Schemas Integration - Information Systems Reengineering, Integration and Normalization - page 270

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Fig. 7.9 Merge EER models by subtype

domain B will be in domain A only and any element that exists in domain B will be
also in domain A. (Fig. 7.9 )

Substep 2.4. Merge entities by aggregation.
X is an aggregation of B1, B2, and R(B). Entities A and B and their relationships
are preserved in the transformed schema X. There is a bidirectional one-to-one
mapping between elements of A, (B1, B2 R(B)), and (X1, X2, R(X)) by introduc-
ing a common key field. It is able to recover the instance of x, which is derived
from either B1 or B2. X1 dominates the (B1and B2) to ensure that information is
preserved after schema is transformed and X is proved to be an equivalent to (A,
B) (Fig. 7.10 ).

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