What is ellipse in ER diagram?
Every ellipse represents one attribute and is directly connected to its entity (rectangle). If the attributes are composite, they are further divided in a tree like structure. Every node is then connected to its attribute. That is, composite attributes are represented by ellipses that are connected with an ellipse.
What a dotted ellipse indicates in ER diagram?
Derived Attribute for any Entity Derived attributes are those which are derived based on other attributes, for example, age can be derived from date of birth. To represent a derived attribute, another dotted ellipse is created inside the main ellipse.
What are the symbols used in ER model?
2.3 ER Diagram Attribute Symbols
| Name | Description |
|---|---|
| Attribute | A basic attribute is represented by a single oval with its name written inside. |
| Key Attribute | This is a special attribute that is used to uniquely identify an entity. It is represented by an oval with its name underlined. |
What does a ellipse represent?
Ellipse is an integral part of the conic section and is similar in properties to a circle. Unlike the circle, an ellipse is oval in shape. An ellipse has an eccentricity less than one, and it represents the locus of points, the sum of whose distances from the two foci of the ellipse is a constant value.
What is represented by an underlined ellipse in ER model?
A double ellipse represents Multi-valued attribute in ER-diagram. Symbols of ER Model. Strong Entity has its own attribute. They will also have a primary key, distinguishing each occurrence of the entity.
What is the purpose of diamond symbol in ER diagram?
In the ER diagram the relationship between two strong entity set shown by using a diamond symbol. The relationship between one strong and a weak entity set shown by using the double diamond symbol. The connecting line of the strong entity set with the relationship is single.
What is weak entity example?
A weak entity is one that can only exist when owned by another one. For example: a ROOM can only exist in a BUILDING. On the other hand, a TIRE might be considered as a strong entity because it also can exist without being attached to a CAR.
What are Notations of ER diagram?
ER diagram notations and symbols. Similar to other diagram shapes, in ER diagrams entities are represented with rectangles, attributes are represented by ovals or inside entities, and relationships are shown in diamonds or with lines. There are six notation types, some more common than others.
What does triangle represent in ER diagram?
Pyramid diagrams help you visualize information as a triangle divided into horizontal slices. Labelled slices represent a hierarchy. Pyramids are used in marketing presentations to show and analyze hierarchy levels.
What are the three components of ER models?
ER diagrams or ERD’s are composed of three main elements: entities, attributes, and relationships.