Object-Relational Databases:Summary

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Summary

• The object-relational data model extends the relational data model by providing a richer type system including collection types, and object orientation.

• Object orientation provides inheritance with subtypes and subtables, as well as object (tuple) references.

• Collection types include nested relations, sets, multisets, and arrays, and the object-relational model permits attributes of a table to be collections.

• The SQL:1999 standard extends the SQL data definition and query language to deal with the new data types and with object orientation.

• We saw a variety of features of the extended data-definition language, as well as the query language, and in particular support for collection-valued attributes, inheritance, and tuple references. Such extensions attempt to pre- serve the relational foundations — in particular, the declarative access to data

— while extending the modeling power.

• Object-relational database systems (that is, database systems based on the object-relation model) provide a convenient migration path for users of relational databases who wish to use object-oriented features.

• We have also outlined the procedural extensions provided by SQL:1999.

• We discussed differences between persistent programming languages and object-relational systems, and mention criteria for choosing between them.

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