4,802 research outputs found
Constraint-based Query Distribution Framework for an Integrated Global Schema
Distributed heterogeneous data sources need to be queried uniformly using
global schema. Query on global schema is reformulated so that it can be
executed on local data sources. Constraints in global schema and mappings are
used for source selection, query optimization,and querying partitioned and
replicated data sources. The provided system is all XML-based which poses query
in XML form, transforms, and integrates local results in an XML document.
Contributions include the use of constraints in our existing global schema
which help in source selection and query optimization, and a global query
distribution framework for querying distributed heterogeneous data sources.Comment: The Proceedings of the 13th INMIC 2009), Dec. 14-15, 2009, Islamabad,
Pakistan. Pages 1 - 6 Print ISBN: 978-1-4244-4872-2 INSPEC Accession Number:
11072575 Date of Current Version : 15 January 201
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
Validation of schema mappings with nested queries
With the emergence of the Web and the wide use of XML for representing data, the ability to map not only flat relational but also nested data has become crucial. The design of schema mappings is a semi-automatic process. A human designer is needed to guide the process, choose among mapping candidates, and successively refine the mapping. The designer needs a way to figure out whether the mapping is what was intended. Our approach to mapping validation allows the designer to check whether the mapping satisfies certain desirable properties. In this paper, we focus on the validation of mappings between nested relational schemas, in which the mapping assertions are either inclusions or equalities of nested queries. We focus on the nested relational setting since most XMLâs Document Type Definitions (DTDs) can be represented in this model. We perform the validation by reasoning on the schemas and mapping definition. We take into account the integrity constraints defined on both the source and target schema.Preprin
Identification of Design Principles
This report identifies those design principles for a (possibly new) query and transformation
language for the Web supporting inference that are considered essential. Based upon these
design principles an initial strawman is selected. Scenarios for querying the Semantic Web
illustrate the design principles and their reflection in the initial strawman, i.e., a first draft of
the query language to be designed and implemented by the REWERSE working group I4
A semantic and agent-based approach to support information retrieval, interoperability and multi-lateral viewpoints for heterogeneous environmental databases
PhDData stored in individual autonomous databases often needs to be combined and
interrelated. For example, in the Inland Water (IW) environment monitoring domain,
the spatial and temporal variation of measurements of different water quality indicators
stored in different databases are of interest. Data from multiple data sources is more
complex to combine when there is a lack of metadata in a computation forin and when
the syntax and semantics of the stored data models are heterogeneous. The main types
of information retrieval (IR) requirements are query transparency and data
harmonisation for data interoperability and support for multiple user views. A
combined Semantic Web based and Agent based distributed system framework has
been developed to support the above IR requirements. It has been implemented using
the Jena ontology and JADE agent toolkits. The semantic part supports the
interoperability of autonomous data sources by merging their intensional data, using a
Global-As-View or GAV approach, into a global semantic model, represented in
DAML+OIL and in OWL. This is used to mediate between different local database
views. The agent part provides the semantic services to import, align and parse
semantic metadata instances, to support data mediation and to reason about data
mappings during alignment. The framework has applied to support information
retrieval, interoperability and multi-lateral viewpoints for four European environmental
agency databases.
An extended GAV approach has been developed and applied to handle queries that can
be reformulated over multiple user views of the stored data. This allows users to
retrieve data in a conceptualisation that is better suited to them rather than to have to
understand the entire detailed global view conceptualisation. User viewpoints are
derived from the global ontology or existing viewpoints of it. This has the advantage
that it reduces the number of potential conceptualisations and their associated
mappings to be more computationally manageable. Whereas an ad hoc framework
based upon conventional distributed programming language and a rule framework
could be used to support user views and adaptation to user views, a more formal
framework has the benefit in that it can support reasoning about the consistency,
equivalence, containment and conflict resolution when traversing data models. A
preliminary formulation of the formal model has been undertaken and is based upon
extending a Datalog type algebra with hierarchical, attribute and instance value
operators. These operators can be applied to support compositional mapping and
consistency checking of data views. The multiple viewpoint system was implemented
as a Java-based application consisting of two sub-systems, one for viewpoint
adaptation and management, the other for query processing and query result
adjustment
- âŠ