Keys in ER diagramsĪ key is an attribute in ER diagrams whose values are distinct for each individual entity in an entity set.įor example for a student entity set Roll Number or Registration Number can be a key because these are unique for each student entity. Derived attribute is represented by dashed or dotted outline ovals in the ER diagram. You may have seen many times while filling an online form that on filling Date of Birth, Age is automatically calculated. It can be derived from Date of Birth attribute and current date. So we can keep this attribute in database as derived attribute. For example age attribute of a person changes from time to time. The attributes whose values can change over time and can be derived from the stored attributes are called Derived Attributes. These are represented as ovals with single outline in ER diagram. Date of Birth and Basic Pay are examples of Stored Attribute. The values in Stored Attributes can be used to derive values for other attribute. The attributes whose values are stored in database and which does not change over a period of time are called Stored Attributes. On the Basis of How the Attribute Value can be Stored 1. These are not simply included as a column in an entity relation. In relational database a separate table is created for multi valued attributes. Multi valued attributes are represented with double outlined ovals in ER diagrams. For example a person can have multiple Phone Numbers, E-mail Ids, Addresses, Qualifications, Job Experiences. Multi valued attributes can have more than one value at a given instance of time. These are represented by single outline ovals in ER diagram. For example Date of Birth, Roll Number, Father’s Name attributes can have single value. Single valued attributes can have only one value at a given instance of time. On the Basis of Count of Values that can be Stored 1.
Composite attributes are represented by an oval connected with other attribute ovals in an ER diagram.
TERRAER DERIVED ATTRIBUTE ZIP
Address attribute is usually divided into House Number, Street, City, State and Zip Code. For example Name attribute can be divided into First Name, Middle Name and Last Name. Composite AttributesĪttributes that can be further divided and represented into simple attributes are called composite attributes. Simple attributes are represented by oval with single outline in an ER diagrams. Each student entity will have a Roll Number that may store a single numeric or alphanumeric value. Simple AttributesĪttributes that have only atomic values are called simple attributes. Types of Attributes On the Basis of Composition 1.
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