---
title: "RA: employees on project DBMS"
subject: "Database Management System"
chapter: 3
key: "semester_6/database_management_system:ra-emp-project-dbms"
source: https://www.bctengineer.com/q/semester_6/database_management_system/ra-emp-project-dbms
site: BCT Engineering
---

# RA: employees on project DBMS

Database Management System · Chapter 3: Relational Languages & Relational Model

- Asked in: year not given
- Video: [Relational Algebra Expressions with Employee, Department & Project Tables | DBMS Module 2 BCS403 VTU](https://www.youtube.com/watch?v=99trDPSh7XY) — Express VTU 4 All
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/database_management_system/ra-emp-project-dbms
- Whole chapter: https://www.bctengineer.com/md/semester_6/database_management_system/chapter-3

## Question

Consider the relational schema:
employee (e_no, name, address)
project (p_no, p_name)
work (e_no, p_no)
part (part_no, part_name, qty, size)
use (e_no, p_no, part_no, number)
Print names of employees working on project named "DBMS". (Write a relational algebra expression.)

## Short answer

Natural join employee, work, project; select where p_name = 'DBMS'; project name: π name (σ p_name='DBMS' (employee ⋈ work ⋈ project)).

## Answer

Relational algebra symbols used: σ select, π project, ⋈ natural join, ∪ union, ∩ intersection, − difference, ρ rename, 𝒢 aggregate.

#### Relational algebra expression
```text
π name ( σ p_name = "DBMS" ( employee ⋈ work ⋈ project ) )
```

#### Explanation
1. employee ⋈ work joins on the common attribute e_no, so each employee is paired with the projects he or she works on.
2. The result ⋈ project joins on p_no and brings in the project name.
3. σ p_name = "DBMS" keeps only the tuples of the DBMS project.
4. π name outputs only the employee names (duplicates are removed automatically in relational algebra).

#### Equivalent SQL (checked on sample data)
```sql
SELECT DISTINCT e.name
FROM employee e JOIN work w ON e.e_no = w.e_no
                JOIN project p ON p.p_no = w.p_no
WHERE p.p_name = 'DBMS';
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why must employee, work and project all be joined?
   A. Only employee is needed because it has the name
   B. employee has the name, project has p_name, and work links them via e_no and p_no
   C. Join is needed only to remove duplicates
   D. work and project share e_no
   Answer: B. work connects employee to project; the project name is only in project. (Key point: Join chain)

2. Which operator keeps only the DBMS tuples, and which outputs names?
   A. pi p_name = DBMS keeps them; sigma name outputs names
   B. Both are done by natural join
   C. Union removes non-DBMS tuples
   D. sigma p_name = DBMS keeps them; pi name outputs names
   Answer: D. Selection filters rows; projection chooses columns. (Key point: Selection then projection)

3. What happens to duplicate names in the result?
   A. They are kept
   B. They are removed automatically because relational algebra works on sets
   C. An error occurs
   D. They need the DISTINCT operator in algebra
   Answer: B. Relations are sets; SQL needs DISTINCT but algebra does not. (Key point: Duplicates)

## Close variants set in other exams

- [RA: employees on no project](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-emp-no-project) — Database Management System, chapter 3

## Related in Database Management System

- [RA: employee-projects with no part used](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-emp-project-no-part) — Database Management System, chapter 3
- [RA: employees in both DBMS and MIS](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-emp-both-dbms-mis) — Database Management System, chapter 3
- [RA: parts used in DBMS and MIS](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-parts-both-dbms-mis) — Database Management System, chapter 3
- [RA: projects where all used bolts size 6](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-projects-all-used-bolts) — Database Management System, chapter 3
- [RA: computer dept employees and supervisors](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-computer-emp-supervisor) — Database Management System, chapter 3
- [RA: employees on Network over 15 hours](https://www.bctengineer.com/question.md?key=semester_6%2Fdatabase_management_system%3Ara-network-project-15-hours) — Database Management System, chapter 3