Key Definitions Flashcards
(141 cards)
1
Q
Flat File
A
A set of single tables with no links between them.
2
Q
(Relational)
database
A
A set of related tables with links between them
3
Q
Primary key
A
A field or combination of fields that uniquely identify a record in a table
4
Q
Foreign key
A
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.
5
Q
Indexes
database
A
Indexes are separate data structures that are set up to improve access time to records
6
Q
First normal form
A
This is a database where tables contain no repeating attributes or repeating groups of attributes.
7
Q
Second normal
form
A
This is a database where tables contain no repeating
attributes or repeating groups of attributes and no partial dependencies.
8
Q
Third normal form
A
This is a database where tables contain no repeating
attributes or repeating groups of attributes, no partial dependencies and no transitive dependencies.
9
Q
Redundant Data
A
Data that is stored repeatedly
10
Q
Inconsistent Data
A
Multiple copies of data which are supposed to be the same but are in fact different
11
Q
Algorithm
A
A finite set of instructions designed to solve a specific task
12
Q
Procedure
A
A set of program instructions which perform a specific
task and can be called by another program.
13
Q
Parameter
A
A variable that can be passed to or from a procedure
14
Q
Passing by
reference
A
The address of the variable is passed to the
procedure.
15
Q
Passing by Value
A
A local copy of the variable is created for the procedure and discarded afterwards.
16
Q
Recursive
Algorithm
A
An algorithm that calls itself and has a base case to allow it to terminate.
17
Q
Database
Management
System
A
A piece of software which controls access to the data in a database, acting as an interface between the data and the application programs.
18
Q
Data inconsistency
A
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
19
Q
Data Redundancy
A
When the same data is stored more than once.
20
Q
Program-data
dependence
A
When the structure of the data within a program is defined as part of the program
21
Q
Program-data
independence
A
When data is separate from the programs that use that data
22
Q
Data Dictionary
A
Holds data about the database
23
Q
Database
administrator
A
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.
24
Q
Record Locking
A
A process to prevent access by others to a record while it is being updated
25
Data Warehouse
A large collection of data collected together from a variety of locations for efficient analysis.
26
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
27
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
28
Data Structure
A group of related data items which can be managed as a single set.
29
Queue
A first-in first-out data structure where items are added at the end and removed from the front.
30
Stack
A last-in first-out data structure where items are added and removed from the same end
31
Linked List
A set of data elements, where each element contains
the data itself
a pointer to the next element
32
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.
33
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.
34
Text-based
| interface
Input to the computer is typed usually by via a
| command prompt
35
Graphical User
| Interface
An interface where most communication is via screen elements such as windows, icons, menus, pointers etc
36
Forms Dialogue
Computer prompts for input into specific fields on a screen dialogue form
37
Speech
| recognition
Command and/or text input are given by human speech
38
Sound synthesis
The production of sounds resembling human speech by electronic methods
39
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
40
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
41
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.
42
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.
43
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.
44
Hexadecimal
| Representation
Group the bits into groups of 4 (from the right) and convert each group to hexadecimal representation
45
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.
46
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.
```
47
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
48
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
49
Overflow
Occurs when the result of a computation is too large to be represented in the system
50
Underflow
Occurs when an answer is too close to zero to be represented satisfactorily by the computer
51
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
52
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
53
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
54
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)
55
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.
56
NOT
Gives 1 if 0 and 0 if 1.
57
AND
Gives 1 if both are 1’s and 0 otherwise
58
OR
Gives 1 if one or both are 1s, 0 only if both are 0s
59
XOR
Gives 1 if only one of the bits is a 1, if both or neither are 1s then gives 0.
60
Masking
Uses AND. Turns off bits when 0 is used and lets them through unchanged if 1 is used
61
Half duplex
Where data transmission is two-way, but only one direction at a time
62
Multiplexing
Where data from several independent sources are combined to be sent along a single route to a single destination.
63
Parallel data
| transmission
Where the bits for a character are sent
| simultaneously along separate data transmission lines
64
Duplex
Two-way data transmission, and data can be both transmitted and received at the same time
65
Serial data
| transmission
Where the bits for a character are sent one after another along the same data transmission line from source to destination
66
Simplex
Where data transmission is one-way only.
67
Switching
Switching is a method of data transmission where a message is sent only to its intended recipient rather than being broadcast to all the stations on the network
68
Sequential File
A file where records are stored in key field order
69
Index
Contains the key field and the record address on disc
70
Indexed
| Sequential File
A file where records are stored in key field order and an index is used to allow records to be accessed directly.
71
Three-level index
There is a main index which contains the location of the next index. This in turn will contain the location of a second index, which contains the location of the last index containing the physical address of the record.
72
Multi-level index
In a multi- level index , the above process continues for the appropriate number of levels of index before you reach the last index which contains the physical address of the record
73
Random Access
| file
Random access files use a hashing algorithm and an overflow area
74
Hashing Algorithm
A hashing algorithm takes the key field as an input to an algorithm which calculates the disc address. The address generated is called the home block
75
Overflow area
If there is no room in the home block the record is placed in the overflow area and a pointer is left in the home block to indicate that an overflow has occurred.
76
Biometric
A biometric is a unique physical characteristic of an individual that can be checked automatically by a computer.
77
Encryption
Encryption means converting data from plain text into secret code. Data encryption/decryption involves using an algorithm and key (i.e. numeric code). To
decrypt the data an authorised user needs the key and then applies the same algorithm to reverse the encryption.
78
Generations of
| files
Every time a master file is updated, the original file is copied together with any changes (held on the transaction file) to a new master file. A generation file backup system involves storage of the most recent
master files with the transaction files so that if the current version of the master file becomes corrupted it can be restored
79
Transaction Log
Transactions logs are used in real-time transaction processing systems. They keep a record of all the transactions that have taken place since the backup was made (usually the previous night). If the file becomes corrupted the previous backup is used and
the transactions stored in the transaction log are applied to automatically update the file to the state immediately before failure. That way no transactions are lost
80
Record Locking
In any real-time transaction processing system, if a record is accessed for update it is locked so that two users cannot update it at the same time. This prevents errors such as double bookings or the same item of stock being sold twice
81
Archive File
An archive file contains data no longer in use but is stored securely for historical purposes. For example for tax purposes, legal reasons or for the auditors
82
Batch system
A system where the process continues from
| beginning to end without user Interaction
83
```
Single user (standalone)
system
```
A system where the computer is not connected to others by a network and cannot share other devices
84
Multi-programming
| system
A system which allows more than one program to be held in memory at the same time and apparently processed simultaneous. This requires the memory to
be partitioned and the different tasks to be scheduled to allow them to run
85
Multi-user (multiaccess)
| system
A system which allows several users to work on the same computer at the same time
86
Multi-tasking
| system
This allows several different tasks or applications to be available to a user at the same time.
87
Partitioning
The operating system splits the memory into chunks and allocates each process a chunk to reside in. The partitions are usually variable so each process can be
given a suitable amount of RAM. When the process is finished the chunk of memory is released
88
Paging
Conveniently manageable fixed-sized blocks of memory. Programs are split into virtual pages and they are pages in and out (swapped between physical memory (in RAM) or virtual memory (on disc – if not being currently used) as required by the operating system
89
Buffering
An area in main memory used to temporarily hold the data as it is transferred between the CPU and a slower peripheral to compensate for the difference in operating speeds.
90
Double buffering
Double buffering is an advanced form of buffering in which two buffers are used, so that one may be filled while the other is being emptied. This speeds up the process. It is suitable for e.g. a printer queue where
there tends to be lots of data transferred. A single buffer is adequate for a keyboard.
91
Interface
The hardware and associated software needed for communication between processors and peripheral devices which compensates for the differences in operating speed, voltages etc.
92
Time-slice
A time-slice is a finite maximum amount of processor time that a process is allowed to run for in a multiprogramming
system
93
Ready task
A ready task is one waiting for processor time. (not running because another task is currently being run)
94
Running task
A running task is one that is currently being executed by the CPU
95
Blocked Task
A blocked task is one that is waiting for an event e.g Input or output operation
96
Polling
Polling is the when each process is asked whether it requires a time-slice
97
Interrupt
An interrupt is a signal generated by a device or software requesting attention
98
Scheduling
This is the process of deciding which job is to be processed next (may be prioritised) (done by the scheduler)
99
Link Editor
The software tool that allows already compiled object code files or modules to be combined with the completed program and then converted directly into an executable file.
100
Loader
Copies compiled object code from backing store into main memory ready to be run
101
Link Loader
The software tool which combines already compiled modules/subprograms into the executable program (at run time)
102
Editor
A program that allows the input and amendment of programming source code
103
Translation
| program
A program that translates a program into machine code
104
Compiler
Program that translates an entire high-level language source program into machine code all at once to form an independent executable file
105
Interpreter
Program that translates a high-level language into machine code one instruction at a time. Each instruction is executed before moving onto the next one
106
Assembler
A program that translates assembly language programs into machine code.
107
Debugger
Programs that provide a large range of facilities enabling the programmer to investigate conditions when errors occur
108
Program design
| language checkers
Software that checks for obvious errors in program designs written in PDL (special language used to design programs)
109
Application
| generators
An application generator is a software tool which is used to assist and speed-up the creation of a system.
It provides a complete environment to support the programmer often as part of an integrated development environment and usually creates code automatically. It may also include an interface generator and debugging tools.
110
CASE Tools
Software application that provides a number of functions which can assist with software development
111
Standard Modules
Modules perform standard or commonly used tasks which are used by more than one program such as Input validation, sort routines
112
Relocatable Code
Code in which the instructions may occupy different memory locations as determined by the operating system every time they are loaded
113
Subprogram
| Library
A collection of well-tested precompiled routines to perform common tasks that a programmer can use to speed up development time as no need to write them
again and less likely to contain errors.
114
Parallel processing
The simultaneous use of several processors to perform a single job. Job split up into tasks which can be performed by any available processor
115
Translation Error
These are errors detected during compilation and are usually syntax errors for example not having the correct number of brackets
116
Linking Errors
Linking errors happen when the compiled program is linked to a library routine, for example, if the wrong number of parameters has been passed or the routine is not present in the library
117
Execution Errors
These are errors detected during the actual running of the program. They can be caused by mistakes in the processing algorithm or the effects of unusual data not being catered for in the program. Examples are overflow errors or division by zero errors.
118
Program Trace
| Facilities
These are a position within the program where the program is halted as an aid to debugging
119
Program Break
| Point
This allows the programmer to step through the program one statement at a time and see the path taken through the program.
120
Store Dump
This is the output of an area of memory to a file or the screen usually showing the information in binary or hexadecimal numbers. It can be printed or listed to
the screen
121
Variable Watch
These display or list the value of the chosen
variable(s) while the program is running. It can be used while the program is being traced to investigate the changing value of key variables so they can be compared to their expected values.
122
Error Diagnostics
These are messages provided by the application diagnostic programs which attempt to detect, locate and log errors and additional information needed to solve the problem which can be investigated, acted
on or passed onto technical support services if necessary.
123
Backus Naur Form
This unambiguously defines the syntax of a computer programming language.
124
Procedural
| language
One in which the programmer specifies the steps required to perform the task using programming statements, declarations and control structures. They also allow programming statements can be grouped
together into smaller self-contained units called procedures or subroutines
125
Declarative or Non
Procedural
Languages
These are non-procedural languages, i.e. the
programmer states what has to be done but not how to do it. The program is made up of a set of facts and rules, the order of which is not important. E.g. Prolog
126
Object oriented
programming
Languages
An approach where both data, and the code for the operations that are applied to the data, are combined into programming structures called objects
127
Object
A collection of data fields (properties or attributes), together with the procedures and functions (methods) that operate on those fields
128
Class
A set of objects that share a common data structure and common behaviour.
129
Encapsulation
The fact that objects are self-contained and therefore they are easy to import into another program.
130
Inheritance
We can create sub-classes of a class with subclass (derived class) inheriting all the properties and methods from a parent class (base class). Additional properties and methods can then be added to the subclass. This can really speed up development time
131
Special Purpose
| Languages
Sometimes languages are developed to solve a particular problem or provide the functionality for a specific situation or need.
132
VLE
A virtual learning environment (VLE) is a software system designed to help teachers in the management and use of learning material.
133
Ecommerce
Ecommerce is the use of computer technology (particularly the Internet) for commercial operations like sales from businesses to customers or from business to other businesses
134
Web log
A web log is a set of entries or diary on the world wide web / internet which is accessible to other web users
135
Instant Messaging
IM is an application that allows people to
| communicate in real time on the Internet using text based messages
136
Search engine
A Search engine is a tool accessed over the Internet, which can be used to search for web sites on a particular topic
137
Internet
Internet is a world-wide networked information and communication system freely available via any connected computer/device
138
Extranet
If a company allows some access from outside its
intranet, it becomes an extranet. Access would normally be through a firewall to allow only the permitted users to access the data
139
Protocol
A set of rules used to ensure the proper transfer of data between devices specifying, for example the data formats and the signals that start, control and end the transfer.
140
Router
A device in a network which holds information about the addresses of computers in the network or other
networks and can send data to the correct destination computer or network.
141
Data Collision
When two sets of data are detected on the network simultaneously
