Information Technology Reference
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Fig. 3.52 Schema translation of categorization
attribute declared as #REQUIRED referred by their common element's IDREF in
DTD as shown in Fig. 3.52 .
Rule 9: Mapping N-ary Relationship from RDB to XML
Multiple tables relate to each other in an n-ary relationship. An n-ary relationship
is a relationship relation for multiple tables such that components of the former's
compound primary key addressing to the primary keys of the latter, which are re-
lated to each other. In DTD, we transform n-ary relationship into group of element
as shown in Fig. 3.53 .
3.8
Case Study of Translating a Relational Schema into a
Document Type Definition
Consider a case study of a hospital database system. In this system, a patient can
have many record folders. Each record folder can contain many different medical
records of the patient. The AE, a ward, and an outpatient record can be generalized
as a medical record. A country has many patients. A borrower of the record folder
of the patient can be a department, a doctor, or other hospital for their references or
checking. Once a record folder is borrowed, a loan history is created to record the
details about it. The relational schemas for this case study are shown below. Notice
that underlined and italic means primary key and * means foreign key.
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