A database is a more or less structured collection of data,
stored and managed in some way for a user community to use.
A database can be structured according to a database model, a set
of rules that define the data. In less structured databases the data
is stored more informally.
A collection of flat files is an example of a unstructured
database where at most there could be a naming convention for the
files to indicate the files contents. Spreadsheets have some more
structure in the sense that information in cells can be found using
a cell address. In Excel for instance a unique cell reference is
obtained using the following address format: [workbook]Sheet!Cell. A
further step up in database structure is the use of a simpel
relational database like MS Access. In relational databases data is
stored tables that are interlinked. When these relational links are
enforced the structure of the data becomes more tight. When done
properly a relational database contains data one cannot corrupt.
Database management systems have been developed to manage very
large quantities of data and to provide additional services such as
programming and management environments. Examples are Oracle and SQL
Server. Besides the relational database model there are other models
in use too. In the hierarchical database model data is presented in
tree like structures. In the network model records can participate
in any number of relationships.
SQL*XL software successfully combines the environment of a
less formal data storing environment of MS Excel with capabilities
to interact with RDBMS data stored in high end
database management systems. It combined the flexibility of Excel with
the robustness and data integrity features of the relational database.