33 research outputs found
Inference of Shape Graphs for Graph Databases
We investigate the problem of constructing a shape graph that describes the structure of a given graph database. We employ the framework of grammatical inference, where the objective is to find an inference algorithm that is both sound, i.e., always producing a schema that validates the input graph, and complete, i.e., able to produce any schema, within a given class of schemas, provided that a sufficiently informative input graph is presented. We identify a number of fundamental limitations that preclude feasible inference. We present inference algorithms based on natural approaches that allow to infer schemas that we argue to be of practical importance
Prioritized Repairing and Consistent Query Answering in Relational Databases
A consistent query answer in an inconsistent database is an answer obtained
in every (minimal) repair. The repairs are obtained by resolving all conflicts
in all possible ways. Often, however, the user is able to provide a preference
on how conflicts should be resolved. We investigate here the framework of
preferred consistent query answers, in which user preferences are used to
narrow down the set of repairs to a set of preferred repairs. We axiomatize
desirable properties of preferred repairs. We present three different families
of preferred repairs and study their mutual relationships. Finally, we
investigate the complexity of preferred repairing and computing preferred
consistent query answers.Comment: Accepted to the special SUM'08 issue of AMA
Deciding Equivalence of Linear Tree-to-Word Transducers in Polynomial Time
We show that the equivalence of deterministic linear top-down tree-to-word
transducers is decidable in polynomial time. Linear tree-to-word transducers
are non-copying but not necessarily order-preserving and can be used to express
XML and other document transformations. The result is based on a partial normal
form that provides a basic characterization of the languages produced by linear
tree-to-word transducers.Comment: short version of this paper will be published in the proceedings of
the 20th Conference on Developments in Language Theory (DLT 2016), Montreal,
Canad
Bounded repairability for regular tree languages
We study the problem of bounded repairability of a given restriction tree language R into a target tree language T. More precisely, we say that R is bounded repairable w.r.t. T if there exists a bound on the number of standard tree editing operations necessary to apply to any tree in R in order to obtain a tree in T. We consider a number of possible specifications for tree languages: bottom-up tree automata (on curry encoding of unranked trees) that capture the class of XML Schemas and DTDs. We also consider a special case when the restriction language R is universal, i.e., contains all trees over a given alphabet. We give an effective characterization of bounded repairability between pairs of tree languages represented with automata. This characterization introduces two tools, synopsis trees and a coverage relation between them, allowing one to reason about tree languages that undergo a bounded number of editing operations. We then employ this characterization to provide upper bounds to the complexity of deciding bounded repairability and we show that these bounds are tight. In particular, when the input tree languages are specified with arbitrary bottom-up automata, the problem is coNEXPTIME-complete. The problem remains coNEXPTIME-complete even if we use deterministic non-recursive DTDs to specify the input languages. The complexity of the problem can be reduced if we assume that the alphabet, the set of node labels, is fixed: the problem becomes PSPACE-complete for non-recursive DTDs and coNP-complete for deterministic non-recursive DTDs. Finally, when the restriction tree language R is universal, we show that the bounded repairability problem becomes EXPTIME-complete if the target language is specified by an arbitrary bottom-up tree automaton and becomes tractable (PTIME-complete, in fact) when a deterministic bottom-up automaton is used
On Functionality of Visibly Pushdown Transducers
Visibly pushdown transducers form a subclass of pushdown transducers that
(strictly) extends finite state transducers with a stack. Like visibly pushdown
automata, the input symbols determine the stack operations. In this paper, we
prove that functionality is decidable in PSpace for visibly pushdown
transducers. The proof is done via a pumping argument: if a word with two
outputs has a sufficiently large nesting depth, there exists a nested word with
two outputs whose nesting depth is strictly smaller. The proof uses technics of
word combinatorics. As a consequence of decidability of functionality, we also
show that equivalence of functional visibly pushdown transducers is
Exptime-Complete.Comment: 20 page
Introducing Preference-Based Argumentation to Inconsistent Ontological Knowledge Bases
International audienceHandling inconsistency is an inherent part of decision making in traditional agri-food chains â due to the various concerns involved. In order to explain the source of inconsistency and represent the existing conflicts in the ontological knowledge base, argumentation theory can be used. However, the current state of art methodology does not allow to take into account the level of significance of the knowledge expressed by the various ontological knowledge sources. We propose to use preferences in order to model those differences between formulas and evaluate our proposal practically by implementing it within the INRA platform and showing a use case using this formalism in a bread making decision support system
Schemas for Unordered XML on a DIME
We investigate schema languages for unordered XML having no relative order
among siblings. First, we propose unordered regular expressions (UREs),
essentially regular expressions with unordered concatenation instead of
standard concatenation, that define languages of unordered words to model the
allowed content of a node (i.e., collections of the labels of children).
However, unrestricted UREs are computationally too expensive as we show the
intractability of two fundamental decision problems for UREs: membership of an
unordered word to the language of a URE and containment of two UREs.
Consequently, we propose a practical and tractable restriction of UREs,
disjunctive interval multiplicity expressions (DIMEs).
Next, we employ DIMEs to define languages of unordered trees and propose two
schema languages: disjunctive interval multiplicity schema (DIMS), and its
restriction, disjunction-free interval multiplicity schema (IMS). We study the
complexity of the following static analysis problems: schema satisfiability,
membership of a tree to the language of a schema, schema containment, as well
as twig query satisfiability, implication, and containment in the presence of
schema. Finally, we study the expressive power of the proposed schema languages
and compare them with yardstick languages of unordered trees (FO, MSO, and
Presburger constraints) and DTDs under commutative closure. Our results show
that the proposed schema languages are capable of expressing many practical
languages of unordered trees and enjoy desirable computational properties.Comment: Theory of Computing System
Querying regular sets of XML documents
info:eu-repo/semantics/publishe
Proceedings of 4th International Workshop on Logic in Databases (LID 2011), Uppsala, Sweden, March 25, 2011
This volume contains the proceedings of the 4th International Workshop on Logic in Databases (LID 2011), held on 25 March 2011, in Uppsala, Sweden, as a collocated event of the joint ICDT/EDBT 2011 conferences. The workshop program consists of keynote talks by James Cheney (University of Edinburgh, UK) and Phokion Kolaitis (University of California, Santa Cruz & IBM Research Almaden, USA), and the presentation of regular and short papers by workshop participants. LID continues to present high-quality work focusing on logical aspects of data management. In response to the call for papers, eleven papers were received. Each submission was reviewed by at least three program committee members and external reviewers. Six papers were accepted for regular and four for short paper presentation
Typing regular path query languages for data graphs
Regular path query languages for data graphs are essentially untyped. The lack of type information greatly limits the optimization opportunities for query engines and makes application development more complex. In this paper we discuss a simple, yet expressive, schema language for edge-labelled data graphs. This schema language is, then, used to define a query type inference approach with good precision properties