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AQA Computing A2
Deffinitions
| Term | Definition |
|---|---|
| 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
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