325 research outputs found
Extended RDF: Computability and Complexity Issues
ERDF stable model semantics is a recently proposed semantics for
ERDF ontologies and a faithful extension of RDFS semantics on RDF graphs.
In this paper, we elaborate on the computability and complexity issues of the
ERDF stable model semantics. Based on the undecidability result of ERDF
stable model semantics, decidability under this semantics cannot be achieved,
unless ERDF ontologies of restricted syntax are considered. Therefore, we
propose a slightly modified semantics for ERDF ontologies, called ERDF #n-
stable model semantics. We show that entailment under this semantics is, in
general, decidable and also extends RDFS entailment. Equivalence statements
between the two semantics are provided. Additionally, we provide algorithms
that compute the ERDF #n-stable models of syntax-restricted and general
ERDF ontologies. Further, we provide complexity results for the ERDF #nstable
model semantics on syntax-restricted and general ERDF ontologies.
Finally, we provide complexity results for the ERDF stable model semantics
on syntax-restricted ERDF ontologies
Reasoning & Querying – State of the Art
Various query languages for Web and Semantic Web data, both for practical use and as an area of research in the scientific community, have emerged in recent years. At the same time, the broad adoption of the internet where keyword search is used in many applications, e.g. search engines, has familiarized casual users with using keyword queries to retrieve information on the internet. Unlike this easy-to-use querying, traditional query languages require knowledge of the language itself as well as of the data to be queried. Keyword-based query languages for XML and RDF bridge the gap between the two, aiming at enabling simple querying of semi-structured data, which is relevant e.g. in the context of the emerging Semantic Web. This article presents an overview of the field of keyword querying for XML and RDF
Graph Pattern Matching in GQL and SQL/PGQ
As graph databases become widespread, JTC1 -- the committee in joint charge
of information technology standards for the International Organization for
Standardization (ISO), and International Electrotechnical Commission (IEC) --
has approved a project to create GQL, a standard property graph query language.
This complements a project to extend SQL with a new part, SQL/PGQ, which
specifies how to define graph views over an SQL tabular schema, and to run
read-only queries against them.
Both projects have been assigned to the ISO/IEC JTC1 SC32 working group for
Database Languages, WG3, which continues to maintain and enhance SQL as a
whole. This common responsibility helps enforce a policy that the identical
core of both PGQ and GQL is a graph pattern matching sub-language, here termed
GPML.
The WG3 design process is also analyzed by an academic working group, part of
the Linked Data Benchmark Council (LDBC), whose task is to produce a formal
semantics of these graph data languages, which complements their standard
specifications.
This paper, written by members of WG3 and LDBC, presents the key elements of
the GPML of SQL/PGQ and GQL in advance of the publication of these new
standards
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