Data Models
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This document discusses data models and the entity relationship model. It defines a data model as a representation of real world objects and events that hides low-level storage details. The entity relationship model represents entities as objects with attributes, and relationships between entity sets. Entities are grouped into entity sets and represented as rectangles. Relationships are represented as diamonds connected to entity sets. Attributes are represented as ellipses connected to entity sets. The document describes key attributes, simple attributes, composite attributes, derived attributes, and single and multi-value attributes. It provides an example of a student entity with attributes like roll number, name, and date of birth.
Data Models
- 2. Data Models • A Model is a representation of reality, ‘real world’ objects and events, associations. • Data Model is a collection of high level concepts that can be used to describe the structure of a database that hide many low levels storage details. • Data Model can be defined as an integrated collection of concepts for describing and manipulating data, relationship between data, and constraints on the data in an organization.
- 3. The Entity Relationship Model (ER Model) • Entity–Relationship modeling was developed for database and design by Peter Chen in 1976 • Entities are things or an object in the real world that is distinguishable from other objects based on the values of the attributes is posses. • Entities are described in a database by a set of attributes. For E.g. Student is an entity which has attributes like RollNo, Name, DateOfBirth. • An entity set is a collection of same type of entities that share same attributes. • Relationship is an association among several entity set. For E.g Student is “admitted” to a single branch (Computer , Electronics etc.)
- 4. Entity, Entity-Set and Attributes Student Table Roll_No Name Date_Of_Birth 1 Ajay Joshi 12/3/2000 2 Poonam Sharma 28/4/2000 3 Vinay Deshmukh 29/12/1999 Attributes Entity Set Entity
- 5. ER Diagram • ER Model is represented by using ER Diagram. • Entity Set is represented by “Rectangle” • Relationship is represented by “Diamond” • Attributes are represented by “Ellipses” • Linking of attributes to entity sets and entity sets to relationships is by “Lines” Branch Student Admitted DateOfBirth Name RollNo Id BName
- 6. Types Of Entity Set Strong Entity Set : An entity set that contains sufficient attributes to uniquely identify all its entities. Weak Entity Set: An entity set which does not have sufficient attributes to uniquely identify all its entities. Account Logs Transaction
- 7. Types Of Attributes There are many types of attributes which are as follows: Key attribute Composite attribute Derived attribute Single-value attribute Multi-value attribute Simple attribute
- 8. Key Attribute This attribute has the unique value for an entity which is used to identified given row in the table is called as key attribute of an entity. It is represented by underlying the attribute name. Student Roll_No
- 9. Simple Attribute Simple attributes are atomic values, which cannot be divided further. For example, a student’s phone number is an atomic value of 10 digits. It is simply represented by an oval. Student Roll_No PhoneNo
- 10. Composite Attribute Composite attributes are made up of more than one simple attributes. For example , a student complete name may have F_Name, M_Name and L_Name. Student RollNo PhoneNo Student_Nm F_Name M_Name L_Name
- 11. Derived Attribute Derived attributes are the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database. For example age can be derived from DateOfBirth. It is represented by dashed oval. Student RollNo PhoneNo DateOfBirth Student_Nm F_Name M_Name L_Name Age
- 12. Single-value and Multi-value Attribute • Single-value attributes contain single value. For example Aadhar_card-number • Multi-value attribute may contain more than one values. For example a person can have more than one phone number, email_address etc. It is represented by double oval. Student RollNo PhoneNo DateOfBirth Student_Nm F_Name M_Name L_Name Age
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