A database is an organized collection of information or data that can
be displayed by a computer. It is a great form of record keeping. Databases
use tables of data. Three different relationships exist among tables in
A one-to-one relationship allows for one record on a table to be matched
to another single record on a separate table. This type of relationship
is commonly used when security issues are present.
A one-to-many relationship is the most common type of relationship used
in databases. In this case, a record from one table can have multiple
matches from another table. An example of this is a newspaper (one record),
which has many subscribers (multiple records).
This type of relationship is fairly common in professional databases.
Each record on a table can have multiple matches on another table and
vice-versa. In reality, many-to-many relationships can be seen as two
one-to-many relationships with a table linking them together. An example
of this is a newspaper that has many readers, and a reader who reads many
This model illustrates a special type of architecture where there are
three separate processes being run.
- The first tier is the user interface. This can be the client software/web
browser, and is what the user actually sees.
- The second tier is the business logic. This is the bridge between
the client and the database.
- The third tier is the back-end. This is the actual database.
Another important feature of databases are transactions. These can be
described as a set of actions that must be completed on an all or nothing
basis in order to be successful. Online banking is a perfect example of