Schemas Integration - Information Systems Reengineering, Integration and Normalization - page 298

Case 3. Multiple Matching Elements Between Schemas A and B
Step 1. Multiple matching elements integration
In this step, it shows more than one matching elements in schema A and schema
B. For the first matching element, it is same as case 2. For another matching ele-
ments, the solution is to add a new element for each pair of matching element and
under the root element of integrated schema AB, and add a key reference (keyref) to
the match element in schema A and schema B (Fig. 7.29 ).
Step 2. Path Expression to Access Two XML Documents
In this case, the query statement is analyzed as a path expression without predicates.
The last element R A in the path expression is a root of the integrated document.
Therefore, the whole integrated XML document will be retrieved. As E AB1 is the
first matching element which belongs to documents A and B, the global query will
be decomposed into two subqueries. Two subqueries will be executed to two differ-
ent XML documents. In addition, the element R B is reversed. Therefore, the third
query is required for generating reversed tree (Fig. 7.30 ).
Step 3. Integration for Multiple Matching Elements
In this case, the integrated document contains more than one matching elements
between documents A and B. For the first matching element, the action of data
integration is same as case 2. For the remaining matching elements, they will not
be integrated and added a key reference. The collection of key elements is created
under the root (Fig. 7.31 ).