For Dummies 978-0-470-55741-9 Datasheet download pdf (Page 14)

Part I: Basic Concepts

In the auto dealership example, you can constrain the database to accept

only those four values in the Color column. If a data entry operator then

tries to enter in the Color column a value of, for example, forest green,

the system refuses to accept the entry. Data entry can’t proceed until the

operator enters a valid value into the Color field.

You may wonder what happens when the Curarri AutoWerks decides to

offer a forest-green version of the GT 4000 as a mid-year option. The answer

is (drum roll, please) job security for database-maintenance programmers.

This kind of thing happens all the time and requires updates to the database

structure. Only people who know how to modify the database structure

(such as you) will be able to prevent a major snafu.

The object model challenges

the relational model

The relational model has been fantastically successful in a wide variety of

application areas. However, it does not do everything that anyone would ever

want. The limitations have been made more visible by the rise in popularity

of object-oriented programming languages such as C++, Java, and C#. Such

languages are capable of handling more complex problems than traditional

languages due to their advanced features, such as user-extensible type

systems, encapsulation, inheritance, dynamic binding of methods, complex

and composite objects, and object identity.

I am not going to explain all that jargon in this book (although I do touch on

some of these terms later). Suffice it to say that the classic relational model

doesn’t mesh well with many of these features. As a result, database

management systems based on the object model have been developed and

are available on the market. As yet, their market share is relatively small.

The object-relational model

Database designers, like everyone else, are constantly searching for the

best of all possible worlds. They mused, “Wouldn’t it be great if we could

have the advantages of an object-oriented database system, and still retain

compatibility with the relational system that we have come to know and

love?” This kind of thinking led to the hybrid object-relational model.

Object-relational DBMSs extend the relational model to include support for

object-oriented data modeling. Object-oriented features have been added

to the international SQL standard, allowing relational DBMS vendors to

transform their products into object-relational DBMSs, while retaining

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For Dummies 978-0-470-55741-9 Datasheet Page 14