Three Views (External, Conceptual and Internal) of Data in database.

DBMS is a collection of interrelated files and a set of programs that allow several users to access and modify these files. A major purpose of a database system is to provide users with an abstract view of the data. That is, the system hides certain details of how the data is stored and maintained. However, in order for the system to be usable, data must be retrieved efficiently. The concern for efficiently leads to the design of complex data structure...

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What are Entities and Attributes in a database?

Entities and Attributes: The real world which is being attempted to market on to the database would consist of occasionally a tangible object such as an employee, a component in an inventory or a space or it may be intangible such as an event, a job description, identification numbers or an abstract construct. All such items about which relevant information is stored in the database are called Entities. The qualities of the entity which we store as information are called the attributes. An attribute may be expressed as a numb or as a text. It may...

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What are Data-items in a Database?

Data-items: The term data item is the word for what has traditionally been called the field in data processing and is the smallest unit of data that has meaning to its users. The phrase data element or elementary item is also sometimes used. Although the data item may be treated as a molecule of the database, data items are grouped together to form aggregates described by various names. For example, the data recurred is used to refer to a group of...

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What is audit trail or audit journal in database?

The DBMS has certain routines that maintain audit trail or a journal. An audit trail or a journal is a record of an update operation made on the database. Audit trails may be used to trace the occurrence of an incorrect activity. The audit trail records: Who (user or the application program and a transaction number)When (time and date)Where (location of the user and/or the terminal)What (identification of the data affected, as well as before-and-after image of that portion of the database that was affected by the update operatio...

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What is mandatory access control?

In mandatory access control each data object is tagged or labeled with a certain classification level, and each user is given a certain clearance level. A given data object can then be accessed only by users with the appropriate, clearance. Mandatory schemes are, thus, comparatively rigid. Most DBMS support either discretionary access control or mandatory access control or both. In fact most of the DBMS support discretionary control, and some systems support mandatory control as well, thus, discretionary control is, thus, more likely to be encountered...

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