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An ER Diagram
Entity Relationship Diagram NotationsPeter Chen developed ERDs in 1976. Since then Charles Bachman and James Martin have added some sligh refinements to the basic ERD principles.
Entity
An entity is an object or concept about which you want to store information.
Learn how to edit text on an entity.
Weak Entity
A weak entity is an entity that must defined by a foreign key relationship with another entity as it cannot be uniquely identified by its own attributes alone.
Learn how to edit text on this object.
Key attribute
A key attribute is the unique, distinguishing characteristic of the entity. For example, an employee's social security number might be the employee's key attribute.
Multivalued attribute
A multivalued attribute can have more than one value. For example, an employee entity can have multiple skill values.
Derived attribute
A derived attribute is based on another attribute. For example, an employee's monthly salary is based on the employee's annual salary.
Relationships
Relationships illustrate how two entities share information in the database structure.
Learn how to draw relationships:
First, connect the two entities, then drop the relationship notation on the line.
Cardinality
Cardinality specifies how many instances of an entity relate to one instance of another entity.
Ordinality is also closely linked to cardinality. While cardinality specifies the occurences of a relationship, ordinality describes the relationship as either mandatory or optional. In other words, cardinality specifies the maximum number of relationships and ordinality specifies the absolute minimum number of relationships.
Click here for more cardinality notations
To learn how to express cardinality in SmartDraw, click here.
Recursive relationship
In some cases, entities can be self-linked. For example, employees can supervise other employees.
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Example er diagram for hospital?
how to draw e-r diagram for hospital management system plz show the figure?
What is ER diagram for timetable management system?
An ER diagram is an "Entity Relationship" diagram, which illustrates the relationships between the entities in a data model. A data model for a timetable management system might have entities like Days, Periods and Rooms. Its ER Diagram would then show that a Day is broken down into multiple Periods, and each Room might be used for multiple Periods.
What are the differences between EER diagrams and ER diagrams?
Extended ER diagram is a variant of ER diagram. EER include ER diagram + hierarichal concept. Extended ER diagram is also called Enhance ER diagram(EER).
Entity relationship model with example?
draw an er diagram on attendance management system
Drow a er diagram of a supermarket?
supermarket (ER-Diagram)
Er model.... Entity relationship diagram about how patient sets appointment to a doctor for check up....?
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How can you make Er diagram of online shopping?
Er diagram of on line shopping
An ER diagram for a website?
I 'm need ER diagram for websit news
Where can you find an ER diagram on online shopping?
ER Diagram of online shopping
How do you draw a ER diagram for an automobile industry?
How do you draw a ER diagram for a automobile industry?
How do you draw the ER Diagram for online tour site?
draw the er diagram for tours
How do you draw the ER diagram of bus reservation?
You also can draw your ER diagram by so many ways. A software called Edraw is a better software to draw the ER diagram. This one has some ready-to-use ER diagrams templates conceptdraw.com/How-To-Guide/er-diagram
