Key Definitions Flashcards
Flat File
A set of single tables with no links between them.
(Relational)
database
A set of related tables with links between them
Primary key
A field or combination of fields that uniquely identify a record in a table
Foreign key
A field that appears in a table that is the primary key of another table and is used to form a link between
the two tables.
Indexes
database
Indexes are separate data structures that are set up to improve access time to records
First normal form
This is a database where tables contain no repeating attributes or repeating groups of attributes.
Second normal
form
This is a database where tables contain no repeating
attributes or repeating groups of attributes and no partial dependencies.
Third normal form
This is a database where tables contain no repeating
attributes or repeating groups of attributes, no partial dependencies and no transitive dependencies.
Redundant Data
Data that is stored repeatedly
Inconsistent Data
Multiple copies of data which are supposed to be the same but are in fact different
Algorithm
A finite set of instructions designed to solve a specific task
Procedure
A set of program instructions which perform a specific
task and can be called by another program.
Parameter
A variable that can be passed to or from a procedure
Passing by
reference
The address of the variable is passed to the
procedure.
Passing by Value
A local copy of the variable is created for the procedure and discarded afterwards.
Recursive
Algorithm
An algorithm that calls itself and has a base case to allow it to terminate.
Database
Management
System
A piece of software which controls access to the data in a database, acting as an interface between the data and the application programs.
Data inconsistency
When two copies of the same data items (redundant
data) are supposed to be the same but aren’t e.g. if one has been updated and the other hasn’t
Data Redundancy
When the same data is stored more than once.
Program-data
dependence
When the structure of the data within a program is defined as part of the program
Program-data
independence
When data is separate from the programs that use that data
Data Dictionary
Holds data about the database
Database
administrator
A database administrator is the person in a company who is responsible for the structure, security and management of the database system and the data in it.
Record Locking
A process to prevent access by others to a record while it is being updated
Data Warehouse
A large collection of data collected together from a variety of locations for efficient analysis.
Data Mining
The analysis of a large amount of data in a data
warehouse to provide new information such as
analysing trends to find previously undiscovered
relationships
Distributed
systems
Data is be stored on different computers to maximise efficiency and the processing is shared by the different computers to allow processing to be carried out quickly and more complex processing to be possible
Data Structure
A group of related data items which can be managed as a single set.
Queue
A first-in first-out data structure where items are added at the end and removed from the front.
Stack
A last-in first-out data structure where items are added and removed from the same end
Linked List
A set of data elements, where each element contains
the data itself
a pointer to the next element
Array
A set of data items of the same data type grouped
together using a single identifier. Each element can be accessed by the name and the subscript.
Record
A complete collection of data items relating to a single person or thing of interest which is treated as a single unit for processing. It is suitable for data when there
are different data types.
Text-based
interface
Input to the computer is typed usually by via a
command prompt
Graphical User
Interface
An interface where most communication is via screen elements such as windows, icons, menus, pointers etc
Forms Dialogue
Computer prompts for input into specific fields on a screen dialogue form
Speech
recognition
Command and/or text input are given by human speech
Sound synthesis
The production of sounds resembling human speech by electronic methods
Hand-writing
recognition
User ‘writes’ on a touch screen using a stylus, the handwriting is analysed, compared with samples already stored in the computer and converted into characters which are then stored in digital editable format on the computer
Dedicated Key
This is a keystroke or a combination of keystrokes that can carry out a particular task. An example would be Ctrl-B to make some text bold
Soft key
A soft key is a software key which can be assigned a specific function so that when it is pressed it carries out that function.
Pointing Device
A device that allows the user to control and provide data to the computer using physical gestures - the
movement of the device is echoed by movements of the cursor around the screen, and the user can use
the buttons on the device to move objects around the screen, select menu options, select icons, etc.
Sign and
Magnitude
The most significant bit represents the sign (0 for +ve and 1 for –ve). The remaining bits give the magnitude of the number.
Hexadecimal
Representation
Group the bits into groups of 4 (from the right) and convert each group to hexadecimal representation
Twos complement
representation
The most significant bit is weighted a usual but represents the negative of that number. If the most significant bit is a 1, the number if negative. It is found by reversing the bits and adding 1 or by writing down all the bits from the right until the first 1, writing that down and then reversing the rest.
Floating Point
Format
The number is stored in two parts a. The Mantissa (the magnitude) b. The exponent (the power of 2 that multiplies the mantissa) FPF numbers always begin 01 or 10.
Truncation
When a number is truncated to a certain number of decimal the least significant digits beyond that number of places are omitted. The number is approximated to the whole number, tenth, hundredth etc nearer zero.
e.g. 26.76 is truncated to 26.7
Rounding
When a number is round to a certain number of decimal places it is approximated to the nearest whole number, tenth, hundredth etc.
e.g. 26.76 is rounded to 26.8
Overflow
Occurs when the result of a computation is too large to be represented in the system
Underflow
Occurs when an answer is too close to zero to be represented satisfactorily by the computer
Logical Shift Left
A logical shift left causes the most significant bit to be shifted into the carry bit and a zero moved into the vacant space.
Each left shift multiplies the number by 2
Logical Shift Right
A logical shift right causes the least significant bit to be shifted into the carry bit and a zero moved into the vacant space.
If the number is negative, the sign is not preserved
Arithmetic Shift
Left
An arithmetic shift left causes the most significant bit to be shifted into the carry bit and a zero moved into the vacant space.
The effect of an arithmetic shift left by one space is to multiply the number by 2 (2 places multiplies by 4 etc
Arithmetic Shift
Right
An arithmetic shift right causes the least significant bit to be shifted into the carry bit. To preserve the numerical value of the number, the vacant space is filled by whatever is in the sign bit. (1 if negative, 0 if
positive).
The effect of an arithmetic shift right by one place is to divide the number by 2. (Ignoring remainders)
Standard
Character sets
These allow computers to communicate as the binary strings will be interpreted the same way by different systems. An example is ASCII.
NOT
Gives 1 if 0 and 0 if 1.