4ff82DBMS2 (2)

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Amity Business School

Characteristics of DBMS• Query processing and optimisation• Transaction management• Database recovery• Database security and authorisation• Distributed databases• Data warehousing and data mining

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Advantages • Program-data independence•

Minimal data redundancy• Improved data consistency• Improved data sharing• Increased productivity of application development• Enforcement of standards• Improved data quality• Improved data accessibility and responsiveness• Reduced program maintenance

Database Approach

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• The separation of data descriptions (metadata)from the application programs that use the data.

In the database approach data descriptions arestored in a central location called the datadictionary. This property allows an organisation’sdata to change and evolve (within limits) withoutchanging the application program that processthe data.

Program-Data Independence

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• Data files are integrated into a single, logical structure.

Each primary fact is recorded (ideally) in only one placein the database.E.g. Employee data not with the payroll and benefit files. Note: Data redundancy is not eliminated entirely. Some data

items will appear in more than one place (e.g. employeeno.) to represent the relationship with others.

Minimal Data Redundancy

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• By eliminating (or controlling) dataredundancy, we greatly reduce the

opportunities for inconsistency.E.g. employee address is stored only once and

hence we cannot have disagreement on thestored values.

• Also, updating data values is greatlysimplified and have avoid the wasted storagespace.

Improved Data Consistency

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• A database is designed as a shared corporateresource. Authorised users are grantedpermission to use the database, and each user(or group of users) is provided one or moreuser views to facilitate this use.

E.g. employee data common to payroll, benefitapplications will be shared among differentusers.

Improved Data Sharing

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• A major advantage of the database approach is that it

greatly reduces the cost and time for developing newbusiness applications. – Programmer could concentrate on the specific

functions required for the new application,without having to worry about design or low-levelimplementation details; as related data havealready been designed and implemented.

Increased Productivity of Application Development

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– DBMS provides a number of high-levelproductivity tools such as forms and reportgenerations and high-level languages thatautomate some of the activities of databasedesign and implementation.

Increased Productivity ofApplication Development contd.

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– When the database approach is implemented with fullmanagement support, the database administrationfunction should be granted single-point authority andresponsibility for establishing and enforcing datastandards.

– Standards include naming conventions, data qualitystandards and uniform procedures for accessing,

updating and protecting data. – Powerful set of tools for developing and enforcing these

standards are available for some DBMS.

Enforcement of Standards

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With relational database, end users without programmingexperience can often retrieve and display data, evenwhen it crosses traditional departmental boundaries.

– English-like query language SQL and query tools such as

Query-By-Example provide such facilities.

Improved Data Accessibilityand Responsiveness

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Stored data are changed frequently for variety of reasons such as new data items types are added,and data formats change (e.g. date format fromtwo-digit to four digit).

Data independence allows to reduce the programmaintenance time.

Reduced Program Maintenance

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Disadvantages • DBMS are more vulnerable than file-based

system because of the centralised nature of alarge integrated database.

• If a failure occurs the recovery process is morecomplex and some times may results in losttransactions.

• Hardware, software and personnel cost arehigher for DBMS.

Database Approach

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