Purpose of Database Systems

Purpose of Database Systems

1.  To see why database management systems are necessary, let's look at a typical ``file-processing system'' supported by a conventional operating system.

The application is a savings bank:

o  Savings account and customer records are kept in permanent system files.

o       Application programs are written to manipulate files to perform the following tasks:

^§        Debit or credit an account.

^§        Add a new account.

^§        Find an account balance.

^§        Generate monthly statements.

2.     Development of the system proceeds as follows:

o       New application programs must be written as the need arises.

o  New permanent files are created as required.

o  but over a long period of time files may be in different formats, and

o       Application programs may be in different languages.

3.     So we can see there are problems with the straight file-processing approach:

o       Data redundancy and inconsistency

^§        Same information may be duplicated in several places.

^§        All copies may not be updated properly.

o       Difficulty in accessing data

^§        May have to write a new application program to satisfy an unusual request.

^§        E.g. find all customers with the same postal code.

^§        Could generate this data manually, but a long job...

o       Data isolation

^§        Data in different files.

^§        Data in different formats.

^§        Difficult to write new application programs.

o       Multiple users

^§        Want concurrency for faster response time.

^§        Need protection for concurrent updates.^

^§        E.g. two customers withdrawing funds from the same account at the same time - account has $500 in it, and they withdraw $100 and $50.

The result could be $350, $400 or $450 if no protection.

o       Security problems

^§        Every user of the system should be able to access only the data they are permitted to see.

^§        E.g. payroll people only handle employee records, and cannot see customer accounts; tellers only access account data and cannot see  payroll data.

^§        Difficult to enforce this with application programs.

o       Integrity problems

^§        Data may be required to satisfy constraints.

^§        E.g. no account balance below $25.00.

^§        Again, difficult to enforce or to change constraints with the file-

processing approach.

These problems and others led to the development of database management systems.

4.  To see why database management systems are necessary, let's look at a typical ``file-processing system'' supported by a conventional operating system.

The application is a savings bank:

o  Savings account and customer records are kept in permanent system files.

o       Application programs are written to manipulate files to perform the following tasks:

^§       Debit or credit an account.

^§       Add a new account.

^§       Find an account balance.

^§       Generate monthly statements.

5.     Development of the system proceeds as follows:

o       New application programs must be written as the need arises.

o  New permanent files are created as required.

o  but over a long period of time files may be in different formats, and

o       Application programs may be in different languages.

6.     So we can see there are problems with the straight file-processing approach:

o       Data redundancy and

^§        Same information may be duplicated in several places.

^§        All copies may not be updated properly.

o       Difficulty in accessing data

^§        May have to write a new application program to satisfy an unusual request.

^§        E.g. find all customers with the same postal code.

^§        Could generate this data manually, but a long job...

o       Data isolation

^§        Data in different files.

^§        Data in different formats.

^§        Difficult to write new application programs.

o       Multiple users

^§        Want concurrency for faster response time.

^§        Need protection for concurrent updates.

^§        E.g. two customers withdrawing funds from the same account at the same time - account has $500 in it, and they withdraw $100 and $50.

The result could be $350, $400 or $450 if no protection.

o       Security problems

^§        Every user of the system should be able to access only the data they are permitted to see.

^§        E.g. payroll people only handle employee records, and cannot see customer accounts; tellers only access account data and cannot see

payroll data.

^§        Difficult to enforce this with application programs.

o       Integrity problems

^§        Data may be required to satisfy constraints.

^§        E.g. no account balance below $25.00.

^§        Again, difficult to enforce or to change constraints with the file-

processing approach.

These problems and others led to the development of database management systems.