We’ll continue our discussion on process modeling. In the previous lecture, we talked about functional decomposition as a first step in process modeling. Given the complex process, we should try to decompose it into sub-processes or smaller processes which can be better understood in terms of what actions they do.
Data Flow Diagrams
We’ll now continue with the process modeling and look at another important tool called Data Flow Diagrams. Data Flow Diagrams are a very popular tool for describing functions which are required in a given system. And these functions are specified in terms of processors as well as the data used by these processes. So this is one important difference from function decomposition diagram where we do not show data explicitly whereas in the case of Data Flow Diagrams both the processes and the data which will flow among those processes would be shown. That’s why they are called Data Flow Diagrams.
We may do function decomposition diagrams before doing data flow diagram. However we may also do data flow diagrams directly but it is better to think about function decomposition beforehand and it would be a good practice to do function decomposition before, because this function decomposition would be anyway required when we do data flow diagrams. So having done it earlier before coming to data flow diagrams would always be more fruitful. Data flow diagrams have more content than function decomposition diagrams obviously because now we will be explicitly showing the flow of data.
Data flow diagrams are very simple pictorial tools. They represent the functional and the data flow in the form of a diagram. And therefore they are very easy to understand by all people, users as well as managements. So they have become very popular in the analysis phase for representing the functions performed by a particular application.
Data flow diagrams are also unambiguous and concise. They can describe processing both at the physical level as well as at the logical level. Remember that at physical level we describe the way things are done rather than what needs to be done. So we can have both data flow diagrams. In fact, usually when you’re studying the existing system, you are studying it at the physical level. Therefore if you represent these in the form of a data flow diagram, the diagram will be at the physical level representing both what is done and how it is done currently.