DB

 

What is a database? A database is a collection of information that is organized o rganized so that it can easily be accessed, a ccessed, managed, and updated. A database engine may comply with a combination of any of the following: -  The database is a collection of table, files or datasets. -  -  -  -  -  -  - 

Each table is a collection of fields, columns or data items. One or more columns in each table may be selected as the primary key. There may be additional unique keys or non-unique indexes to assist iin n data retrieval. Columns may be fixed length or variable length. Records may be fixed length or variable length. Table and column names may be restricted in length (8, 16 or 32 characters). Table and column names may be case-sensitive.

Advantages

of DBMS?

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Redundancy is controlled.   Unauthorized access is restricted.   Providing multiple user interfaces.

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Enforcing backup integrityand constraints. recovery.

  Providing

Disadvantage in File Processing System?   Data

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redundancy & inconsistency. Difficult in accessing data. Data isolation. Data integrity. Concurrent access is not possible. Security Problems.

Entities  

and

Entity

Sets

An entity is an object that exists and is distinguishable from other objects. For instance, John Harris with S.I.N. 56456-45673-35 56456-45673-35 is an entity, as he can be uniquely identified as one particular person in the universe.   An entity may be concrete (a person or a book, for E.G.) or abstract (like a holiday or a concept).   An entity set is a set of entities of the same type (e.g., all persons having an account at a bank).   An entity can be represented by a set of attributes: o E.g. name, S.I.N., Street, city for ´customerµ entity. o The domain of the attribute is the set of permitted values (e.g. the telephone number must be 10 positive integers). To put in rough term, Entity is an object, about which d data ata can be stored in a d database. atabase.