It is a term used to describe the stages in an ICT project.
Commonly it is the process by which an existing system is replaced with another.
Definition of the problem
Feasibility study
Collection of information
Analysis
Design
Implementation
Evaluation
Installation
Maintenance
An illustration of the systems lifecycle...
Definitions: What is done at each Stage
Problem Definition
Define problem the system is to overcome
Feasibility Study
Looks at alternative solutions
Evaluation: Is the project worth doing:
T echnically Feasible: (i.e. Can it be done?)
E economically Feasible: (i.e. Is it worth doing?)
L egally Feasible: (i.e. Is it within the law?)
O perationally Feasible: (i.e. Can it be done)
S equentailly Feasible: (i.e. Can it be in time - e.g. Ticket system for The World Cup)
Information Collection
Define how old system works and problems
Analysis
Analyse how current system works
iThss uses lots of diagrams and flowcharts
Design
Exact details of requirements are defined
Implementation
Establishing new system in the organization
Evaluation
Does the finished solution meet its requirements?
Does it solve the problem?
Installation
How to install new system
Maintenance
Fix minor Problems;
Adapt system to cope with changes
tweaks to improve system (e.g Speed up slow processing);
Back up data;
Upgrade peripherals;
relocate system
Implementation Issues:
If a team of programmers have to be employed, problems can occur such as multiple uses of the same variable, but for different functions (an area like this is where bugs can)
Installation Approaches:
An analyst must decide how to install system into business,
o Big Bang Approach
Switch off the old system and switch on the new.
o Parralell Approach
You run the old and new system in parallel for a time.
o Phased Approach
You run only part of the new system .
Methods of Implementation
The waterfall model is one model of the cycle in w
hich progress is seen as flowing steadily downwards (like a waterfall) through the phases of: 1. Conception
2. Initiation
3. Analysis
4. Design (Validation)
5. Construction
6. Testing
7. Maintenance
The first formal description of waterfall model is often cited to be from an article published in 1970 by Winston Royce.
USE: Well suited to projects that have low risk in the areas of user interface and performance requirements, but high risk in budget and schedule predictability and control.
The spiral model is the most generic of the models.
Most lifecycle models can be derived as special cases of the spiral model.
Uses a risk management approach to software development.
Intended for large, expensive and complicated
Knowledge-based systems are software designed to be able to store vast amounts of data about a particular topic.
An expert system consists of 4 Parts
Set of Rules
Inference engine
HCI
Knowledge
This data can then be interrogated so that sensible information can be gleaned.
o Data is initially collected from specialist experts.
o The software is then used to replace the experts in conditions where the expert is unavailable.
Typical uses would be to provide medical diagnoses(NHS Direct) or to interpret geological data.
o Provide a platform on which applications can run
o Control hardware
o Allow communication with the outside world
SIX TYPES OF OPERATING SYSTEM
SINGLE USER – one user at a time.
MULTI USER – data centrally stored, e.g. supermarket checkout system.
MULTITASKING – allows multiple tasks to be run concurrently (or appear to).
BATCH – is an O/S where jobs run from begining to end without user intervention.
This originates from the 1950s, to stop people slowing down the few computers, similar tasks run sequentially.
DISTRIBUTED – centrally located data which is downloaded or process distributed to local machines be worked on.
REAL TIME – An O/S that produces an output immediatley so that the output can influenece the next input.
Used in safety critical systems; responses within a critical timeframe; failsafe conditions.
e.g. Flight Control, Nucleur power plant or Autopilot on plane.
Functions of an O/S
o Provide and manage hardware resources (memory management etc.)
o Provide Human Computer Interface between computer and user
o Provide interface between applications and the machine itself
o Provide security for the data on the machine
(particularly for multi users)
o Provide utility software for maintenance
With batch processing, jobs with similar needs are batched together.
They are run through the computer as a group.
Performance is increased by attempting to keep CPU busy at all times.
o Buffering, offline operation, spooling and multiprogramming.
Process of transferring data by placing it in a temporary folder where another program may access it for at a later
One of the purposes of the operating system is to provide a human-computer interface which lets users tell the computer what to do, and allows the computer to ask the user for input or to display results.
o GUI – Graphical User Interface
o WIMP – Windows Icons Menus Pointers
MENU BASED – often confused with GUI (menus). The whole interface is run from menus. Screens are in hierarchical layers so are often intuitive and simple.
FORM BASED – DVD film control. Multiple options displayed as forms where there are buttons to move forms.
GRAPHICAL USER
Great for beginners.
GUIs tend to be intuitive.
Context sensitive help.
Add-ons can cause actual software to be quite slow because of processing time.
Many commands are hidden so not to confuse the user.
COMMON INTERFACE
Many Windows applications use a common interface so that they all become easier to use.
For example, they all have similar File and Edit menus and some shortcut keys do the same in all applications.
COMMAND LINE
Powerful and fast.
Simple prompt screen.
Good example is MS-DOS®.
Quick and flexible.
Only useful if you understand how the system works.
Otherwise can cause drastic problems.
NATURAL LANGUAGE
Designed to understand human phrases.
Input may be through human speech.
Easy to use interface.
Intensive processing (makes slow).
People use different phrases to mean the same thing (ambiguity).
Good interface design
is important because it will...
o Be easy to use for inexperienced users
o Give information about what processing is happening
o Be consistent so that the user becomes familiar with it quickly
o Have facilities for more experienced users to customise the interface
o Always do as the user expects
o Be clear (everything should be obvious to the user)
o Reduce the possibility of mistakes by checking the user’s input
o Not require the user to remember many commands
System utilities are programs that perform specific functions (generally maintenance).
Some tasks that system utilities carry out include...
COMPRESSION
System utility programs convert data into a format that takes up far less memory space. Communication of data is faster when file size is reduced, and it is therefore particularly useful when data is being sent from one computer to another.
FILE CONVERSION
File extensions are related to specific applications. A utilities program enables applications to open a file with a different extension. e.g. MS Word can open a .wps file created by the word processor in MS Works even though its own files have an extension of .doc(x).
KEEPING CONFIGURATION FILES
These contain information on system parameters. When a program is run, it may need to look at configuration files to see which conditions it should adapt to.