Schema Translation - Information Systems Reengineering, Integration and Normalization - page 113

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Fig. 3.42 Schema translation of weak entity

hierarchy structure. Each attribute of the relevant entity is mapped into the attribute
of the corresponding element. In the example, this selected XML view and its rel-
evant relations can be mapped as elements of an XML schema. The relevance of the
relations depends on the connectivity and the constraints of the hierarchical tree of
the elements The one-to-many cardinality can be mapped into one parent and many
child elements, and the many-to-one cardinality can be mapped into a one parent
and one child elements of a translated XML schema.

Rule 2: Mapping Weak Entity from RDB to DTD
A weak entity depends on its strong entity such that the primary key of the weak
entity is also a foreign key addressing to the primary key of its strong entity, and
cannot be a null value. In DTD, we transform the strong entity into an element with
ID and the weak entity into another element that refers to the ID element using
IDREF as shown in Fig. 3.42 .

Rule 3: Mapping Participation from RDB to DTD
A child table is in total participation with a parent table provided that all data oc-
currences of the child table must participate in a relationship with the parent table.
A foreign key of a child table in total participation must address to the primary key
of its parent table and cannot be a null value. A child table is in partial participa-