Programming the Perl DBI

The Relational Database Methodology

The relational database model revolves around data storage units called tables, which have a number of attributes associated with them, called columns. For example, we might wish to store the name of the megalithic site, its location, what sort of site it is, and where it can be found on the map in our megaliths table. Each of these items of data would be a separate column.

In most large database systems, tables are created within containing structures known as schemas . A schema is a collection of logical data structures, or schema objects, such as tables and views. In some databases, a schema corresponds to a user created within the database. In others, it’s a more general way of grouping related tables. For example, in our megalithic database, using Oracle, we have created a user called stones. Within the stones user’s schema, the various tables that compose the megalithic database have been created.

Data is stored within a table in the form of rows . That is, the data for one site is stored within one row that contains the appropriate values for each column. This sort of data layout corresponds exactly to the row-column metaphor used by spreadsheets, ledgers, or even plain old tabulated lists you might scribble in a notepad.

An example of such a list containing megalithic data is:

Site Location Type Map Reference ---- -------- ---- ------------- Callanish I Western Isles Stone Circle and Rows NB 213 330 Stonehenge Wiltshire Stone Circle and ...