Database Management System Emulation - Information Systems Reengineering, Integration and Normalization - page 255

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6.5 Methodlogy of Relational and XML Databases

Interoperability

If a company has both relational database and XML database, it needs coexistence
of both databases to work interoperative together as a cooperative system. This
section offers a stepwise approach to query translation that constructs a gateway
between relational and XML database systems. One of the keys to succeed in migra-
tion strategy is the ability that copes with the changes imposed by business require-
ments. We address the issue of such changes by partitioning the process of database
migration and query translation into three phases as shown in Fig. 6.6 . Phase I is the
translation of the source relational schema into a target XML schema. Phase II is an
inverse mapping that is represented as augmented views. These augmented views
are similar to the relational views but it is more flexible for users to select their root-
based XML documents. Phase III transforms a query from the relational SQL into
an equivalent XQL query over the target XML database. The rationale for defining
phases I and II is that a relational schema is not wholly compatible with an XML