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System Development Life Cycle

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Will Leung

on 11 June 2013

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Transcript of System Development Life Cycle

Top-down design: This is breaking down the problem into smaller components so that further break down can be done.
Definition: This stage is about finding and solving problems within the existing system by collecting and examining data from it
System development life cycle
The 5 Methods of Analysis
Interview
Questionnaire
Study existing documents
Literature search
Observation
What is the output of this stage?

The output of this stage is a plan to build and sell a system. This system however is just an idea , it will have to be programmed ,tested and made user friendly before people can buy it
Analysis
Data collection identifies
- Who inputs data to the system
- What form the data is in
- Any validation that is needed
- What processing is done to produce the required outputs
Questionnaire: Getting people to participate in surveys about your products you know what improvements can be made.
+ Easy to reach people
- people don't respond and contribute
- people don't get to express their answers as precisely
This must be carried out in a thorough and systematic way or some vital aspect of the system may be overlooked.
Design
Operation
Installation
Maintenance
Interviewing: Obtaining detailed data by recording what people answers.
+ Detailed, easy to record
- Can be time consuming
- Data may be difficult to be grouped.
Studying existing document: Get existing information and get help from there
+ Very efficient if some parts are not needed to be changed
- Some existing documents do not tell in detail
Literature searching:
+ Can save effort if the used piece is solved
- Details of their solutions may not be provided
Observation: Getting people to explore by their visual sights.
+ Answers are less likely to be biased
- Can be time consuming
What is Prototyping?
Library System
Client Data System
Book Data System
Loans and returns
Each module might be required to update the files, therefore these module need to be break down further more. "Stepwise refinement"
Client Data System
Edit Client Details
Delete a Client
Add a client
Add a Client
The purpose of prototyping is to test out the system if it works
properly. Developer can use prototype to look for improvements and errors.

*It is not a full version of the software but developer can edit it.
Obtain Client Details
Attempt to insert in client file
Confirm Success/Fail
Efficiency of solutions
A file of records stored as number of bytes, this helps us to estimate the storage required.
But we have to know clearly how many bytes are stored for each data type
Integration
Development
Parallel Running
Social Implications
Economic Implications
More work for the employees or they may have to work longer hours to cope with the extra work
This is where the two software's (old and new) run at the same time and once both software's have been working together for a while the old system will be replaced
Staff may have to be paid more or extra staff employed. However a new system could make a business benefit , in fact mistakes less critical for the business
Phased Introduction
With Phased Introduction parts of the software will be implemented at different times.
Social significance and implications of the widespread use of computers
Social Implications
Economic Implications
Principles
Consequences
More hours to work in this case also. Different people may be affected in different times - could cause dissatisfaction.
Data searching and sorting are parts of the development stage in operation phase. Next one being programming errors occurring, listing:

Exceptions of codes being allowed or not depending on the rules.
Cost may be associated with extra work. The Changeover takes longer; difficulties with system may become drawn out - the company's reputation for efficiency may suffer
Direct Changeover
OECD- principles should be apply to data held by people
What is Maintenance:

The definition for maintenance is to maintain software qualities by keeping it up to dates and giving it changes after the software is delivered to the users and or customers. Is heavily reliant n previous stages (design, analysis etc.) Can be very time confusing and cost effort and money.
Direct changeover is when the old software is completely and immediately taken over by the new system
Social Implications
Economic Implications
Staff may feel under great pressure/stress during this type of changeover. Customers may also dislike changes - at least initially.
As with the other methods there are training costs to be considered. the costs of hardware/software may also have ti be paid at one time rather than spread out over time. Always a risk of failure turning away potential customers
Consists of 4 main types:
Corrective maintenance - fixes bugs and residual errors that can be found in coding, design logic errors and such
Adaptive maintenance - Adapts the software to environments by making it compatible to run on hardware and in operating systems
Perfective maintenance - updates the software based on the changing user requirements and standards
Preventive maintenance - updates documentations to inform about changes.

2.Algorithms ( operations needed in the program):
formulas or procedures that can be mathematical,
used to solve a 'recurrent' problem.
Made by
Alessandro; Alissa
Allard; RICH
Will; League of legends
Chansu; CSFree
JT; Just JT
Factors affecting systems’ maintainability:
Factors that can decrease maintenance effort:

Use of structured techniques
Use of modern software
Use of automated tools
Use of database techniques
Good data administration
Experienced maintainers
Traditional maintenance
Evolutionary maintenance or software evolution

Logic errors are non-intentional ones that are usually caused by design flaws ,like multiplying a number when the programmer is meant to square it, displaying wrong message
Syntax errors being errors because of program rules disallowing, known as the ‘grammar errors’ of programming languages , such as misspelled variable names like ‘innt’ when it should be ‘int’, missing semicolon at the end of a line.


Runtime errors happen when the computers are asked to perform something they can’t , like when dividing a variable by 0 which gives no answer, trying to open a file that does not exist
Runtime Errors
Logic Errors
Economic Consequences
Political Consequences
Parallel Running
Cultural Consequences
Syntax errors
Environmental Consequences
What are the consequences of social significance and implications of the widespread use of computers?
Look for the inputs, outputs and processes:
will the System interact with peripherals like mouse or web cam ?
will the program be able to save data or to respond to the mouse click or to keyboard pressing?

Identifying problems:
For example our system may not be user friendly or it could have problems with the laws in some countries and needs to be modified.

New system requirements specification:
some arguments in our program may interfere with the Operating System
or it may need too much RAM to work.

Hardware and software needed:
some computers may not support our program, or the software may become obsolete in less time then we expected
What will be done?
What is the output of this stage?
This stage outputs a program that works , but it isn't use friendly yet
this is the part where the system is made
Documentation
System Documentation
Modular Design
This type of documentation is usually for programmers who needs to know the parts in the program. Therefore, the program can maintained and improved .
For example it could be in a hurry and the programmer needs read the documentation and change some parts. It would help a lot if the documentation is present.

There are some methods to make the code more understandable:
-Meaningful identifier names
-Keep methods small
-Good code structure

Details should be provided:
-Purpose of the program, data flow, structure
-Hardware and software
-Description of the purpose of each module, data structures used and also in pseudocode
-List of variables
-The test plan
Evaluation of the system
Data requirements
Advantages
of
Prototyping
In this stage of the system's development cycle, the system will be installed and therefor replace the ol system. There are a number of ways to implement the new system: Direct changeover, phased introduction and parallel running
There several information that we have to get before creating a program:
Some of the questions we have to ask ourselves are:

Compatibility with peripherals
Does the software use any peripherals? (web-cam, mouse...)

Does the software support input devices ? like bar code reader, micro
(magnetic ink character recognition )
Designer creates
diverse prototypes
1. Data types
For example - Integer
- Boolean
Users offer
concrete feedback
to designer
User Documentation
This is for non-technical users to run the program. So the internal structure shouldn't be shown in this type of documentation.

This should include:
-How to install the program, how to use it
-Troubleshooting guide to assist users
-Installation requirements (hardware and software, OS)
-Idea of input and output should be shown so the users knows what is expected to happen
An economic consequence of using computer systems in factories is that it causes unemployment in countries. A huge change that has been made is the way we communicate with each other, no longer do we need to be in the same place to do a business meeting because we can use telecommunication.
Designer
make changes
on his project
The OECD (Organisation for Economic Cooperation and Development) has created a number of principles which can be found later on in the presentation. The principles can by found on frame 43
Final draft of project
- Time is not wasted because changes are made in the beginning of the project
- Money saved as early changes are not
costly as late changes
The growth of computer system has affected the spread of the English language. With language comes culture, so this way peoples culture may change because of the computer systems.
Some people think that teenagers spend to much time playing computer games. Which isn't something you would want, but the internet also allows people to learn about new cultures through the use of chat rooms
- Provide more accurate solutions that the user
desires with the project
The first cycle has ended, please keep going around for the next system development......
This is mainly because the software will need to be supported by hardware. For example, a VOIP system will need some sensors or a web- cam. However, this part of the system development life cycle only requires to find out the parts needed, not to program the actual system.
If we assign 25 characters for the FORENAME and SURNAME fields
We can calculate the size of one record
By using this method,
- It allows us to know where to store it
- Capacity of RAM required to operate

After knowing the size, estimated of time can be calculated
Computer scientists often compare the storage and speed requirements of algorithms using big O notation. In a given high-level language, we can predict the storage required by a file of records.
Let's say that there are 1000 students to calculate their information
Based on the data table, we can easily create a formula of

1000 x 62 = 62000 bytes or 62 KB
Number of students
File size per student
However, these days, of course, the amount memory is very tiny
This shows how the show systems run together and at one point the new system replaces the old system
This shows how the new system immediately replaces the old system
By Chansu
- There should be limits to collect personal data
- Data should be obtained by the law of its data subject
- Data should be relevant to the used of purpose
- Accurate, complete and up-to-date
- Data collection should be specify as no longer than limit time
- Purpose of data use should be specified
- Personal data should be available
- Used for purpose which haven't be specified in the “Purpose specification principle”
- Personal data should be safely secure
- A policy with respect to personal data
- Should be available for establish
- Individual can get data from data controller
- Needs to confirm if there is data relates to the individuals
- Data controller should be in charge of keep track of data held by the principles stated above
This shows how the old system is broken down in and replaced in pieces by the new system
Changeover: the replacement of an old system with a new one
Collection limitations principle
Data quality principle
Purpose specification principle
Use limitation principle
Security safeguard principle
Openness principle
Individual participation principle
Accountability principle
System size because of the learning curve for programmers.
System age because their size grow, while their organisation becomes worse because it gets harder to understand.
Item number for input and output data affects the time needed to modify.
Different application type base on their purpose or program functions.
Different programming languagerequires the right people to understand and modify codes.
And degree of structure shows a systems organization.
if the system is not environmentally friendly it may cause problems
instead of solving them , this may include the waste of resources.
Full transcript