DATABASE MANAGEMENT SYSTEM

Database

A shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.

System catalog (data dictionary or metadata) provides the description of the data to enable program–data independence.

Logically related data comprises entities, attributes, and relationships of an organization's information.


Database Approach
Data definition language (DDL).
– Permits specification of data types, structures and any data constraints. All specifications are stored in the database.

Data manipulation language (DML).
– General enquiry facility (query language) of the data.

Controlled access to database may include:
– A security system.
– An integrity system.
– A concurrency control system.
– A recovery control system.
– A user-accessible catalog.

A view mechanism.
– Provides users with only the data they want or need to use.

Database Uses

• Providing knowledgeable customer service
• Make products and services tailored to customer preferences
• Develop individualized, targeted marketing programs
• Conduct one-on-one dialogs with each customer
• Enlisting loyal customers in referral programs
• Classify customers by interests and profitability so as to give special attention to those most likely to build the bottom line
• Devise effective marketing programs to new prospects




File-based Systems

A collection of application programs that perform services for the end users (e.g. reports).

Each program defines and manages its own data.


Common Problems of File-based Approach

Separation and isolation of data
– Each program maintains its own set of data. Users of one program may be unaware of potentially useful data held by other programs.

Duplication of data
– Same data is held by different programs. Wasted space and potentially different values and/or different formats for the same item.


Data dependence
– File structure is defined in the program code.

Incompatible file formats
– Programs are written in different languages, and so cannot easily access each others files.

Fixed Queries/Proliferation of application programs
– Programs are written to satisfy particular functions. Any new requirement needs a new program.
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Database Management System (DBMS)

A software system that enables users to define, create, and maintain the database and which provides controlled access to this database.




Typical Functions of DBMS

a) The ability to update and retrieve data

This is a fundamental component of a DBMS and essential to database management. Without the ability to view or manipulate data, there would be no point to using a database system.

Updating data in a database includes adding new records, deleting existing records and changing information within a record. The user does not need to be aware of how DBMS structures this data, all the user needs to be aware of is the availability of updating and/or pulling up information, the DBMS handles the processes and the structure of the data on a disk.

b) Support Concurrent Updates

Concurrent updates occur when multiple users make updates to the database simultaneously. Supporting concurrent updates is also crucial to database management as this component ensures that updates are made correctly and the end result is accurate. Without DBMS intervention, important data could be lost and/or inaccurate data stored.

DBMS uses features to support concurrent updates such as batch processing, locking, two-phase locking, and time stamping to help make certain that updates are done accurately. Again, the user is not aware all this is happening as it is the database management system's responsibility to make sure all updates are stored properly.

c) Recovery of Data
In the event a catastrophe occurs, DBMS must provide ways to recover a database so that data is not permanently lost. There are times computers may crash, a fire or other natural disaster may occur, or a user may enter incorrect information invalidating or making records inconsistent.

If the database is destroyed or damaged in any way, the DBMS must be able to recover the correct state of the database, and this process is called Recovery. The easiest way to do this is to make regular backups of information. This can be done at a set structured time so in the event a disaster occurs, the database can be restored to the state that it was last at prior to backup.

Components of DBMS Environment

Hardware
– Can range from a PC to a network of computers.

Software
– DBMS, operating system, network software (if necessary) and also the application programs.

Data
– Used by the organization and a description of this data called the schema.

Procedures
– Instructions and rules that should be applied to the design and use of the database and DBMS.
People


Personnel involved in the Database Environment

Data Administrator (DA)
Database Administrator (DBA)
Database Designers (Logical and Physical)
Application Programmers
End Users (native and sophisticated)


History of Database Systems

First-generation
– Hierarchical and Network

Second generation
– Relational

Third generation
– Extended Relational
– Object-Oriented

Advantages of DBMS

Control of data redundancy.
Data consistency
More information from the same amount of data.
Sharing of data.
Improved data integrity.
Improved security.
Enforcement of standards.
Economy of scale.
Balanced conflicting requirements
Improved data accessibility and responsiveness
Increased productivity
Improved maintenance through data independence
Increased concurrency
Improved backup and recovery services


Disadvantages of DBMS

Complexity
Size
Cost of DBMS
Additional hardware costs
Cost of conversion
Performance
Higher impact of a failure

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