Entity relationship diagram (erd)
- 2. GROUP MEMBERS MD. Shahariar Alam (162-15-8113) Avijit Roy (162-15-7898) MD. Monir Hossain (162-15-8033) MD. Muin Mahmud (162-15-7983) MD. Hasanuzzaman (162-15-8025) Amiya Adhikary (162-15-7980)
- 3. WHAT IS AN ERD & WHY IT IS USED? Database systems are often modeled using an Entity Relationship Diagram (ERD) as the "blueprint" from which the actual data is stored. The ERD is used to communicate the logical structure of the database to users.
- 4. Entity: An entity can be a real-world object, either animate or inanimate, that can be easily identifiable. Example: Person Place Object Entity Set: An entity set is a collection of similar types of entities. An entity set may contain entities with attribute sharing similar values.
- 5. ATTRIBUTES Entities are represented by means of their properties, called attributes. All attributes have values. Example : Student :- Name, Class, Age Types ofAttributes: Simple attribute: Simple attributes are atomic values, which cannot be divided further. Example:The entities like age, marital status cannot be subdivided and are simple attributes. Composite attribute: A composite attribute is one that is composed of smaller parts. Example: Name, Date of Birth.
- 6. Derived attribute: A derived attribute is an attribute whose value is calculated (derived) from other attributes. Example: Age, it can be calculated from date of birth. Single-value attribute: Single-value attributes contain single value. Example: Gender, Date of Birth. Multi-value attribute: Multi-value attributes may contain more than one values. Example: Phone number, Email.
- 7. RELATIONSHIP Associations between instances of one or more entity types that is of Interest.
- 8. Degree of Relationship Binary Relationship: between the instances of two entity types. Teacher SubjectTeaches
- 9. Ternary Relationship:Among the instances of three entity types. Teacher StudentTeaches Subject
- 10. CARDINALITY Cardinality defines the number of entities in one entity set, which can be associated with the number of entities of other set via relationship set. One to one One to many Many to one Many to many
- 11. KEY CONSTRAINTS Super Key Candidate Key Primary Key Foreign Key Attribute Primary Key Candidate KeySuper Key
- 12. GENERAL STEPS TO CREATE AN ERD Identify the entities Identify the relation between entities Identify the Cardinality constraint Identify the entity's attributes Draw the ERD
- 13. A SIMPLE EXAMPLE A company has several departments. Each department has a supervisor and at least one employee. Every supervisor has only one department under him. Employees must be assigned to at least one, but possibly more departments.At least one employee is assigned to a project, but an employee may be on vacation and not assigned to any projects.The important data fields are the names of the departments, projects, supervisors and employees. Supervisors and Employees also have ID, Email, Phone and a unique project number.
- 15. RELATIONAL SCHEMA Department(Department_Name) Supervisor(S_ID, Name, Email, Phone, Department_Name) Employee(E_ID, Name, Email, Phone, Project_Number) Project(Project_Number, Project_Name)