02-07-17 cheapnisha 0 comment


Entity Relationship Model

TIME TRACKING DATABASE SYSTEMEntity relationship diagram represents the data entities and their association with other data entities in database so that diagram of inter relationship can be used to perform business activities. It gives concept of data arrangement and relations in database development. Al though, ER diagram does not define any operation to perform in business prospective but gives basic idea of data model in which data is arranged to meet business operations. Entities have identification with the attributes.

Components of ER Model

Entity: Smallest and atomic values in database relations are entity which is real world objects. Entities are represented with the help of rectangle diagram. School, mobile, watch etc are example of entities (Teorey.et.al.2011).

Attribute: Entities are identified with their properties which is called attribute. Oval shape in ER diagram represents attributes. Attribute may be of following types:

  • Key attributes: Attribute in database those are capable to identify the entire record form table are key attributes. For example, roll number and mobile number may be key attribute to identify record from tables.
  • Composite attributes: attributes those have composite values in columns are called composite attributes. For example name of student is composite in nature and can be transformed to atomic attributes as first name, middle name and last name.
  • Derived attribute: Attributes those are derived from other attributes are called derived attributes. For example, age can be derived from date of birth column.

Relationship: how to entities are interdependent to other entities in other tables of database are determined with help of relationship diagram. Relationship may exist in three forms:

  • One to one relationship (1:1): In it, one entity of table has relation with other one entity in another table. For example, one monitor in one class is one to one relationship (De Simone.el.al.2010).
  • One-to-many relationship (1: M): Relationship of one entity with more than one entities in another table is one-to-many relationship. For example, one class can contain more than one student.