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IGCSE I.C.T. Theory

ict
by

juanjo mariño

on 2 April 2014

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Transcript of IGCSE I.C.T. Theory

Advantages
What are barcodes?
Barcodes
Disadvantages
How to read barcodes
A barcode is an optical machine-readable representation of data relating to the object to which it is attached. Originally barcodes represented data by varying the widths and spacings of parallel lines. Later they evolved into rectangles, dots, hexagons and other geometric patterns in two dimensions (2D). Although 2D systems use a variety of symbols. Barcodes originally were scanned by special optical scanners called barcode readers; later, scanners, desktop printers and smartphones.
Want to know more?
Try scrolling in letter "b"
Barcodes eliminate the possibility of human error.
A barcode scan is fast and reliable
It takes less time than entering data by hand.
They are very cheap.
They can be customized depending on
their purpose
If you want to know the advantages of barcodes you will need to scroll in lette "n"
Damaged Labels
Bar code readers cannot read labels that are wrinkled, dirty or smudged.

Training
The need to train employees, which can be a significant issue if the business is large.
Printer Requirements
Dot matrix and ink jet printers cannot print high-quality bar codes.
Scroll in letter "n" to know the disadvantages of barcodes
Barcode Readers
The earliest and cheapest barcode scanners are built from a fixed light and a single photosensor that is manually "scrubbed" across the barcode.
Like the keyboard interface scanner, USB scanners are easy to install and do not need custom code for transferring input data to the application program. On PCs running windows the HID interface emulates the data merging action of a hardware "keyboard wedge", and the scanner automatically behaves like an additional keyboard.
Barcode scanners can be used in Google's mobile Android operating system via both their own Google Goggles application or 3rd party barcode scanners like Scan. Nokia's Symbian operating system features a barcode scanner. With BlackBerry devices, the App World application can natively scan barcodes and load any recognized Web URLs on the device's Web browser. Windows Phone 7.5 is able to scan barcodes through the Bing search app.
Scroll in letter "d" to know more
Note that bar codes are made up of both white and black lines. The white spaces in between the black lines are part of the code.
Understand that there are four different thicknesses to the lines. Henceforth, the skinniest line will be referred to as "1," the medium-sized line as "2," the next largest line as "3." and the thickest is "4."

Recognize that each UPC bar code begins and ends with 101 (thin black, thin white, thin black). In the very middle of the bar code, you will notice two thin black lines sticking down between the numbers. The thin white between them, as well as the thin whites to either side, make up a 01010. Each UPC bar code has 01010 in the middle.
Recognize that each digit, including the small numbers that begin and end the bar code, has its own unique four-line set. 0 = 3211, 1 = 2221, 2 = 2122, 3 = 1411, 4 = 1132, 5 = 1231, 6 = 1114, 7 = 1312, 8 = 1213, 9 = 3112. Notice that the line colors are reversed after the center-line: The lines of the digits to the left are white/black/white/black whilst to the right they are black/white/black/white. This provides some error checking and allows the reader to know the direction in which it is scanning a code. It is also crucial so that the bar code ends with a bar rather than a space. So, actually, each digit has two codes.
So, the bar code above whose first two digits are 03 would start out "10132111411". Broken down this is "101-3211-1411" where 101 marks the beginning of the bar code and 3211 marks the digit 0 .
Networks
Most computer systems are connected together to a form which is known as a network.
Scroll in letter "o" to know more
Local Area Networks
A local area network (LAN) is within one building, not over a large geographical area. It consists on a number of computers and devices. One of the hubs will be connected to a router and modem to allow the LAN to connect to the internet, By doing this it becomes a Wide are network (WAN)

ADVANTAGES
Sharing of resources
Communication between users
There is a network adminstrator

DISADVANTAGES
Easier spread of viruses
Printer queues
Slower acces to external networks
Scroll in letter "c" to know more
Ring Networks
Scroll in letter "e"
Every computer is connected to a ring, including server. Data is transmitted along the ring.

ADVANTAGES
Work well under heavy loading
Possible to create large networks

DISADVANTAGES
If there is a fault in the wiring between two computers, the whole network will fail.
Adding a new device or computer can be difficult
Bus Networks
Each computer is connected to a common central line. Data travels along this line until it reaches the required device.

ADVANTAGES
Easy to add a new computer
Does not affect the network if one computer fails

DISADVANTAGES
Difficult to isolate any fault
The network fails if the central wire fails
Star networks
Each computer is connected via a central hub or switch.

ADVANTAGES
If one computer fails, it does not affect the rest of the network
Problems on the network are easy to identify
Easy to expans the network

DISADVANTAGES
If the central hub breaks down the whole network crashes
Tree Networks
It has a central line that connects a series of star networks.The server is also connected to the central line.

ADVANTAGES
Network is not affected if one computer fails.
Problems in the network easy to spot
Network easy to expand

DISADVANTAGES
If the central line breaks down, the whole network cashes
Wireless LANs
Similar to LANs but there are no wires. Access points are connected into the wired networks at fixed locations.Limited use because it has a small range of 30 to 50 metres.
Scroll in letter "A"
Scroll in letter "e"
Want to know more?
Try scrolling in letter "e"
IF you want to know about tree networks scroll in letter "e"
Chapter 8
Chapter 7
IGCSE Theory I.C.T.
Chapter 1
Chapter 4
Chapter 6
Chapter 2
Chapter 3
Chapter 5
Systems analysis and design
Observation
Questionnaires
Interviews
Looking at existing paperwork
Description
Advantages
Disadvantages
Involves watching personnel using the existing system to find out exactly how it works.
The analyst obtains reliable data
It is possible to see exactly what is being done
It is relatively inexpensive method
People are generally uncomfortable being watched and may work in a different way
If workers perform tasks that violate standard procedures, they may not do this while being watched!
Description
Advantages
Disadvantages
Involves sending out questionnaires to the work force and to customers to find out their views of the system and to find out how key tasks are carried out
The questions are answered quickly
Inexpensive method
Individuals can remain anonymous
Allows quick analysis of the data
Often, number of questionnaires returned is low
Questions are inflexible, since they have to be generic
There is no way to clarify a vague or incomplete answer to a question
Description
Advantages
Disadvantages
Allows the analyst to see how paper files are kept, look at operating instructions and training manuals and check the accounts.
Allows information to be obtained which was not possible by any of other methods
Analyst can see for themselves how paper system operates
Allows analyst to get some idea of the scale of the problem, memory size requirements, type of input/output devices needed
Can be very time consuming
Expensive method due to the analyst's time
Advantages
Disadvantages
Description
Involves a one-to-one question-and-answer session between the analyst and employee/customer.
Gives opportunity to motivate the interviewee into giving open and honest answers to analyst
Allows analyst to probe for more feedback from the interviewee, also easier to extend a question
Possible to modify questions as interview proceeds and also ask specific questions
Good method if analyst wants to probe deeply into one specific aspect of the system
Can be time consuming
Expensive, due to use of analyst time
interviewee cannot remain anonymous
TYPES OF COMPUTERS
A large, very powerful computer system.

Uses
To run commercial applications such as banking and insurance, where huge amounts of data are processed every day.

Advantages
Can have several CPUs.
Very fast processor speeds.
Can support very fast processor speeds and multiple operating systems
Huge amounts of storage capacity.
Can do large jobs which require a large memory and fast processor time.

Disadvantages
Have to be permanently housed in a large room, and can not be moved around.
Very expensive to operate and maintain
Mainframe computers
A computer that can almost fit into a hand and is a smaller version of a laptop.

Advantages
Low weight.
Low power consumption.
A processor that does not generate too much heat.
Easy to transport.

Disadvantages
No optical drives.
Very small keyboard.
Limited battery life.
Netbooks
A type of computer where the monitor, keyboard, pointing device and processor are all together in one single unit.

Advantages
Very portable, since all components are all together in one single box.
No trailing wires.
Can take full advantage of “Wi-Fi”.
Can link into any multimedia system.

Disadvantages
Easy to steal.
Limited battery life.
Some components might be too small to use comfortably.
Heat dissipation is more difficult.
Laptop computers
It is made up of separate monitor, keyboard, mouse and processor unit. “Personal Computer” usually refers to computer systems which are IBM-compatible.

Advantages
Spare parts and connections tend to be standardised, and have a low cost.
Desktops usually have a better specification for a given price.
The large casing allows good dissipation of any heat build-up.

Disadvantages
Not portable because it is made up of separate components.
All components need to be hooked up by wiring.
Because it is not portable, you need to copy files when you want to do some work elsewhere.
PC/Desktop computers
Small hand held computers that usually come with a touch screen that is usually activated using a stylus. Data is entered by using a keyboard that appears on the touch screen.

Advantages
Can be used anywhere because of their size.
Very lightweight and are very portable.

Disadvantages
Difficult to enter text quickly.
Very limited capabilities due to the software and the operating sistem used.
Personal digital assistants
Input devices
Input devices
Webcams
Uses
Used to enable conferencing to take place
Advantages
Can be left on constantly
Allow people to keep in contact with each other without the need to travel
Disadvantages
Very limited features, picture is often of poor quality
They need to be connected to the computer
Input devices
Light pens
Uses
Used for selecting objects on CRT screens
Used for drawing on screen
Advantages
More accurate than touch screens
They are small and easy to use
Disadvantages
Only work on CRT monitors
Not very accurate when drawing
Input devices
Graphics tablets
Uses
Used to produce drawings and computer graphics
Used in computer aided design (CAD) work
Advantages
Very accurate method of drawing
Disadvantages
More expensive than other pointing devices
Input devices
Sensors
Uses
Different types of sensors: temperature, pressure, light, sound, humidity/moisture and pH
Advantages
Readings are continuous
Readings are more accurate than those taken by human operators
Disadvantages
Faultyu sensors can give spurious results
Input devices
Microphones
Uses
Used to input speech/sounds
Used in voice recognition software
Advantages
Faster to read in text than type it in using a keyboard
Disadvantages
Sound files use up a lot of memory
Not as accurate as typing in manually
Input devices
Digital cameras
Uses
Used to produce photographs
Used to produce short video clips
Advantages
Easy to delete an image from memory
The memory card can store hundreds of photographs
Disadvantages
Resolution not as good as traditional cameras
Input devices
MICR readers
Uses
Used to process cheques in banking operations
Advantages
Greater security than OCR
Disadvantages
Only certain characters can be read
Quite expensive
Input devices
OCR readers
Uses
Used to process passports and identity cards
Advantages
Errors reduced since there is no manual entry
Much faster data entry than system than manually keying in data
Disadvantages
Not very accurate
Has difficulty reading handwriting
Input devices
OMR devices
Uses
Used to read questionnaires and multiple-chioce examination papers
Advantages
Very fast way of inputting the results of a survey
Disadvantages
The forms need to be carefullyt designed to make sure the marks are correctly positioned
Input devices
Barcode readers
Uses
Used in supermarkets and shops where goods are marked with a barcode
Advantages
Faster than keying in data manually
Fewer mistakes are made
Barcodes enable automatic stock control
Disadvantages
The system isnot foolproof
Input devices
Scanners
Uses
Used to scan in documents
Old valuable documents can be scanned
Advantages
Much faster and more accurate than typing again a document
It is possible to recover damaged documents
Disadvantages
Quality can be limited, depending on the scanner resolution
Input devices
Chip and PIN readers
Uses
Used where payments are made using cards
Advantages
More secure payment system than a magnetic stripe or requiring signature
More robust system than a magnetic stripe readers
Disadvantages
Need to be careful that no one reads your PIN
Input devices
Smart card readers
Uses
Used in ID cards, electronic passports and driving licenses
Advantages
Reduce need to carry cash
Disadvantages
If lost, information could be used in identity theft
Input devices
Magnetic stripe readers
Uses
Used for travel systems, security cards, credit and debit cards
Advantages
Data entry is faster than a keyboard
No errors
Prevent acces to restricted areas
Disadvantages
If damaged, data is lost
Input devices
Touch screens
Uses
Used in PDAs and mobile phones
Used for self-service tills
Advantages
Options are easy to choose
Disadvantages
Limited options available
Gets dirty frequently
Input devices
Joysicks
Uses
Used in video/computer games
Used in simulators
Advantages
Control is in three dimensions
Disadvantages
More difficult to control the pointer than with a mouse
Input devices
Remote controls
Uses
To remotely control devices
Advantages
Can use them from any distance
Disadvantages
The signal can be easily blocked
People with limited hand movement find them difficult to use
Input devices
Trackerballs
Uses
Opening, closing and minimising software
Grouping, moving and deleting files
Advantages
People with limited hand movement find it easier to use than a mouse
Disadvantages
Not supplied with the computer
Input devices
Touchpads
Uses
Opening, closing and minimising software
Grouping, moving and deleting files
Advantages
Rapid navigation through applications
Can be sed without a flat area
Disadvantages
Difficult to “drag and drop” with them
More difficult to control the pointer than with a mouse
Input devices
Mice
Uses
Opening, closing and minimising software
Grouping, moving and deleting files
Advantages
Rapid navigation through applications
Disadvantages
Difficult to use without flat area
Input devices
Numeric keypads
Uses
To only enter numbers
Advantages
Easy to carry around
Faster to enter data than standard keyboards
Disadvantages
Difficult to enter text with them
Difficult to use due to small keys
Input devices
Keyboards
Uses
Input data into applications softwarre
Advantages
Fast entry of text into a document
Easy use
Disadvantages
Users with limited arm use find them difficult to use.
1. Analysis
2. Design stage
Design Input Forms
Design output forms and Reports
Produce Flowcharts
Produce Pseudo Codes
Selecting and designing Hardware/Software requirements
3. Development and Testing
4. Implementation
Direct Changeover
Parallel Running
Pilot Implementation
Phased Implementation
Output Devices
Output devices
Multimedia projectors
Uses
Used for training presentations
Used for advertiising presentations
Advantages
Enable many people to see a presentation
Disadvantages
Images can be fuzzy
Expensive to buy
Setting it can be difficult
Output devices
Plotters
Uses
Used to produce large drawings
Can print on plastic-coated paper
Advantages
Can produce large printouts
Print quality is extremely high
Disadvantages
Slow in operation
Expensive to buy and maintain
Output devices
Dot matrix printers
Uses
Can be used in noisy enviroments where print quality is not very important
Advantages
Carbon copies or multi-part outputs can be produced
Cheap to run and maintain
Disadvantages
They are very noisy
Output devices
Inkjet printers
Uses
Used where low output volumes are required
Advantages
Output is of high quality
Cheaper to buy than laser printers
Very lightweight
Disadvantages
Output is slow
Ink cartridges run out too quickly
Output devices
Laser printers
Uses
Best option for fast high quality high volume printing
Advantages
Printing is fast for high volumes
Can handle very large print jobs
Disadvantages
Expensive to buy
Produce ozone and volatile organic compounds
Output devices
Speakers
Uses
Used to output sound from multimedia presentations
Used in home entertainment centers
Can help blind people through audio outputof text on the screen
Used to play downloaded sound files
Output devices
TFT monitors
Uses
Used in computers to make the user see what they are typing in
They are an integral part of laptop computers
Advantages
Lightweight
Consume less power than CRT monitors
Disadvantages
Definition not as good as CRT monitors
They cannot be used with light pens
Output devices
CRT monitors
Uses
Used in computers to make the user see what they are typing in
Used with light pens
Advantages
Produce a higher quality image than TFT monitors
Disadvantages
Tend to be heavy
Consume more power than modern TFT monitors
Output devices
3D inkjet printers
Uses
Used to produce prototypes
Advantages
3D inkjet printers save a lot of money
Disadvantages
Expensive to buy
Slow at producing thir output
Control devices
Control devices
Actuators
Actuators are transducers
They are used to take signals from a computer and convert them into some form of motion
Control devices
Heaters
Actuators are connected to switches which turn the heater on or off
Uses
Used in automatic washing machines, cookers and central heating systems
Used in automatic greenhouses to control the temperature
Control devices
Lights
The actuator is connected to the switch that turns the lights on or off
Uses
Used for security lights
Used in greenhouses to control the lighting conditions
Control devices
Buzzers
The buzzers are switched on or off by the actuator
Uses
Used in cookers and microwave ovens to tell the operator when the cooking process is complete
Used in burglar alarm systems to warn if intruders are present
Control devices
Motors
The motor is turned on or off by the actuator
Uses
Used in many domestic appliances
In industry, they are used to control robot arms
In computers, they operate fans, disk drives and DVD drives
Storage Devices and Media
Storage devices
Flash memory cards
Uses
Used to store photos on digital cameras
Used on mobile phones as memory cards
Advantages
Very compact
Very robust
Disadvantages
Relatively expensive
Lower storage capacity than hard disks
Storage devices
Memory sticks/pen drives
Uses
Used for transporting files between computers or as back-up store
Used as a security device
Advantages
Very compact and portable media
Very robust
Disadvantages
Easy to lose due to their small size
Storage devices
DVD-RAM
Uses
Used in camcorders to store films
Advantages
Have a long life
Possible to re-write over 100,000 times
Disadvantages
Many sistems will not recognise their format
Relatively expensive
Storage devices
CD-R and DVD-R
Uses
Used for home recordings of music and films
Advantages
Cheaper than RW disks
Once burned they are like ROM disks
Disadvantages
Can only be recorded once
Storage devices
CD-ROM and DVD-ROM
Uses
CD-ROMs used by manufacturers to store music files and software
DVD-ROMs have larger capacity and are used to store films
Advantages
Hold more data than floppy discs
Disadvantages
Data transfer rate slower than hard disks
Storage devices
Floppy disk drives
Uses
Used where small files need to be transferred
Advantages
Very simple technology
Low cost item
Disadvantages
Low memory cappacity
Not robust
Storage devices
Fixed hard disk
Uses
Used to store the operating system and working data
Used for storing applications software
Advantages
Have a very fast data transfer rate
Fast access times to data
Large memory capacities
Disadvantages
Can be easily damaged
Storage devices
Blu-ray disks
Uses
Used in home video consoles
Used for storing and playing back films
Advantages
Large storage capacity
Fast data transfer rate
Disadvantages
Relatively expensive
Storage devices
CD-RW and DVD-RW
Uses
Used to record radio and television programmes
Advantages
Can be re-used many times
Not as wasteful as the R format
Disadvantages
Expensive media
Possible to accidentaly overwrite data
Storage devices
Magnetic tapes
Uses
Used as back-up data media
Used in applications where batch processing is used
Advantages
Very robust technology
Data transfer rate is fast
Disadvantages
Access time is slow
Storage devices
Portable hard disk drives
Uses
Used as back-up systems to prevent loss of data
Used to transfer data, files and software
Advantages
Data transfer is fast
Large memory capacities
Disadvantages
Can be easily damaged
5. Documentation
User:
How to:
Log in
Load Files
Search
Print

Hardware/ Software
Error handling
Trouble Shooting
Tutorials
Technical:
Purpose of System
Coding
Programming Language
Flowchart/ Algorithm
Hardware/Software requirements
Known bugs
Validation Rules
6. Evaluation
Identify Limitations
Necessary Improvements
Compare test results: 1. From new system
2. With old system
Interviews
Questionnaires
Results may require Software/ Hardware update
Verification and Validation
Verification
A way of preventing errors when data is copied from one medium to another.
Two common ways:
Double entry: data is entered twice, using two different people.Computer compares the two entries and identifies any differences
Visual check: checking for errors by comparing entered data on the screen with data in original document
Validation
Process where data is checked to see if it satisfies certain criteria when input into a computer.

Different validation techniques:
Range check
Length check
Character/type check
Format/picture check
Limit check
Presence check
Consistency check
Check digit
Old system is stopped overnight and new system introduced immediately.

Advantages:
Benefits are immediate
Costs are reduced, since only one system is used
Less likelihood of a malfunction since new system will have been fully tested

Disadvantages:
Method can be disastrous if new system fails
Old and new systems are run side by side for a time before new system takes over altogether

Advantages:
If new system fails, old system is still available as a back-up
Possible to train staff gradually
Staff have time to get used to new system

Disadvantages:
More expensive than direct changeover, extra staff needed to run both systems altogether
New system introduced into one part of the company and its performance assessed

Advantages:
If new system fails, only one part of the company affected
Possible to train staff in one area only, much faster and less costly than parallel running
Costs less than parallel running, only one part of system is being used in the pilot

Disadvantages:
More expensive than direct changeover, each pilot scheme needs to be evaluated before next stage is introduced
Expert Systems
Knowledge Base
Database designed to allow complex storage and retrieval requirements of a computerised knoledge-based manage system (in support of expert system)
Inference Engine
Software that attempts to derive answers from the knowledge base using a form of reasoning. It is how expert systems appear to use human-like reasoning when accessing information from the knowledge base in an effort to find a conclusion to a given problem. It is a type of reasoning engine.
Rules Base
Made up of a series of 'interference rules'. These influence rules used by the inference engine to draw conclusions. Closely follow human-like reasoning
Advantages
Expert systems provide consistent answers
Never 'forget' to answer a question when determining the logic
Reduced time taken to solve a problem
Less skilled work force is needed, saves money, allows areas of the world access to expertise which they could not normally afford
Disadvantages
Tend to lack common sense in some of the decision-making processes
Errors in knowledge base can lead to incorrect decisions being made
Can be expensive to set up
Considerable training necessary to ensure the system is used correctly by operators
New system is introduced into one part of company and performance assessed

Advantages:
If new system fails, only one part of company affected
Possible to train staff in one area only, faster and less costly than parallel running
Costs less than parallel running, since one part of system being used in the pilot

Disadvantages:
More expensive than direct changeover, each pilot scheme needs to be evaluated before next stage is introduced
Initially, only part of new system introduced. When it proves to work, next part introduced until old system fully replaced

Advantages:
If latest part fails, only necessary to go back in the system to point of failure.
Possible to ensure system works before expanding

Disadvantages:
More expensive than direct changeover, necessary to evaluate each phase
Communication Systems
Multimedia presentations
Presentations using animation, video and sound are more interesting than one done on paper. Presented with a multimedia projector so that the audience is able to see it.

Advantages:
Use of sound and animation/video effects
interactive/hyperlinks built into presentation
More likely to hold audience's attention

Disadvantages:
The need to have special equipment, expensive
Sometimes requirement for internet access.
Paper-based presentations
Presentations in a hardcopy format

Advanatages:
Disabled people do not have to go to the venue to see presentation
Possible to print out in Braille
Recipients have a permanent copy

Disadvantages:
Presentation needs to be distributed
No special effects
There are printing costs
Flyers and posters
Produced by word processors and desktop publishers. They usually have photos.
Websites
The ways ICT is used
Advantages:
Sound / Video / Animation
Hyperlinks …
Hot spots
Navigation
Hit counters

Disadvantages:
Can be hacked
Viruses
Modified
Computer with Internet
Lack of portability
Maintainance
Music production
Data Types
Digital data
Discrete, fixed values in a given range
Analogue data
Real world data
Continuously variable
Infinite number of values within a given range
Length, Weight, Temperature, Pressure
Analogue & digital data
Faster data retrieval
Easy expansion (Add a table)
Data integrity
All other data is up to date once an update is made as data is not repeated
A foreign key in one table is a primary key in another
Relational databases cont.

Introduced in 1970
A number of tables
Primary Key
Combine data from different tables to create a report
No need to repeat data
Relational databases
Structured to allow
Manipulation
Searches
Up to date info for external applications
Data duplication minimised
Easy to expand
Secure as controlled by front end
Reports generated

Databases
Data Types
Computers only understand digital
Must use an adc

If a computer is used to control an analogue device then a digital to analogue converter is required

Analogue to digital Converter (AdC)

How do we know the values…
Speedometer
Position of pointer on a dial

Thermometer
Height of liquid

Sensors measure these physical, analogue quantities
Analogue devices
Contains all the data in one table

Flat file structure
Unique
Used to locate a record in a file
Primary Key / Key field
DD/mm/yyyy
DD/mm/yy
DD.mm.yy
mm/DD/yyyy
yyyy/mm/DD
DD mmmm yyyy
DD-mmm-yyyy
Date Data
Integer
Whole numbers (+ive or –ive)

Real
Everything
Numeric
Text
A to Z
Alphanumeric
A to Z anD 0 to 9

Declankeogh………………Text
Declankeogh01……………Alphanumeric
Alphanumeric
Logical / Boolean

Alphanumeric / Text

Numeric

Date
Types
Data stored in files

Files consist of records

RecorDs contain fields
Data structures
True / False
Yes / No
1 / 0
binary 1/binary0

AND – True for both cases
OR – true for at least one case
Logical / Boolean
Once the system analyst knows what needs to be done and what the problems of the system are, he can start to
If the system contains files, the file structure (length of each field, key field) needs to be finalised. Once structure has been determined, it is created and tested. How the hardware is used to interface with the user needs to be identified.
Development stages
Testing Strategies
Testing of each module needs to be done to ensure each one functions correctly on its own. Once each module has been developed, the whole system needs to be tested.
Types of data:
Normal:
Data which is valid and has an expected outcome
Extreme:
The data at the limits of validity
Abnormal:
Data outside the limits of validity and should be rejected
Full transcript