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AQA Computing A2

Deffinitions

TermDefinition
abstract data type a data type those properties are inderpendant of any programing language
abstraction unnessercerry details in a system are removed to make a model.
absolute error the difference between the actual number and the represented number
aggregation same as containment
Ajax a web topology that allows only the part of a eb page that needs refreshing to be reloaded.
algorithm a sequence of unambigious instructions for solving a problem
API a layer of software that allows applications to call on the services of the operating system. Used to developers
asynchronous serial data transmission the arrival of data can't be predicted by the reciever. The start bit is used as a signal to temporarilly synchronise the reciever and transmitter
attribute a property or characteristic of an entity
attributes a properity of an object
automation turning an abstraction into a form that can be proccesed by a computer
bandwidth "for a transmission medium
base case a value that has no refference to the general case
baseband system a single data channel in which the whole bandwidth of the transmittion medium is dedicated to one transmission
baud rate the rate at which signals on a wire may change
bit rate the number of bits transmitted a second. (in serial transmission this is the same as the baud rate)
Bluetooth a wireless protocol for exchanging data over a short distance. Uses FHSS- data chopped into chunks and sent on separate frequencies
BNF a notation for expressing the rules for constructing valid strings in regular language
Breath first tree traversal every node on a level is visited before exploring other levels
broadband system bandwidth of a data channel can carry many streams at the same time
buble sort during a pass through the list naboring values are swapped if they are not in order. Several passes are required to fully order the list
cancelation error a loss of accuracy due to adding a large number to a small one. The result is just the large number
cipher text an encrypted message
circular queue when the last element in an array is being used the next element joins the beginning of the array
Class definition a pattern or template used to create objects
client- server system a system where clients request services provided by servers
common gateway interface a gateway between the webserver and the webserver extension. it tells the server how to send information and how to deal with the reply.
complexity the worst case of the most efficient solution to a problem
communication protocol a set of pre-arranged rules used to ensure succsessful data exchange.
composite key a combination of attributes used to make up a primary key
conceptual model a representation of the datbase requirements
containment objects are made up of smaller objects. Also called aggregation
cryptography the science of designing ciphers
crytanalysis trying to turn cipher text into plain text without knowing the key
data transmission movement of data from one place to another
database a structured collection of data
decision problem has output yes or no
dedth first tree traversal nodes are visited across many levels first
desktop operating system an operating system that can carry out a large range of general purpose tasks
dynamic allocation memory space is allocated when required
dynamic webpage content content that is generated when the request is recieved.
embedded computer system a dedicated computer system with limited or non-existant user interface.
Encapsulation data in an object is hidden from other objects
encryption using an algorithm and a key to convert message data into a form that is not understandable without the key
entities components that make up a system
entity "an object
equivilent turing machine all other programs can be reduced to turing machines.
floating point notation "a real number represented by a sign
foreign key an attribute in one table that is a primary key in another
FSA an FSM that produces no outputs but instead responds true or false when finnished
FSM a set of input symbols that are prosessed by using a finite set of states and transissions between them
gateway a device used to connect networks using different protocols
general case the solution in terms of int's self for a value n
graph diagram consisting of nodes and edges.
Halting problem "is it possible
Halting state a state that has no on going tranission
handshaking protocol the sending and receiving devices exchange signals to ensure that the other device is ready to receive
heap the memory locations availible to applications for dynamic allocation
Heuristic using expert knowledge to guess at a solution to an intractable problem
In- order tree traversal "Left
inheritance "a class is used to define a hierarchy of subclasses
interactive operating system the user and the computer are in direct 2 way communication
internet a collection of LANS that are connected via WANs
intractable a problem with no reasonable time solution
linear queue elements join the queue at one end and leave at the other.
linear search "starts at the beginning of a list an works to the end
list a collection of elements with an inherant order
local area network linked computers in close proximity
memory leakage memory locations that are no longer required are not returned to the stack. Eventually no memory is left on the heap
model an abstraction of an entity in the real world to enable an automated solution
Moores machine an FSM that outputs from states not during transissions
Mealy machine an FSM that produces outputs based on the state and inputs (outputs given on transissions)
network operating system a layer of software is added to the operating system that allows transparent interaction to other computers.
network segment a run of ethernet cable to which a number of workstations are connected
nomalisation optimising a database to remove redundant data
non-computable a problem with no algorithmic solution
Non-deterministic FSM a FSM that has more than 1 possible path for 1 set of inputs
normalisation a method of maximising presicion and range
null pointer a pointer that does not point to anything. Usally 0 or -1
Big O notation a method for representing the complexity of a problem.
Object An instance of a class
orerating system the most fundermental system program. Designed to hide the complexities or hardware and manage resources
overflow the value is too large to be represented by the number of bits availible
parallel data tranmission bits are sent down several wires simultaniously
peer-to-peer network a network that has no dedicated servers. All computers are equal
pharming when a phisher changes DNS server information so that the victim is directed to another site.
phishing trying to get someone to give you their personal details
plain text an un-encrypted message
pointer a variable that contains an address. The pointer points to a memory location of that address
polymorthism two or more objects can respond to the same message in different ways
Post-order tree traversal "Left
power of turing machines no phyical computer can be more powerful than a turing machine
precision the maximum number of significant digits that can be represented
pre-order tree traversal "Node
primary key an attribute which uniquely identifies an entity
Principle of univerality a universal machine is a machine capable of simulating any other machine
priority queue each element of the queue has an associated priority
pseudo-random numbers a series of numbers generated by software with apparent randomness.
queue a first in first out data structure
real number a number with a fractional part
real time operating system inputs are proccesed in a timely manner under time constraints
realtive error the absolute error divided by the actual number
Recursion Deffining a program in terms of it's self
referential integritty if a value apears as a foreign key it must be a primary key in another.
Regular expression a notation for defining all valid strings
Regular Language Any language that a FSM will acsept
relationship an association between 2 entitys
remote login connecting to a computer via the internet
rounding error the precision of an arithmetic function is greater than the representable value.
SaaS "software as a service
space complexity how much memory an olgorithm needs
sandbox a tightly controled set of resources for guest programs to run in.
scientific notation "a real number represented by a sign
serial data transmission signle bits are sent one after another along a single wire
server operating system an operating system designed to provide one or more specialised services
spam unsolicited junk emails
stack a last in first out data structure
stack frame the locations in the stack used to store the values reffering to one invocation of a routine
stand-alone computer a computer that is not networked and requires all of its own devices
state history consists of state descriptiond at each of the chronological stages of instances
State Transition diagrams a directed graph whose nodes represent the states and edges represent transitions.
system program a program that mannages the operation of the computer
time complexity how much time an algorithm takes to run
thin-client network a network where all processing is done by a central server.
topology "the shape
tractable a problem that has a reasonable time solution
tree "a connected
Trojan a program that hides in desirable programs.
travelers problem a problem of visiting each city and then returning to a starting point (intractable)
Turing Machine an FSM that controls one or more tapes of infinate length
underflow the value is to small to be represented using the number of bits availible
virtual machine the apparent machine that the operating system presents to the user to hide the complexities of hardware
Virus a small program attached to another program or data file.
web 2.0 software that becomes a service offered over the internet.
web server extension a program running on a web server that extends the functionality and allows content in real time.
web services self contained modular applications that are located on the web
wide area network a set of links that connect a large geographical area.
Wi-Fi IEEE 802.11 that supports wireless networking of home and buissness networks
worm a small program that exploites a network or security weekness
1st Normal Form No repeating attributes
2nd Normal Form No non-Key dependancies
3rd Normal Form No partial dependancies
Created by: henryh