Flexibility for the End User (the book calls this "More
information from the same amount of data"):
The big advantage of DBMSs is that they provide a
declarative way to specify queries, so that users can quickly specify
the data they want, without specifying how to obtain it. For example,
to obtain the information about the names of the clients that live in
Joe Keogh's properties, an employee could write the following query:
SELECT Client.fName, Client.lName
FROM Client, PrivateOwner, PropertyForRent, Lease
WHERE PrivateOwner.lName = Keogh AND PrivateOwner.fName = Joe
AND PrivateOwner.ownerNo = PropertyForRent.ownerNo
AND PropertyForRent.propertyNo = Lease.propertyNo
AND Lease.clientNo = Client.clientNo
- The DBMS would be responsible for translating the query into a series
of operations for accessing the information and returning it to the user.
- Note that the user only needs to know about the logical organization
of the data. The user does not need to know anything about the physical
organization of the data.
- This means that the user can write the query and immediately
obtain the report, rather than having to place a request with DP
to write a program to create the report.