Database Management Systems

Database Management Systems  (DBMSs)  are software systems providing a way of defining and manipulating data models, storing data, allowing controlled access to the data (Gibbon et al., 1997a, Appendix H). Especially for larger amounts of data a formal data model (a description of possible entities and their relation to each other) has to be defined and managed. Without a data model the storage of large amounts of data on a computer is very unlikely to be well-structured and it is not easy to access. Additionally, the data input cannot be evaluated automatically, which may lead to corrupted data.

Most commonly used DBMSs are relational data bases, represented by software such as Microsoft Access, Oracle, Lotus Approach, Borland dBase, etc. A standard language for relational databases is the Structured Query Language (SQL) which is also standardised by ISO (ISO/IEC 9075-3:1995, 1995; ISO/IEC 9075-4:1996, 1996; ISO/IEC 9075:1992, 1992; ISO/IEC DIS 9075-1, 1999).

In relational databases information is stored in tables which are related to each other by unique identifiers, the primary key. By means of this key pieces of information related to each other can be located and processed.

Other database types are hierarchical models or networks. They have the advantage of enabling hierarchies of data inputs, but the functionality of searching for specified data is limited. Network data models, for example, need certain `entry points' to start from; other possibilities of obtaining data do not exist, navigation is only possible from the defined starting points.

A fairly new approach is promising: Using the functionality of object-oriented programming languages (OOP, such as C++),   object-oriented data bases (OODB) provide a lot of functionalities of OOPs. Data records, in relational databases stored in a table, are seen as objects. In OODB it is easier to define hierarchies than in relational databases.

Thorsten Trippel
Fri May 21 13:04:11 MET DST 1999