Glossary Flashcards
Abstract data type
a conceptual model of how data can be stored and the operations that can be carried out on the data
Abstraction by generalisation/categorisation
the concept of reducing problems by putting similar aspects of a problem into hierarchical categories
Accepting state
the state that identies whether an input string has been accepted. Also known as the goal state
Address bus
used to specify a physical address in memory so that the data bus can access it
Addressable memory
the concept that data and instructions are stored in memory using discrete addresses
Addressing mode
the way in which the operand is interpreted
Adjacency list
a data structure that stores a list of nodes with their adjacent nodes
Adjacency matrix
a data structure set up as a two-dimensional array or grid that shows whether there is an edge between each pair of nodes
Algorithm
a sequence of steps that can be followed to complete a task and that always terminates
Alphabet
the acceptable symbols (characters, numbers) for a given Turing machine
Analysis
the first stage of system development where the problem is identified, researched and alternative solutions proposed
AND
Boolean operation that outputs true if both inputs are true
AND gate
result is true if both inputs are true
Application program interface (API)
a set of subroutines that enable one program to interface with another program
Application software
programs that perform specic tasks that would need doing even if computers didn’t exist, e.g. editing text, carrying out calculations
Arc
a join or relationship between two nodes – also known as an edge
Argument
a value that is passed into a function or subroutine
Arithmetic Logic Unit (ALU)
part of the processor that processes and manipulates data
Arithmetic operation
instructions that perform basic maths such as +, –, /, ×
Array
a set of related data items stored under a single identifier and are accessed based on their position. Can work on one or more dimensions
ASCII
a standard binary coding system for characters and numbers
Assembler
a program that translates a program written in assembly language into machine code
Assembly language
a way of programming using mnemonics
Assignment
the process of giving a value to a variable or constant
Association aggregation
creating an object that contains other objects, which can continue to exist even if the containing object is destroyed
Associative array
a two-dimensional structure containing key/value pairs of data
Asymmetric encryption
where a public and private key are used to encrypt and decrypt data
Asynchronous data transmission
data is transmitted between two devices that do not share a common clock signal
Attribute
a characteristic or piece of information about an entity, which would be stored as a eld in a relational database
Automation
creating a computer model of a real-life situation and putting it into action
Backus-Naur Form (BNF)
a form of notation for describing the syntax used by a programming language
Bandwidth
a measure of the capacity of the channel down which the data is being sent. Measured in hertz (Hz)
Barcode reader
a device that uses lasers or LEDs to read the black and white lines of a barcode
Baudot code
a five-digit character code that predates ASCII and Unicode
Big data
a generic term for large or complex datasets that are difficult to store and analyse
Binary file
stores data as sequences of 0s and 1s
Binary search
a technique for searching data that works by splitting datasets in half repeatedly until the search data is found
Binary tree search
a technique for searching a binary tree that traversed the tree until the search term is found
Binary tree
a structure where each node can only have up to two child nodes attached to it
Bit
a single binary digit from a binary number – either a zero or a one
Bit rate
the rate at which data is actually being transmitted. Measured in bits per second
Bit-mapped graphic
an image made up of individual pixels
Black box testing
using test data to test for an expected outcome
Block
in data storage it is the concept of storing data into set groups of bits and bytes of a xed length
Block interface
code that describes the data being passed from one subroutine to another
BODMAS
a methodology for evaluating mathematical expressions in a particular sequence
Boolean expression
an equation made up of Boolean operations
Boolean operation
a single Boolean function that results in a TRUE or FALSE value
Boundary test data
test data on or close to the boundary of the acceptable range
Branch operations
operations within an instruction set that allow you to move from one part of the program to another
Breadth first
a method for traversing a graph that explores nodes closest to the starting node rst before progressively exploring nodes that are further away
Bubble sort
a technique for putting data in order by repeatedly stepping through an array, comparing adjacent elements and swapping them if necessary until the array is in order
Bus
microscopic parallel wires that transmit data between internal components
Bus topology
a network layout that uses one main data cable as a backbone to transmit data
Bus width
the number of bits that can be sent down a bus in one go
Byte
a group of bits, typically 8, used to represent a single character
Bytecode
an instruction set used for programming that can be executed on any computer using a virtual machine
Cache
a high-speed temporary area of memory
Caesar cipher
a substitution cipher where one character of plaintext is substituted for another, which becomes the ciphertext
Call stack
a special type of stack used to store information about active subroutines and functions within a program
Cardinal number
a number that identies the size of something
Cardinality
the number of elements in a set
Carry bit
used to store a 0 or 1 depending on the result of binary addition
Cartesian product
combining the elements of two or more sets to create a set of ordered pairs
Certification Authority
a trusted organisation that provides digital certicates and signatures
Chaining
a technique for generating a unique index when there is a collision by adding the key/value to a list stored at the same index
Character code
a binary representation of a particular letter, number or special character
Charge coupled device (CCD)
in digital cameras it is a sensor that records the amount of light received and convert it into a digital value
Check digit
a digit added to the end of binary data to check the data is accurate
Checksum
a method of checking the integrity of data by calculating a sum based on the data being sent
Child
a node in a tree that has nodes above it in the hierarchy
Chip
an electronic component contained within a thin slice of silicon
Cipher
an algorithm that encrypts and decrypts data, also known as code
Ciphertext
data that has been encrypted
Circular queue
a FIFO data structure implemented as a ring where the front and rear pointers can wrap around from the end to the start of the array
Class
defines the properties and methods of a group of similar objects
Class diagram
a way of representing the relationship between classes
Client-server
a network methodology where one computer has the main processing power and storage and the other computers act as clients requesting services from the server
Client-server database
a way of implementing a database where the database is put into a server and various users can access it from their workstations. The processing, for example, running a query, will take place on the server
Client-server model
a way of implementing a connection between computers where one computer (the client) makes use of resources of another computer (the server)
Clock
a device that generates a signal used to synchronise the components of a computer
Clustering
when a hashing algorithm produces indices that are not randomly distributed
Code of conduct
a voluntary set of rules that dene the way in which individuals and organisations will behave
Codomain
all the values that may be output from a mathematical function
Collision
when a hashing algorithm produces the same index for two or more different keys
Colour depth
the number of bits or bytes allocated to represent the colour of a pixel in a bit-mapped graphic
Commitment ordering
a technique to ensure concurrent transactions on a shared database are executed based on the timestamp of when the request is made and also the precedence the request takes over other simultaneous request
Compiler
a program that translates a high-level language into machine code by translating all of the code
Complementary metal oxide semiconductor (CMOS)
is an alternative technology that performs the same functions as a CCD
Components
the values within a vector
Composition
building up a whole system from smaller units. The opposite of decomposition
Composition aggregation
creating an object that contains other objects, and will cease to exist if the containing object is destroyed
Compression
the process of reducing the size of a le
Computational hardness
the degree of difculty in cracking a cipher
Computational security
a concept of how secure data encryption is
Concurrence
the concept of two users trying to access the same data item at the same time
Constant
an item of data whose value does not change
Constant time
in Big O notation where the time taken to run an algorithm does not vary with the input size
Context-free language
an unambiguous way of describing the syntax of a language useful where the language is complex
Control bus
controls the ow of data between the processor and other parts of the computer
Control unit
part of the processor that manages the execution of instructions
Controller
in SSDs a controller is needed to organise data into blocks for storage purposes
Convex combinations
a method of multiplying vectors that produces a resulting vector within the convex hull
Convex hull
a spatial representation of the vector space between two vectors
Copyright
the legal ownership that applies to software, music, lms and other content
Countable set
a finite set where the elements can be counted using natural numbers
Countably infinite sets
sets where the elements can be put into a one-to-one correspondence with the set of natural numbers
CRUD
an acronym that explains the main functions of a database: Create, Read, Update, Delete
Cultural issues
factors that have an impact on the ways in which we function as a society
Current Instruction Register (CIR)
register that stores the instructions that the CPU is currently decoding/executing
Data abstraction
hiding how data is represented so that it is easier to build a new kind of data object, e.g. building a stack from an array
Data Bus
transfers data between the processor and memory
Data Dictionary
a list of all the data being used in the system including name, length, data type and validation
Data flow diagram (DFD)
a visual method of showing how data passes around a system
Data misuse
using data for purposes other than for which it was collected
Data Structure
a common format for storing large volumes of related data, which is an implementation of an abstract data type
Data transfer operation
operations within an instruction set that move data around between the registers and memory
Data type
determines what sort of data is being stored, e.g. integer, real, and how it will be handled by the program
Database management system
software that enables the management of all aspects of a database including adding, updating and querying the data
De Morgan’s Law
a process for simplifying Boolean expressions
Debug
the process of finding and correcting errors in programs
Declaration
the process of defining variables and constants in terms if their name and data type
Declarative Language
languages that declare or specify what properties a result should have, e.g. results will be based on functions
Decomposition
breaking down a large task into a series of subtasks
Decryption
the process of deciphering encrypted data or messages
Definite iteration
a process that repeats a set number of times
Depth first
a method for traversing a graph that starts at a chosen node and explores as far as possible along each branch away from the starting node before backtracking
Design
the second stage of system development where the algorithms, data and interface are designed
Dictionary (data structure)
a data structure that maps keys to data
Dictionary-based encoding
a method of compressing text files
Difference
describes which elements differ when two sets are joined together
Digital camera
a device for creating digital images of photographs, which can be printed or transferred onto a computer to be manipulated and stored
Digital certificate
a method of ensuring that an encrypted message is from a trusted source as they have a certificate from a Certification Authority
Digital signature
a method of ensuring that an encrypted message is from a trusted source as they have a unique encrypted signature verified by a Certificate Authority
Direct address
the operand is the datum
Directed graph
a graph where the relationship between nodes is one-way
Direction
one of the two components of a vector
Distributed processing/computing
the principle of spreading large and complex tasks over a number of computers or servers
Distributed Program
a program specifically written to be used in a distributed processing environment
Domain
all the values that may be input to a mathematical function
Domain name
the recognisable name of a domain on the Internet
Domain name server (DNS)
a server that contains domain names and associated IP addresses
Domain name server (DNS) system
a system of connected domain name servers that provides the IP address of every website on the Internet
Dot product
multiplying two vectors together to produce another vector
Dry run
the process of stepping through each line of code to see what will happen before the program is run
Dynamic data structure
a method of storing data where the amount of data stored (and memory used to store it) will vary as the program is being run
Dynamic Host Configuration Protocol (DHCP)
a set of rules for allocating locally unique IP addresses to devices as they connect to a network
Edge (programming)
a connection between two nodes in a graph or tree structure - also known as an arc
Edge
in a database graph schema, it refers to the link and relationship between two nodes
Element
a single value within a set or list - also called a member
Email server
a dedicated computer on a network for handling email
Empty list
a list with no elements in it
Empty set
the set that contains no values
Encapsulation
the concept of putting properties, methods and data in one object
Encryption
the process of turning plaintext into scrambled ciphertext, which can only be understood if it is decrypted
Entity
an object about which data will be stored
Entity identifier
an attribute which can uniquely identify each instance of an entity
Entity relationship diagram
a visual method of describing relationships between entities
Erroneous test data
test data that is clearly incorrect and should produce an error
Ethical issues
factors that define the set of moral values by which society functions
Evaluation
the final stage of system development where the system is judged according to certain criteria
Event
something that happens when a program is being run
Exception handling
the process of dealing with events that cause the current subroutine to stop
Exponent
the ‘power of’ part of a number indicating how far a binary point should be shifted left or right
Exponent time
in Big O notation where the time taken to run an algorithm increases as an exponential function of the number of inputs. For example, for each additional input the time taken might double
Factorial
the product of all positive integers less than or equal to n
Feasibility study
an analysis of whether it is possible or desirable to create a system
Fetch-execute cycle
the continuous process carried out by the processor when running programs
Field
an item of data
FIFO
first in first out refers to a data structure such as a queue where the first item of data entered is the first item of data to leave
File
a collection of related data
File management
how an operating system stores and retrieves files
Filter function
a method of creating a subset based on specified criteria
Finite
countable
Finite set
a set where the elements can be counted using natural numbers up to a particular number
Finite state machine (FSM)
any device that stores its current status and whose status can change as the result of an input. Mainly used as a conceptual model for designing and describing systems
Firewall
hardware or software for protecting against unauthorised access to a network
First-class object
any object that can be used as an argument or result of a function call
Fixed point
wheer the decimal/binary point can move within a number
