Databases/Introduction/Transwiki Database

Databases are a way of storing data in order that it may be information within a context of both itself and external sources.

Types of Databases

There are several types of databases available [1]:

• Flat Databases
• Relational Databases
• Object Oriented Databases
• Hierarchical Databases
• Post-Relational Databases

Examples of Databases

1. Flat Databases
   • Unix passwd/shadow and group/gshadow files
2. Relational Databases
   • Firebird (http://www.firebirdsql.com/)
   • MySQL (http://www.mysql.com/products/)
   • PostgreSQL (http://www.postgresql.org/)
   • Oracle Database (http://www.oracle.com/database/)
   • Microsoft SQL Server (http://www.microsoft.com/sql/)
3. Post-relational Databases
   • InterSystems Caché (http://www.InterSystems.com)

Database Programming Languages

Many people think that the programming languages used to access a database define what kind of database is used. This is not true.

For example,

SQL can be used to access information in both Relational Databases and in Post Relational Databases.

Caché ObjectScript can be used to access information in Object Oriented Databases, Hierarchical Databases, and Post-Relational Databases.

OQL can be used to access information in Object Oriented Databases.

OCL is part of the UML specification and allows the querying of objects that can be persisted in any form (for example, XML files and relational databases)

MUMPS can be used to access information in Hierarchical Databases, and Flat Databases.

Dbase can be used to access information in Flat Databases.

Database theory is hard to learn and needs an understanding of some mathematical theories to understand certain concepts.

External References

• Borland Presentation on OCL