many to one relationship: when more than one instance of an entity is associated with a single instance of another entity, then it is called many to one relationship.one to many relationships: when a single instance of an entity is associated with more than one instance of another entity, then it is called one to many relationships.one to one relationship: when a single instance of an entity is associated with a single instance of another entity, then it is called one to one relationship.A relationship set is a set of relationships of the same types. A relationship may also have a set of attributes called descriptive attributes. In an E-R diagram, derived attributes are displayed in dashed ovals.Ī relation is an association between two or more entities. Derived attributes: Derived attributes are the attributes whose values can be derived from the values of the other related attributes or entities.In an E-R diagram, multi-valued attributes are displayed in double ovals. Such attributes are called multi-valued attributes. In some cases, an attribute can have a set of values for the same entity. Such attributes are called single-valued attributes. Single-valued and Multi-valued attributes: Most attributes have a single value for a particular entity. Composite attributes are attached to their component attributes by straight lines. Composite attributes can form a hierarchy. Composite attributes can be divided into smaller subparts, which represent more basic attributes with independent meanings. Simple and Composite attributes: Attributes that are not divisible are called simple or atomic attributes.There are several types of attributes that occur in the ER diagram.
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