SEKE 2012 Proceedings - Knowledge Systems Institute

specialist intervention. The work at [10] classifies the conflicts
during the integration of XML schemas and proposes
a resolution mechanism using XQuery.
The approach in [9] performs a division of mappings.
This technique decomposes the document into sub-trees.
Joint operations are represented by an undirected graph with
acyclic handling algorithms to solve conflicts. An XML
framework proposed in [13] defines data integration based
on the overall schema, a set of XML data and a set of mappings.
They define an identification function that aims at
globally identifying nodes coming from different sources.
To solve the problem of heterogeneity, this paper
presents a ontology-based approach, which can be used to
improve traditional techniques of XML mapping and storage
into RDB. The purpose of using ontologies is to explicit
the resource content regardless of how the information is
structurally stored. This approach adds semantics to the
XML files while reduces unneeded structural information
to map the XML data to the relational format.
3 Background
To avoid submitting different XQuery queries, we propose
to store XML data in a RDB. By mapping the XML
structure to the relational model, only one SQL query is
posed into the DB. To provide this solution, we need to define
a set of transformation rules that map the XML structure
to a collection of tables and columns.
However, XML documents related to the same application
domain may present different structures, making the
mapping process more difficult. To overcome this issue, the
X2Rel framework provides the following functionalities, as
described in Figure 1:
Figure 1. X2Rel framework architecture [6].
The OntoGen and OntoRel components are finished and
published works. The QMap module is an ongoing project.
The focus of this paper is to present the XMap component,
as described in the next section.
4 The XMap Component
The XMap component uses as input the original XML
files, the global ontology generated by OntoGen and the relational
schema created by OntoRel. In order to specify the
concept equivalences between the XML documents, the ontology
and the relational schema, our approch is based on
a mapping document, as later detailed in Section 4.2. The
insertion of XML data into the RDB is structured in five
ascending levels, as described in Figure 2.
• Integrate the XML files into a global schema, described
by a OWL ontology. Provided by the OntoGen
component, this module receives a set of XML files
and produces the ontology (integrated schema) [7];
• Translate the OWL ontology to a relational schema.
Provided by the OntoRel component, this module receives
the ontology and produces the relational schema
(a SQL script with the create table statements) [6];
• Map and insert the original XML files into the RDB.
Provided by the XMap component, this module receives
the XML files, the ontology and the relational
schema and produces the SQL script with a set of insert
statements;
• And finally map the original XML queries into equivalent
SQL statements. Provided by the QMap component,
this module receives a XQuery statement and
produces a corresponding SQL statement.
Figure 2. The XMap Architecture
The first level associates the input data. The integrated
representation of such documents is responsible for speci-
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