Database
- 2. Presentation Topic E-R Diagram Presented By: Mubeen Kiran
- 3. Objective What is E-R Diagram? What is entity? Types of entities What is Attributes? Types Of Attributes
- 4. What is E-R Diagram? An entity relationship model, also called an entity-relationship (ER) diagram, is a graphical representation of entities and their relationships to each other, typically used in computing in regard to the organization of data within databases or information systems. An entity is a piece of data-an object or concept about which data is stored.
- 5. Entity An entity can be a real-world object, either animate or inanimate, that can be easily identifiable. For example, in a school database, students, teachers, classes, and courses offered can be considered as entities. All these entities have some attributes or properties that give them their identity. An entity set is a collection of similar types of entities. An entity set may contain entities with attribute sharing similar values. For example, a Students set may contain all the students of a school; likewise a Teachers set may contain all the teachers of a school from all faculties. Entity sets need not be disjoint.
- 6. Types of Entities .Weak entities & Strong Entities .Associative Entities
- 7. Weak Entities In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key. The foreign key is typically a primary key of an entity it is related to. Strong Entity An entity set that has a primary key is called as Strong entity
- 8. Associative Entities Associative is a type of entity that associate the instances of one or many entity type with one another. The Attributes associative represent the relationship between the entity instances.
- 9. Attributes Entities are represented by means of their properties, called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes. There exists a domain or range of values that can be assigned to attributes. For example, a student's name cannot be a numeric value. It has to be alphabetic. A student's age cannot be negative, etc
- 10. Types Of Attributes 2.Composite attribute 3.Derived attribute 4.Single-value attribute 5.Multi-value attribute 1.Simple attribute
- 11. Simple attribute Simple attributes are atomic values, which cannot be divided further. For example, a Person Can have Only One gender and one date of birth.
- 12. Composite attribute − Composite attributes are made of more than one simple attribute. For example, a student's complete name may have first_name and last_name.
- 13. 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 Phone no in a department should not be saved directly in the database, instead it can be derived. For another example, age can be derived from data_of_birth.
- 14. Single-value attribute Single-value attributes contain single value. For example − Age of person is singal- valued attributes. Gender is also single-valued Attribute.
- 15. Multi-value attribute− Multi-value attributes may contain more than one values. For example, a person have Name, Address, Birthday, Age, hobbies etc.