Data Flow Diagrams

A data flow diagram (DFD) is a graphical representation of the "flow" of data through an information system, modelling its process aspects. Often they are a preliminary step used to create an overview of the system which can later be elaborated.DFDs can also be used for the visualization of data processing (structured design).

A DFD shows what kinds of data will be input to and output from the system, where the data will come from and go to, and where the data will be stored. It does not show information about the timing of processes, or information about whether processes will operate in sequence or in parallel (which is shown on a flowchart).

System Flowchart

What is a System Fowchart?
System flowcharts are a way of displaying how data flows in a system and how decisions are made to control events.
To illustrate this, symbols are used. They are connected together to show what happens to data and where it goes. The basic ones include:

Symbols used in flow charts
Note that system flow charts are very similar to data flow charts. Data flow charts do not include decisions, they just show the path that data takes, where it is held, processed, and then output.

Flowchart

What is a Flowchart?

A flowchart is simply a diagram which shows the breakdown of a task or system into all of the necessary steps.

Each step is represented by a symbol and connecting lines show the step-by-step progression through the task.

Have a look at the diagram below. It shows the process of ordering a burger.

There is a clear start, a series of steps, a clear direction of flow and a clear end or finish point.

This is a very simple flowchart. For some tasks or systems, the flowchart can be very complex and detailed.

System Design

We have discussed before about the first stage of the system life cycle, which is the system analysis. And based on the user requirements and the detailed analysis of a new system, the new system must be designed. This is the phase of system designing. It is a most crucial phase in the development of a system. Normally, the design proceeds in two stages :

preliminary or general design
Structure or detailed design
Preliminary or general design: In the preliminary or general design, the features of the new system are specified. The costs of implementing these features and the benefits to be derived are estimated. If the project is still considered to be feasible, we move to the detailed design stage.

Structure or Detailed design: In the detailed design stage, computer oriented work begins in earnest. At this stage, the design of the system becomes more structured. Structure design is a blue print of a computer system solution to a given problem having the same components and inter-relationship among the same components as the original problem. Input, output and processing specifications are drawn up in detail. In the design stage, the programming language and the platform in which the new system will run are also decided.

There are several tools and techniques used for designing. These tools and techniques are:

1-Flowchart
2-Data flow diagram (DFDs)
3-Data dictionary
4-Structured English
5-Decision table
6-Decision tree

Benefits:
1-Improved system performance; individually tailored configuration advice demonstrates where improvement is necessary, and how to improve the system to regain lost performance.

2-Customers gain a detailed understanding of how their users use their system. This Usage Profile can be leveraged to develop future architecture changes.

3-Potential to learn of future concerns, allowing customers to take proactive measures to avoid problems.

4-A baseline performance level is established against which benefits can be compared and changes to the system predicted or foreseen.

System Analysis

System analysis is the process of examining an existing system in detail, in simple terms analysis is to see what data comes in to the company, how it is processed and and what outputs they produce.The purpose of analysing the system is to see how data flows around the system. In particular the process of system analysis requires:

1-Collecting information on how the existing system works.
2-Establishing its inputs, outputs and processing.
3-Recording information, for example in the form of data flow diagrams.
4-Identifying problems.

As we have mentioned the first stage of system analysis is collecting information,and there are four methods of doing this:

1-Examination of documents
Examining all the documents within a system for example, bills, invoices, letters, order forms, payslips etc.

2-Questionnaires
The most common way of gathering information. It is a printed sheet given to the employees, which contains questions for them to answer about the system. For example, what details of the worker and their pay would you like to see on your worker's payslips?

3-Interviews
Preparing an interview with an employee on certain date, to discuss them about the system. But most probably employees will give false information.

4-Observation
Observing and having a look on the how the employees work, but most employees won't feel comfortable with this, and others might give wrong impressions while being observed, and so the analyst will get wrong information.

Activity 12 Page 13

I recently visited Ebay, which of course you might know. Ebay's main purpose is creating an online market, where goods are sold and bought between the buyer and the seller. There is also auctions in Ebay, like for any product you place a bid to buy the product at a certain price then if another one is also interested in buying that product he places a higher bid and so on, until someone places a bid which no other will placer a higher one he'll get that product. Or you can buy the product immediately but in a much higher price.

SMS

Invitation normal form:
Hello everybody, there is a party next thursday in my house starting from 5.00.So i hope you all come.

Invitation SMS form:
Hi evrybody, theres a prty nxt thursday in my house strting frm 5. so ihope u all come.