries from Europe, as well as other parts of the world such as United States, Canada, Argentina, and Brazil. Issues in the newly emerging area of geographic knowledge discovery with a privacy perspective were discussed in a week to consolidate some of the research questions. The Dagstuhl program included plenary sessions and special interest group meetings which continued even late in the evening with heated discussions. The plenary sessions were dedicated for the talks of some of the participants covering a variety of issues in geographic knowledge discovery and delivery. The reports on special interest group meetings (SIG) were also presented and discussed during the plenary sessions.

Constraint Databases and Geographic Information Systems

Constraint databases and geographic information systems share many applications. However, constra... more Constraint databases and geographic information systems share many applications. However, constraint databases can go beyond geographic information systems in efficient spatial and spatiotemporal data handling methods and in advanced applications. This survey mainly describes ways that constraint databases go beyond geographic information systems. However, the survey points out that in some areas constraint databases can learn also from geographic information systems.

Time-Series-Based Queries on Stable Transportation Networks Equipped with Sensors

ISPRS International Journal of Geo-Information, 2021

In this paper, we propose a formalism to query transportation networks that are equipped with sen... more In this paper, we propose a formalism to query transportation networks that are equipped with sensors that produce time-series data. The core of the proposed query mechanism is a logic-based language that is capable to return time, value, and time-series outputs, as well as Boolean queries. We can also use the language for node selection and path selection. Furthermore, we propose an implementation of this language in a graph database system and evaluate its working on a fragment of the Flemish river system that is equipped with sensors that measure the water height at regular moments in time.

Space-Time Prism Model

DEFINITION During the last decade, the proliferation of location-aware devices, such as GPS and s... more DEFINITION During the last decade, the proliferation of location-aware devices, such as GPS and smartphones, has given rise to the collection of huge amounts of moving object data in the form of finite sequences of time-stamped geographical locations. These sequences of space-time points encode (a sample of) the trajectories of moving objects. The location of the moving objects is unknown between these measured space-time points. Several models have been proposed to model the uncertainty of a moving object’s location in between sample points. Linear interpolation between the sample points is a first and obvious example. However, if additional information is available, such as a limit on the possible speed of a moving object, a more informative model is provided by the framework of space-time prisms. This model gives, between two consecutive measured locations, the envelope of possible locations of a moving object in space-time space, given an upper bound on the moving object’s speed...

A Formal Algebra for OLAP

ArXiv, 2016

Online Analytical Processing (OLAP) comprises tools and algorithms that allow querying multidimen... more Online Analytical Processing (OLAP) comprises tools and algorithms that allow querying multidimensional databases. It is based on the multidimensional model, where data can be seen as a cube, where each cell contains one or more measures can be aggregated along dimensions. Despite the extensive corpus of work in the field, a standard language for OLAP is still needed, since there is no well-defined, accepted semantics, for many of the usual OLAP operations. In this paper, we address this problem, and present a set of operations for manipulating a data cube. We clearly define the semantics of these operations, and prove that they can be composed, yielding a language powerful enough to express complex OLAP queries. We express these operations as a sequence of atomic transformations over a fixed multidimensional matrix, whose cells contain a sequence of measures. Each atomic transformation produces a new measure. When a sequence of transformations defines an OLAP operation, a flag is p...

Some fragments of second-order logic over the reals for which satisability and equivalence are (un)decidable

A b s t r a c t. We consider the 1 -fragment of second-order logic over the vocabularyh+;; 0; 1;&... more A b s t r a c t. We consider the 1 -fragment of second-order logic over the vocabularyh+;; 0; 1;<;S1;:::;Ski, interpreted over the reals, where the predicate symbols Si are interpreted as semialgebraic sets. We show that, in this context, satisability of formulas is decidable for the rst-order 9 -quantier fragment and undecidable for the9 8- and8 -fragments. We also show that for these three fragments the same (un)decidability results hold for containment and equivalence of formulas.

Mobility Data Mining and Privacy (Dagstuhl Seminar 12331)

This report documents the program and the outcomes of Dagstuhl Seminar 12331 "Mobility Data ... more This report documents the program and the outcomes of Dagstuhl Seminar 12331 "Mobility Data Mining and Privacy". Mobility data mining aims to extract knowledge from movement behaviour of people, but this data also poses novel privacy risks. This seminar gathered a multidisciplinary team for a conversation on how to balance the value in mining mobility data with privacy issues. The seminar focused on four key issues: Privacy in vehicular data, in cellular data, context-dependent privacy, and use of location uncertainty to provide privacy.

Affine-invariant querying of spatial data using a triangle-based logic

GeoInformatica, 2020