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Unformatted text preview: ook from the
members data table, and the 'Book No.' field to cross-reference the book's details
of each overdue book from the books data table. The final report thus produced
would look something like the one shown in Figure 16.10.
The relational database model provides greater flexibility of data organization and
future enhancements in the database as compared to the hierarchical and network
database models. For many applications, the data elements can be organized in the
relational database model in a manner that is identical to the actual relationships
that exist between the data elements. Hence many users find the relational
database model to be closer to their intuitive model of the real-life situation,
making this model easier to understand and use. Moreover, if new data is to be
added to an existing relational database, it is not necessary to redesign the database
afresh. Rather, new tables containing the new data can be added to the database,
and then these tables can be related to the existing tables through the use of
common key fields. Data can also be reorganized when necessary to create new
tables by selecting certain rows or specific columns from other tables, or by
joining columns and rows from two separate tables.
Object-oriented Databases The hierarchical, network, and relational database models (henceforth referred to
as conventional database models) were developed for the conventional business
data processing applications, such as inventory control, payroll, accounts,
employee information systems, and so on. Attempts to make use of these database
models in a wide variety of other types of applications exposed several serious
shortcomings of these database models. These applications include computeraided design (CAD), computer-aided engineering (CAE), computer-aided
manufacturing (CAM), computer-aided software engineering (CASE), expert
systems, and multimedia systems, which deal with documents having text,
graphics, animation, audio, and video. Some of the key features required for
effective modeling of these applications that are absent in conventional database
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This document was uploaded on 04/07/2014.
- Spring '14