7,529 research outputs found
A General Approach for Securely Querying and Updating XML Data
Over the past years several works have proposed access control models for XML
data where only read-access rights over non-recursive DTDs are considered. A
few amount of works have studied the access rights for updates. In this paper,
we present a general model for specifying access control on XML data in the
presence of update operations of W3C XQuery Update Facility. Our approach for
enforcing such updates specifications is based on the notion of query rewriting
where each update operation defined over arbitrary DTD (recursive or not) is
rewritten to a safe one in order to be evaluated only over XML data which can
be updated by the user. We investigate in the second part of this report the
secure of XML updating in the presence of read-access rights specified by a
security views. For an XML document, a security view represents for each class
of users all and only the parts of the document these users are able to see. We
show that an update operation defined over a security view can cause disclosure
of sensitive data hidden by this view if it is not thoroughly rewritten with
respect to both read and update access rights. Finally, we propose a security
view based approach for securely updating XML in order to preserve the
confidentiality and integrity of XML data.Comment: No. RR-7870 (2012
Semantic Query Reformulation in Social PDMS
We consider social peer-to-peer data management systems (PDMS), where each
peer maintains both semantic mappings between its schema and some
acquaintances, and social links with peer friends. In this context,
reformulating a query from a peer's schema into other peer's schemas is a hard
problem, as it may generate as many rewritings as the set of mappings from that
peer to the outside and transitively on, by eventually traversing the entire
network. However, not all the obtained rewritings are relevant to a given
query. In this paper, we address this problem by inspecting semantic mappings
and social links to find only relevant rewritings. We propose a new notion of
'relevance' of a query with respect to a mapping, and, based on this notion, a
new semantic query reformulation approach for social PDMS, which achieves great
accuracy and flexibility. To find rapidly the most interesting mappings, we
combine several techniques: (i) social links are expressed as FOAF (Friend of a
Friend) links to characterize peer's friendship and compact mapping summaries
are used to obtain mapping descriptions; (ii) local semantic views are special
views that contain information about external mappings; and (iii) gossiping
techniques improve the search of relevant mappings. Our experimental
evaluation, based on a prototype on top of PeerSim and a simulated network
demonstrate that our solution yields greater recall, compared to traditional
query translation approaches proposed in the literature.Comment: 29 pages, 8 figures, query rewriting in PDM
View Selection in Semantic Web Databases
We consider the setting of a Semantic Web database, containing both explicit
data encoded in RDF triples, and implicit data, implied by the RDF semantics.
Based on a query workload, we address the problem of selecting a set of views
to be materialized in the database, minimizing a combination of query
processing, view storage, and view maintenance costs. Starting from an existing
relational view selection method, we devise new algorithms for recommending
view sets, and show that they scale significantly beyond the existing
relational ones when adapted to the RDF context. To account for implicit
triples in query answers, we propose a novel RDF query reformulation algorithm
and an innovative way of incorporating it into view selection in order to avoid
a combinatorial explosion in the complexity of the selection process. The
interest of our techniques is demonstrated through a set of experiments.Comment: VLDB201
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