Computing F452: Data Types

Key terms on the Data Types unit of F452

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Data Type
The kind of data being stored by a variable or field. A form of validation as it limits the value which can be stored. E.g. String, Real and Boolean
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Integer
Any whole number. Can be unsigned (only positive) or signed (negative or positive). Typical size 2 or 4 bytes
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Real Number
A number which can be represented with a fractional part. Usually in the form of Float and Double. Typical size 4 or 8 bytes
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String
Used to store any textual data which include letters, numbers, symbols and punctuation. Typical size 1 byte per character
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Character
A data type that stores a single textual character. Typical size 1 byte
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Boolean
Can only store True or False values. Typical size 1 byte
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Date
Used to represent date and times. Typical size 4 or 8 bytes
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Array
A set of data items of the same type grouped together using a single identifier. May have many dimensions and are organised in tables
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Array Element
Each individual data held within an array. Each is address using the arrays identifier and index location
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Byte
A group of 8 bits
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Kilobyte
1024 bytes
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Records
Collection of data items grouped together. Each item can be different data types. Each collection refers to a particular individual or object in real life
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Field
A data item stored as part of a record. Usually given a data type
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File
Data stored in a separate file and accessed by the program. The file structure describes the order in which data is stored, how the data is split and how each item is found
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Serial File
Data is stored in the order in which they were added to the file. To find a particular record the program must read through every record until it is found. If the record is not there the program will not know until the end of the file is reached.
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Sequential File
Records are stored in order using a key field. Records can be found by searching the key field. If the file doesn't exist it'll know as soon as the logical location of the key is passed. Adding new files requires recreating the file to keep the order
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Serial File Access
Records are read, one at a time, from the physical start of file, in the order in which they are stored
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Sequential File Access
Records are read, one at a time in key value order, from the logical start of the file. Items are processed in a known, predictable, order making large amounts of data easier to process.
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Direct Access FIle
Records can be retrieved immediately, provided its position in the file is known. This often means that items must have a known length so that the program can calculate where in the file the record is located.
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Indexed Access
Uses additional files that contain information about the location of each record. The index is searched first to find the location of the record.
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Indexed Sequential File Access
Uses additional Index files containing indexes to the records in a sequential file. Allows sequential and indexed approaches to be used. Index searched to find the section of the file where the record maybe and then sequential search used from there
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File Operations
Actions that can be performed on an existing data file. Includes Reading, Writing, Updating, Inserting, Appending and Overwriting
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File Locking
Used to prevent the contents of data files being changed if it's already being used. This includes Read-Only Access (self explanatory), Record Locking (prevents access to record being updated), Field Locking (prevents access to field being updated)
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Estimating File Size
Determine maximum size of each field, add each together, multiply by the number of records and add 10% for overheads then convert into sensible unit (GB/KB/MB...)
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Other cards in this set

Card 2

Front

Any whole number. Can be unsigned (only positive) or signed (negative or positive). Typical size 2 or 4 bytes

Back

Integer

Card 3

Front

A number which can be represented with a fractional part. Usually in the form of Float and Double. Typical size 4 or 8 bytes

Back

Preview of the back of card 3

Card 4

Front

Used to store any textual data which include letters, numbers, symbols and punctuation. Typical size 1 byte per character

Back

Preview of the back of card 4

Card 5

Front

A data type that stores a single textual character. Typical size 1 byte

Back

Preview of the back of card 5
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