systems life cycle

• when an organisation or a client considers that one of its systems has problems or is in need of improvement a system analysis takes place.
• A system analyst studies the system to determine where the problems are and how the system can be improved.
• the systems life cycle can be summarised as : analysis, design, development and testing, implementation, documentation and evaluation / maintenance.
• system analyst is an IT specialist responsible for the life cycle of a new/ modified IT system, from analysing the problem to implementing an entire system.
• Systems life cycle are the different stages in the process of producing a new IT system.
• The analysis stage starts with the definition of the problem and a feasibility study. It involves looking at the problem with the client to find out the client´s requirements and needs.
• The analyst knows about the computer system and what is possible.
• IThe feasibility study is a report that states what is possible.
• When the feasibility study is accepted then the collection of information begins.
• the methods for collecting information or researching an existing system are: observation, interviews, questionnaires and document coolection.
• the aadvantages o observation is that it only involves the system analyst.
• the disadvantage of observation is that people tend not to act in a normal way when they know they are being whached.
• questionaries can be obtained a lot of peoples views in a short period of time.
• Questionnaries are less time-consuming but some people may not take them seriously.
• A disadvantage of document collection is that it is often difficult to understand and documents do not always reveal all of the processes and procedures about a system.
• Analysis collectinghas 3 stages:

  1. definition of the problem and feasibility study.

  2. collection of information and researching an existing system.

  3. requirement specification.
• The requirements specification is a list of what will be necessary in the solution.
• The requirements specification will include:

  what the organization wants the system to do.

  details about storage requirements.

  information about the desired hardware and software.
• The requirements specification list the things that after consultation, the organization has decided must be successfully done to satisfy them, and the analyst has agreed that this is what can be delivered.
• The requirment specification is going tto provide the RULES around which the final evaluation will be carried out.
• all computer system consist of input output processing and storage.
• The design stage consist of the output designs, input designs, data storage and the processing.
• The purpose of the design stage is to decide what the output will look like.
• The analyst's job is to produce a system that will do a particular thing.
• If a client likes the output they are likely to accept the whole solution.
• design what the output screens must look like and then produce what is known as a prototype.
• once the output has been designed, it is clear what the input should be and then is possible to design the input screens.
• The input screen should pass for the same prototyping process as the output screens.
• Not all input data will come from the input screens.
• In the input design, the analyst has to decide how the data will be collected and design a method of inputting it.
• validation routines are set up to ensure that the data is valid.
• some input validation routines include: Length check, type check, format check, presence check and check digit.
• length check: check if the length of the string is equal to the length of the string. Ex: a password may need to be 8 letters long.
• Type check: checks that is the correct type of data. Ex: is it numeric, string, etc...
• Format check: checks whether the data conforms to a specific format. Ex: date must be in dd/mm/yyyy
• Presence check: checks whether the field contains any value or not.
• Check Digit: used to validate credit card numbers by checking the last digit against an algorithm based on the other digits.
• The verification check will ensure that the data was correctly transferred into the system in the first place.
• when is known what the input and output will be it is possible to design the data storage.
• finally in processing it can be designed how the input data is processed to produce the outputs required.