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
An entity relationship diagram (ERD) represents the entities, or groups of information, and their relationships maintained for a business. An entity relationship diagram represents the entities, or groups of information, and their relationships maintained for a business. An entity relationship diagram represents the entities, or groups of information, and their relationships maintained for a business.
Entity relationship (ER) diagram, in software engineering is a graphical representation of describing data base in a systematic way. The main components of ER are the entities of the model and the relationship that exist between these.
The entity relationship diagram is a representation of business rules that applies to a company's data. It is an excellent communication tool that guides about the business requirements and assist the architecture and design team about the physical data base design.
A completed ER diagram is the actual blueprint of the database. Its composition must reflect an organization's operations accurately if the database is to meet that organization's data requirements. It forms the basis for a final check on whether the included entities are appropriate and sufficient, on the attributes found within those entities, and on the relationships between those entities. It is also used as a final crosscheck against the proposed data dictionary entries. The completed ER diagram also lets the designer communicate more precisely with those who commissioned the database design. Finally, the completed ER diagram serves as the implementation guide to those who create the actual database. In short, the ER diagram is as important to the database designer as a blueprint is to the architect and builder.
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
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
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.
It is used to resolve Many-to-Many relationship.