Many-to-one − When more than one instance of entity is associated with the relationship, it is marked as 'N:1'.
The following image reflects that only one instance of entity on the left and more than one instance of an entity on the right can be associated with the relationship.
One-to-many − When more than one instance of an entity is associated with a relationship, it is marked as '1:N'. The following image reflects that only one instance of each entity should be associated with the relationship.
One-to-one − When only one instance of an entity is associated with the relationship, it is marked as '1:1'. Cardinality is the number of instance of an entity from a relation that can be associated with the relation. Binary Relationship and CardinalityĪ relationship where two entities are participating is called a binary relationship. All the entities (rectangles) participating in a relationship, are connected to it by a line. Name of the relationship is written inside the diamond-box. Relationships are represented by diamond-shaped box. Multivalued attributes are depicted by double ellipse.ĭerived attributes are depicted by dashed ellipse. That is, composite attributes are represented by ellipses that are connected with an ellipse. Every node is then connected to its attribute. If the attributes are composite, they are further divided in a tree like structure. Every ellipse represents one attribute and is directly connected to its entity (rectangle). Attributes are represented by means of ellipses. AttributesĪttributes are the properties of entities. Rectangles are named with the entity set they represent. EntityĮntities are represented by means of rectangles. Any object, for example, entities, attributes of an entity, relationship sets, and attributes of relationship sets, can be represented with the help of an ER diagram. Let us now learn how the ER Model is represented by means of an ER diagram.
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