Many different types of database management systems are available today. Selecting the system that is best suited to meet the objectives of the data management project requires a thorough understanding of the advantages and disadvantages of each.

Relational database. The relational DBMS is the most common and most flexible type of system available today. Basically, data are stored in fields or columns within individual tables. One or more of the fields is considered a key or index field and is used to link multiple tables together. Data tables are linked together by key fields in multiple tables that contain the same information. These links can be one-to-one, many-to-one, or one-tomany (see Key Terms and Concepts chapter).

The primary advantage of a relational system is that common data are stored together in tables that can then be linked together in various ways so data from many different tables can be viewed. Without the relational system, all the data needed for a particular view of the database would have to be stored in the same table (i.e., a flat-file database).

Hierarchical database. This type of database is best represented by the tree or folder structure, common to most computer file storage systems. Starting at the top of the tree, the database splits into multiple branches until the actual data or data files are reached. While an excellent method to store and archive data, this approach is not well suited for dynamic data retrieval and manipulation.

Flat-file database.