Bdate Ename Minit Name EMPLOYEE Lname Sex Address Salary N WORKS FOR Start_date MANAGES Supervisor Supervisees SUPERVISION M WORKS ON Hours Name Location Number Number of employees DEPARTMENT CONTROLS PROJECT Number Name Location 1900 Relationship Bdate N DEPENDENTS OF DEFENDENT
A Dia file has been created for you to extend and can be found on Company.dia represents a completed ER schema which, models some of the information implemented in the system, as a starting point for this exercise.
Understanding the ER schema for the Company database.
To demonstrate that you understand the information represented by the schema, explain using EMPLOYEE, DEPARTMENT, PROJECT and DEPENDENT as examples:
- attributes, entities and relationships
- cardinality & participation constraints on relationships
You should explain questions a and b using the schema you have been given to more easily explain your answers.
Creating and Extending Entity Relationship (EER) Diagrams.
To demonstrate you can create entity relationship diagrams extend the ER as described in Company.dia by modelling new requirements as follows:
- Create subclasses to extend Employee. The employee type may be distinguished further based on the job type (SECRETARY, ENGINEER, MANAGER, and TECHNICIAN) and based on the method of pay (SALARIED_EMPLOYEE, HOURLY_EMPLOYEE)
SECRETARY entity type has the specific attribute Typing_speed, whereas the ENGINEER entity type has the specific attribute Eng_type, but SECRETARY and ENGINEER share their other inherited attributes from the EMPLOYEE entity type.
SALARIED_EMPLOYEE entity type has the specific attribute Salary, whereas the HOURLY_EMPLOYEES entity type has the specific attribute Pay_scale.
- Now explain the superclass and subclasses that you have just created.
- Explain the disjointness (overlap/disjoint) and completeness (partial/total) constraints you have made while creating the specialization in question a.
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