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Database Terminology (I)


Byte
- It is conventionally 8 bits
- Smallest individually addressable group of bits

Data Item
- Smallest unit of named data
- Also referred to as field or data element
- May consist of any number of bits or bytes
- Eg., Last name, First name, DoB, Soc Sec Num

Data
- Values taken by various data items
- Facts, Numbers, Letters, Symbols related to an object, an idea or a condition

Data Aggregate
- Collection of data items referred to as a whole with a given name
- Eg., DATE item that consists of mm, yy and dd

Record
- A collection of data items and/or data aggregates

Logical Data Description
- Is the manner in which data are presented to the application programmer or user of the data

Physical Data Description
- is hte manner in which data are recorded physically on the storage medium

Logical Record
- is a set of data items and /or data aggregates which the user or application programmer specifies

Physical Record
- A physical record could contain more than one logical records in order to save storage space or improve access time
- Basic unit of data which is read or written by a single input/output command to the computer

Block
- is a group of data that composes a physical record

File
- is a named collection of all occurrences of a given type of logical record

Extent
- is a collection of physical records that are contiguous in secondary storage

Simple File
- is a file where every logical record has the same number of data items

Complex Files
- are those in which records may have a varying number of data items because of the existence of repeating groups


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