Entity Relationship (ER) diagrams are drawn when designing a database system, After the systems specification, an ER diagram is drawn showing the conceptual design of the database, this diagram shows the type of information that is to be stored in the system and how these information associate with each other (e.g. one-to-one, one-to-many, etc).
ER Diagrams are simple and easy to understand, thus, this diagram can be shown and explained to user representatives for confirmation and approval.
use of er diagram
Entity-Relationship diagrams are useful for modelling data and the relationships between the data. They can be used when the constraints between data are relatively simple. They do not allow specification of interactions between the data or model how the data changes (there are no processes in Entity-Relationship). Entity-Relationship diagrams are most often used to model databases.
There are many such systems of diagrams used to aid program design (e.g. data flow diagrams, entity relationship diagrams, control flow diagrams, flowcharts).
ERD diagrams bus company
In software engineering, an Entity - Relationship model(ER model for short) is an abstract and conceptual representation of data. Entity-relationship modeling is a database modeling method, used to produce a type of conceptual schema or semantic data model of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created by this process are called entity-relationship diagrams or ER diagrams.learn more www.ngprakasam.hpage.com
An entity-relationship diagram of a grading system can be viewed by visiting this website at http://stackoverflow.com/questions/9486156/er-diagram-for-grading-system. There is information included with the diagram about the grading system.
ER diagrams often use symbols to represent three different types of information. Boxes are commonly used to represent entities. Diamonds are normally used to represent relationships and ovals are used to represent attributes.
ER diagrame shows the relationship among entities.
mandatory and optional
A relationship between instances of a single entity type is called a self-relationship or recursive relationship. This type of relationship occurs when an entity is related to other instances of the same entity type within the same entity set.
If you have a many-to-many relationship between two entities you create an intermediate entity between.Now, the relationship between the first entity and intersection entity is one-to-many, and the relationship between the second entity and intersection entity is one-to-many also.
Entity Relationship Diagrams (ERD's) are a way of diagrammatically showing entities in an organisations and how they relate to each other. ERD's show detailed representations of the information that is used in a system and how it relates to other data. There are a number of symbols that represent the entities and the relationships between them; the relationship can be a one to many relationship, many to many or one to one.
ENHANCED ENTITY RELATIONSHIP OR EXTENDED ENTITY RELATIONSHIP