Databases Reference
In-Depth Information
Figure 5: A DTD graph.
4.2 Methods for Mapping XML Documents into Relational
Databases without the Knowledge of DTDs
Florescu and Kossmann reported the result of performance evaluation of several
alternative ways to store XML documents into relational databases
7)
. The
alternative ways they studied do not use the information of DTDs. XML documents
are modeled as a tree as shown in Figure 2. For simplicity, the distinction of elements
and XML attributes is blurred. Florescu and Kossmann identified two axes for
classifying mappings of tree data into relational schemas: one is mapping edges
and the other is mapping values. They listed up the following three approaches to
mapping edges:
(E
e
)
Edge Approach
A relation is created for storing information of edges in a tree. Each edge is
stored as a tuple in the relation.
(E
b
)
Binary Approach
Edges are clusterd according to element names (or XML attribute names) of
their destination nodes. A relation is created for each cluster.
(E
u
)
Universal Table
A relation is created which have attributes for every elements and XML
attributes in the target XML document.
