E-R Diagram
E-R Diagram Entity-Relationship Diagram is a graphical representation of entities and their relationship to each others. It describes how data is related to each other. An entity is a piece of data- an object or a concept about which data is stored. A relationship is how the data is shared between entities. In E-R Diagram, there are 3 main Components:

E-R Diagram of a Hospital Management System

Data Flow Diagram
A Data Flow Diagram (DFD) is a graphical representation of the "flow" of data through an information system, modeling its process aspects. DFD is often used as a preliminary step to create an overview of the system, which can later be elaborated.

The purpose of data flow diagrams is to provide a semantic bridge between users and systems developers. The diagrams are: * graphical, eliminating thousands of words; * logical representations, modeling WHAT a system does, rather than physical models showing HOW it does it; * hierarchical, showing systems at any level of detail; and * jargonless, allowing user understanding and reviewing.

The goal of data flow diagramming is to have a commonly understood model of a system. The diagrams are the basis of structured systems analysis.

Data flow diagrams have the objective of avoiding the cost of: * user/developer misunderstanding of a system, resulting in a need to redo systems or in not using the system. * having to start documentation from scratch when the physical system changes since the logical system, WHAT gets done, often remains the same when technology changes. * systems inefficiencies because a system gets "computerized" before it gets "systematized". * being unable to evaluate system project boundaries or degree of automation, resulting in a resulting in a project of inappropriate scope.

Data Flow Diagram is denoted by using the symbols below;