The document discusses entity relationship modeling concepts including: - Entities represent real-world objects or concepts that can exist independently - Attributes describe entities with properties like simple or multi-valued attributes - Relationships exist between entities when one entity's attribute refers to another's attribute - Keys like primary keys and foreign keys are used to uniquely identify and relate entities - Cardinality defines relationship types as one-to-one, one-to-many, or many-to-many - Examples demonstrate applying these concepts to model systems like a university admissions system.

1. Entity Relationship model
Mehwish sabih

2. RECAP
• Basic Definition
• Collection of data files
• Complex definition
• A database is a structure that contains information about many kinds of
entitiesand about the relationshipsbetween those entities.

3. Entity/data object
• Entity is a real world item or a concept which can exist on its own. It
can be a physical object or it can be a concept. The entity is
represented by a rectangular shape.

4. Entity
• Entity can be a week entity which means that entity must be defined
by a foreign key relationship with another entity and it can’t be
defined independently or by its attributes only. Week entity is
represented as follows:

5. Attribute
• These are the properties that describe the entities.
• Attributes are further divided into following types:
• Simple attribute
• Single-valued attribute
• Multi-valued attribute
• Derived attribute

6. Relationship
• When attribute of one entity refers to the attribute of another entity
then there exists a relationship between these two entities.

7. Keys
• They are used to establish and identify relationships between tables.
• They uniquely identify any record or row of data inside a table.
• A Key can be a single attribute or a group of attributes, where the
combination may act as a key.
• Types:
• Primary key
• Candidate key
• Composite key
• Foreign key

8. Primary key
• Key that is unique for each record. E.g.
• Roll#
• Empid
• National Identity Card Number

9. Composite key
• A key that is composed of more than one attributes.
• Doctor(empid, name, specialization)
• Patient(pid, name, address, age)
• Appointment(pid, empid, Adate, status)

10. Candidate key

11. Foreign key

12. Cardinality
• Type of Relationships
• For a single record in one entity how many records in the adjacent
entity exist.
• 1:1
• 1:M
• M:M

13. Chen style of erd

14. Martin Style of
ERD

15. ERD-Example1 University Admissions System

16. Activity 1: Manufacturer
A manufacturing company produces products. The following product
information is stored: product name, product ID and quantity on hand. These
products are made up of many components. Each component can be
supplied by one or more suppliers. The following component information is
kept: component ID, name, description, suppliers who supply them, and
products in which they are used.
Assumptions
• A supplier can exist without providing components.
• A component does not have to be associated with a supplier.
• A component does not have to be associated with a product. Not all
components are used in products.
• A product cannot exist without components.

17. Activity 2: car dealership
The dealership sells both new and used cars, and it operates a service facility. Base your
design on the following business rules:
• A salesperson may sell many cars, but each car is sold by only one salesperson.
• A customer may buy many cars, but each car is bought by only one customer.
• A salesperson writes a single invoice for each car he or she sells.
• A customer gets an invoice for each car he or she buys.
• A customer may come in just to have his or her car serviced; that is, a customer need not
buy a car to be classified as a customer.
• When a customer takes one or more cars in for repair or service, one service ticket is
written for each car.
• The car dealership maintains a service history for each of the cars serviced. The
service records are referenced by the car’s serial number.
• A car brought in for service can be worked on by many mechanics, and each mechanic
may work on many cars.
• A car that is serviced may or may not need parts (e.g., adjusting a carburetor or cleaning
a fuel injector nozzle does not require providing new parts).

18. Activity 3- Automechanics
• Employee(empid, name, specialization, experience, rate)
• Customer(custid, name, address)
• Car(VPN, make, model, color)
• Service(servId, name, cost, hours_required)
• workOrder(woid, date, car)
• workOrder is created as an appointment for the car. There may be
many services provided by multiple employees for a particular
workorder called workOrderItems. For each workOrderItem employee
records wrapUpNotes.

22. Keep the schema and erd save for sql