Jan Paredaens’s research while affiliated with University of Antwerp and other places

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Publications (174)


Figure 1: Equivalence Classes of the diï¿¿erent sets of features where an ascending path denotes subsumption; absence of such a path denotes non-subsumption.
Expressiveness within Sequence Datalog
  • Preprint
  • File available

June 2022

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22 Reads

Heba Aamer

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Jan Paredaens

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Motivated by old and new applications, we investigate Datalog as a language for sequence databases. We reconsider classical features of Datalog programs, such as negation, recursion, intermediate predicates, and relations of higher arities. We also consider new features that are useful for sequences, notably, equations between path expressions, and "packing". Our goal is to clarify the relative expressiveness of all these different features, in the context of sequences. Towards our goal, we establish a number of redundancy and primitivity results, showing that certain features can, or cannot, be expressed in terms of other features. These results paint a complete picture of the expressiveness relationships among all possible Sequence Datalog fragments that can be formed using the six features that we consider.

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J-Logic: a Logic for Querying JSON

June 2020

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95 Reads

We propose a logical framework, based on Datalog, to study the foundations of querying JSON data. The main feature of our approach, which we call J-Logic, is the emphasis on paths. Paths are sequences of keys and are used to access the tree structure of nested JSON objects. J-Logic also features ``packing'' as a means to generate a new key from a path or subpath. J-Logic with recursion is computationally complete, but many queries can be expressed without recursion, such as deep equality. We give a necessary condition for queries to be expressible without recursion. Most of our results focus on the deterministic nature of JSON objects as partial functions from keys to values. Predicates defined by J-Logic programs may not properly describe objects, however. Nevertheless we show that every object-to-object transformation in J-Logic can be defined using only objects in intermediate results. Moreover we show that it is decidable whether a positive, nonrecursive J-Logic program always returns an object when given objects as inputs. Regarding packing, we show that packing is unnecessary if the output does not require new keys. Finally, we show the decidability of query containment for positive, nonrecursive J-Logic programs.


Calculi for symmetric queries

April 2019

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13 Reads

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1 Citation

Journal of Computer and System Sciences

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Jelle Hellings

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Jan Paredaens

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[...]

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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 yields an incidence-based normal form for QuineCALC queries. More generally, we propose counting-only queries as those SyCALC queries the result of which only depends on incidence information, and characterize them as quantified Boolean combinations of QuineCALC queries. A normal form is proposed for them too. It turns out to be undecidable whether a SyCALC query is counting-only, but decidable whether a counting-only query is a QuineCALC query. Finally, some classical decidability problems are considered which are shown to be undecidable for SyCALC, but decidable for QuineCALC and counting-only queries.


J-Logic: Logical Foundations for JSON Querying

May 2017

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493 Reads

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15 Citations

We propose a logical framework, based on Datalog, to study the foundations of querying JSON data. The main feature of our approach, which we call J-Logic, is the emphasis on paths. Paths are sequences of keys and are used to access the tree structure of nested JSON objects. J-Logic also features "packing" as a means to generate a new key from a path or subpath. J-Logic with recursion is computationally complete, but many queries can be expressed without recursion, such as deep equality. We give a necessary condition for queries to be expressible without recursion. Most of our results focus on the deterministic nature of JSON objects as partial functions from keys to values. Predicates defined by J-Logic programs may not properly describe objects, however. Nevertheless we show that every object-to-object transformation in J-Logic can be defined using only objects in intermediate results. Moreover we show that it is decidable whether a positive, nonrecursive J-Logic program always returns an object when given objects as inputs. Regarding packing, we show that packing is unnecessary if the output does not require new keys. Finally, we show the decidability of query containment for positive, nonrecursive J-Logic programs.


Figure 2. XML store St 1
A Formal and Unified Description of XML Manipulation Languages

August 2016

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38 Reads

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1 Citation

Fundamenta Informaticae

We discuss three well-known languages for querying and manipulatingXML documents: XQuery, XPath and XSLT. They are considered to be the standard languages for processing XML documents. However, specifying their complete semantics in a formal way seems almost impossible. Indeed, an attempt by the W3C XML Query Working Group to do so for XQuery was ultimately abandoned. We introduce three sublanguages, called MiXPath, MiXQuery and MiXSLT, and describe their syntax and formal semantics. The syntax and semantics of these languages are chosen such that they are consistent with the ones given in the relatedW3C recommendations. As such this provides a practical foundation for research and teaching of XML languages. For this purpose the sublanguages are chosen such that they contain the most crucial features, constructs and expressions of each of these three languages.



Implication and axiomatization of functional and constant constraints

August 2015

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18 Reads

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13 Citations

Annals of Mathematics and Artificial Intelligence

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 setting of relations with arbitrary arity. We further introduce constant constraints and study the functional and constant constraints combined. Our main results are sound and complete axiomatizations for the functional and constant constraints, both separately and combined. These axiomatizations are derived using the chase algorithm for equality-generating constraints. For derivations of constant constraints, we show how every chase step can be simulated by a bounded number of applications of inference rules. For derivations of functional constraints, we show that the chase algorithm can be normalized to a more specialized symmetry-preserving chase algorithm performing so-called symmetry-preserving steps. We then show how each symmetry-preserving step can be simulated by a bounded number of applications of inference rules. The axiomatization for functional constraints is in particular applicable to the RDF data model, solving a major open problem of Akhtar et al.


Structural characterizations of the navigational expressiveness of relation algebras on a tree

February 2015

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64 Reads

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7 Citations

Journal of Computer and System Sciences

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 binary relation on its nodes is definable by an expression in these algebras. Since each pair of nodes in such a relation represents a unique path in D, our results therefore capture the sets of paths in D definable in each of the fragments. We refer to this perspective on language semantics as the "global view." In contrast with this global view, there is also a "local view" where one is interested in the nodes to which one can navigate starting from a particular node in the document. In this view, we characterize when a set of nodes in D can be defined as the result of applying an expression to a given node of D. All these definability results, both in the global and the local view, are obtained by using a robust two-step methodology, which consists of first characterizing when two nodes cannot be distinguished by an expression in the respective fragments of XPath, and then bootstrapping these characterizations to the desired results.


Implication and Axiomatization of Functional Constraints on Patterns with an Application to the RDF Data Model

March 2014

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6 Reads

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12 Citations

Lecture Notes in Computer Science

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 general setting of relations with arbitrary arity. We show that a chase algorithm for functional constraints can be normalized to a more specialized symmetry-preserving chase algorithm. This symmetry-preserving chase algorithm is subsequently used to construct a sound and complete axiomatization for the functional constraints. This axiomatization is in particular applicable in the RDF data model, solving a major open problem of Akhtar et al.


Citations (69)


... Post-mortem checking targets only full (completed) executions on a historical log. Compliance monitoring checks the execution of the currently running process instances, for a live log. 4 There is a striking similarity between the problem of compliance monitoring and the problem of incremental view maintenance, a well-researched problem in 3 One should differentiate between the problems of verification and compliance checking. Our focus is on compliance checking: checking properties of execution logs. ...

Reference:

What Can Database Query Processing Do for Instance-Spanning Constraints?
Expressiveness within Sequence Datalog
  • Citing Conference Paper
  • June 2021

... We need such syntactically defined languages for this purpose to ensure that we can easily decide whether an arbitrary SyCALC satisfies the relevant syntactic restrictions. In contrast, it follows readily from a result by Gyssens et al. [12] that it is already undecidable whether an arbitrary SyCALC query belongs to the semantically defined language 1-SyCALC. 6 Gyssens et al. [13] introduced the single-object-variable fragment of QuineCALC as a first-order query language that provides a conservative extension of the symmetric Boolean functions of Quine [22], hence the name. ...

Calculi for symmetric queries
  • Citing Article
  • April 2019

Journal of Computer and System Sciences

... Still, in the PDBs we consider in this paper, database instances themselves (the concrete outcomes, or realizations of a PDB) are always finite collections of facts. The framework we discribe here is not suitable for discussing probability spaces over infinite database instances in the sense of [AHV95, Section 5.6], such as constraint databases [KLP00]. We first construct the measurable space of facts over τ and U. ...

Constraint Databases
  • Citing Book
  • January 2000

... One part is the storage and query of fault information, that is, the information is classified and written into the XML document by using the tag, so that the fault information has certain structural relationships such as inclusion, connection and dependence through the element tag. At this time, the XML document will be modeled as an annotated diagram, which is actually a tree sequence, and each tree represents a document or element [13]. When making IETM system, data module code, information control code, information type and metadata information are written and stored in XML. ...

A Formal and Unified Description of XML Manipulation Languages

Fundamenta Informaticae

... { A second approach maintains the chosen theory and extend the underlying language 1,17]. Unfortunately, naive extensions of FO + lpoly cease to remain sound with respect to linear queries (i.e., mapping between databases represented by lpoly) and yield a language equivalent in expressive power to FO + poly 1,20]. ...

Euclid, Tarski, and Engeler encompassed (Preliminary report)
  • Citing Conference Paper
  • January 1998

Lecture Notes in Computer Science

... For relational data, there is a lot of work on chase. The chase for RDF and graph data was studied in [16], [11,14], [7] and [12]. We plan to define a new chase that can be applied to reason about the constraints we defined here. ...

Implication and axiomatization of functional and constant constraints
  • Citing Article
  • August 2015

Annals of Mathematics and Artificial Intelligence

... Motivated by the above, we believe that the class of counting-only queries deserves a broader understanding. Our notion of k-counting-only queries, k ≥ 0, significantly generalizes the notion of counting-only queries of Gyssens et al. [13], which only captures the case k = 1 in this present work. ...

An Approach towards the Study of Symmetric Queries

Proceedings of the VLDB Endowment

... Relation algebraic methods have also been useful in proving metamathematical results, for example that for all n ≥ 3 there are sentences involving only 3 variables whose formal proofs require n variables [14]. In addition, relation algebras and their generalisations have numerous practical applications in computer science, for example in verification [9], computation tasks involving finite topologies [2], and navigation of XML documents [6], to name just a few. ...

Structural characterizations of the navigational expressiveness of relation algebras on a tree
  • Citing Article
  • February 2015

Journal of Computer and System Sciences