Presentation on Entity Relationship Diagram.pptx

Entity Relationship Diagram presentation

1. Presentation on Entity-Relationship diagram

2. Entity Relationship Model Entity Relationship Model is a logical representation of data in an organization . OR A semantic data model, used for the graphical representation of the conceptual database design It is used to describe the elements of a system and their relationship. It was introduced be peter Chen in 1976.

3. Entity Relationship Model Advantages of E-R Model Conceptual simplicity Visual representation Effective communication tool

4. Entity Relationship Model Major Components Entities Attributes Relationships

5. Entity Relationship Model Entities An entity is a person, place, thing or event for which data is collected and maintained. For Example, a library system may contain data about different entities like BOOK and MEMBER. A college system may include entities like STUDENT, TEACHER, COURSE and CLASS etc.

6. Entity Relationship Model Some examples of entities are as follows. Person: TEACHER, PLAYER, DOCTOR Place: COUNTRY, CITY Object: VEHICLE, TOY, FURNITURE Event: PURCHASE, ADMISSION, REGISTRATION Concept: ACCOUNT, PROGRAMMING The entity is used in three meanings that are as follow

7. Entity Relationship Model Entity Type   It is  collection of entity  having common attribute. All entities in an entity type share common characteristics. It is also Known as entity class. For Example , STUDENT entity class is a set of all students.

8. Entity Relationship Model Entity Instance An entity instance is a  single occurrence of an entity . For Example , a student Abdullah of STUDENT entity type is an entity instance.

9. Entity Relationship Model Entity Set A set of all entities of a particular entity type in the database at a given point of times is called as entity set. For Example , an entity set student may consist of all student in the university.

10. Types of Entities Types of Entities The following are the types of entities in DBMS Strong Entity The strong entity has a primary key. Weak entities are dependent on strong entity. Its existence is not dependent on any other entity. Strong Entity is represented by a single rectangle −

11. Types of Entities Weak Entity The weak entity in DBMS do not have a primary key and are dependent on the parent entity. It mainly depends on other entities. Weak Entity is represented by double rectangle −

12. Types of Entities Example of Strong and Weak Entity The example of strong and weak entity can be understood by the below figure.  The Strong Entity is  Professor , whereas  Dependent  is a Weak Entity.

13. Elements of E-R Model Attributes  describe the characteristics or properties of an entity in a database table. An entity in a database table is defined with the ‘fixed’ set of attributes. For example, if we have to define a student entity then we can define it with the set of attributes like roll number, name, course. The attribute values, of each student entity, will define its characteristics in the table.

14. Entity-Relationship Diagram Attributes Entities has attributes, which can be considered as properties describing it, for example, for  Teachers  entity, the attributes are   Teacher_Name, Teacher_Address, Teacher_Subject , etc. The attribute value gets stored in the database.

15. Entity-Relationship Diagram Multivalued Attribute An attribute that has multiple values for a single entity at a time is called a Multivalued Attribute. For example, technical skills of a student that can be programming, web development, etc.

16. Entity-Relationship Diagram Composite Attribute If an attribute has two or more other attributes, then it is called a Composite Attribute. For example, Student Name can be divided as Student First Name, Student Middle Name, and Student Last Name.

17. Entity-Relationship Diagram Derived Attribute As the name suggests, the derived attribute is an attribute whose value can be calculated from another attribute. For example, Student Age can be derived from Date-of-birth of a student.

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