8. Views of the data

The previous page described how various groups want to see different aspects of a database. This is one of the roles of the RDBMS.

There are three fundamental views and they are useful to different groups of people. It is called the three-level architecture schema.

1. Internal view or physical view

This view exposes all the internal details of how the data is stored on the physical computer. For example the data structures used in memory, the nature of the indexes used for searching, what physical devices are used to store the database and so on.

At this level the operating system is interacting with the database. The kind of person interested in this level of detail would be the engineers putting together the physical equipment and the core designers of the RDBMS itself.

2. Conceptual view

At this level, there is no concern about the physical nature of the database, but rather the concept behind the database. It shows:

• a model of all the information within the database
• the kind of records it holds
• the type of authorisation and validation methods used.

This is the kind of view the database designer is using to set out the whole database

3. External view

This is the view discussed in the previous examples. It sets out what an authorised user can see of the database. It sets out the data they are allowed to see and their authority level to change the records. For example consider a bank database.

Group 1: Customers

A customer needs to enter a PIN, then they can only see their own accounts. They are not allowed to change details such as the account number or to open and close accounts directly

Group 2: Bank teller

They can access any customer accounts (audit trail of course) and can change some of the account details with the permission of a customer. They cannot see the bank's own financial records.

Group 3: Finance staff

These look after the finances of the bank itself, so they may be able to see how many active accounts there are, their type, how much money is in each type and so on. They probably cannot see individual accounts but they can get grouped summary reports.

This is the external view of the database