2011年3月26日星期六

Tutorial Blog 3 : Entity-Relationship Diagrams & Data Flow Diagrams

Let's talk about Entity-Relationship Diagrams and Data Flow Diagrams this week.Entity-Relationship Diagrams and Data Flow Diagrams are two tools that a systems analyst uses for process modeling.
Entity-Relationship Diagrams( ERD) is a tool that  shows the connections among entities in a system.For example,  a university have student, classroom, instructor, and grades entities. On the ERD, each relationship describes a connection between two enities. I have created a diagram shown below, let's break it down in details about how the flow goes.



In the picture that I created, a class may contains one or more students, those students are taught by a specific instructor, and may or may not be held in a classroom. A student may or may not take classes in a given semester, and may or may not earn a grade. It is important that the system analyst has an understanding of the system. They will review the ERD with the users. After the users approve the ERD, the systems analyst checks data items associated with student entity and identifies data items such as Student ID, Address, Phone #, Contact Information and Photo.
A Data Flow Diagram( DFD) is a tool that shows the flow of data in a system. There are four key elements of DFD the data flows, the processes, the data stores, and the sources.Let's take a  look of the diagram that
I've created and shown below. I will deifne each element in detail in just a second .


OK. First of all,  a data flow, indicated  by a line with a arrow and express the input or output data or the specific information into or out from a process.A process is drawn as a circle, it transforms an input data flow into an out data flow.A data store is shown as a rectangle with no sides, it is containing a place for data and information.A source is shown as a rectangle with sides, it identifies an entity outside the scope of the system and receives information from the system and then sends data into the system.
I hope after reading this tutorial, everyone of you will get a better understanding of what  the Entity-relationship diagrams and data flow diagrams are. Moreover, when someone ask u what are these two diagrams, you are able to teach and explain in detail to them.


work cited
Shelly, Gary and Misty Vermaat, Discovering Computers 2010, Boston, MA: 2010 Course Technology, 2010

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