For the above given database STUDENT-PROJECT, answer the following: Student Project Database Table: PROJECT | ProjectNo | PName | SubmissionDate | |---|---|---| | 101 | Airline Database | 12/01/2018 | | 102 | Library Database | 12/01/2018 | | 103 | Employee Database | 15/01/2018 | | 104 | Student Database | 12/01/2018 | | 105 | Inventory Database | 15/01/2018 | | 106 | Railway Database | 15/01/2018 | Table: PROJECT ASSIGNED | Registration_ID | ProjectNo | |---|---| | IP-101-15 | 101 | | IP-104-15 | 103 | | CS-103-14 | 102 | | CS-101-14 | 105 | | CS-101-10 | 104 | Table: STUDENT | Roll No | Name | Class | Section | Registration_ID | |---|---|---|---|---| | 11 | Mohan | XI | 1 | IP-101-15 | | 12 | Sohan | XI | 2 | IP-104-15 | | 21 | John | XII | 1 | CS-103-14 | | 22 | Meena | XII | 2 | CS-101-14 | | 23 | Juhi | XII | 2 | CS-101-10 | (a) Name primary key of each table. (b) Find foreign key(s) in table PROJECT-ASSIGNED. (c) Is there any alternate key in table STUDENT? Give justification for your answer. (d) Can a user assign duplicate value to the field RollNo of STUDENT table? Jusify.

> [!TLDR] > This solution identifies primary keys, foreign keys, and alternate keys in the given database schema, and explains the uniqueness constraint on primary keys. Understanding the structure of a database, specifically its keys, is fundamental to designing efficient and reliable systems. Keys define relationships between tables and enforce data integrity, ensuring that data is consistent and accurate. Let's break down the concepts for the `STUDENT-PROJECT` database. ### **(a) Name primary key of each table.** A primary key is a column or a set of columns that uniquely identifies each row in a table. It must contain unique values for each row and cannot contain NULL values. Its purpose is to ensure entity integrity, meaning every entity (row) in the table is uniquely identifiable. * **Table: PROJECT** The `ProjectNo` column contains unique values (101, 102, 103, 104, 105, 106) for each project and does not appear to have any NULL values. It serves as a clear identifier for each project. > [!IMPORTANT] > The primary key for the `PROJECT` table is **ProjectNo**. * **Table: PROJECT ASSIGNED** This table links students to projects. Neither `Registration_ID` nor `ProjectNo` alone can uniquely identify a row, as a student might be assigned multiple projects (though not shown in this sample, it's a possibility in a real system), or a project might be assigned to multiple students. However, the combination of `Registration_ID` and `ProjectNo` uniquely identifies each assignment record. For example, `(IP-101-15, 101)` is a unique pair. > [!IMPORTANT] > The primary key for the `PROJECT ASSIGNED` table is the composite key **(Registration_ID, ProjectNo)**. * **Table: STUDENT** The `Roll No` column contains unique values (11, 12, 21, 22, 23) for each student and does not contain NULL values. It is the most natural and common identifier for students in an academic context. > [!IMPORTANT] > The primary key for the `STUDENT` ta

For the above given database STUDENT-PROJECT, answer the following: Student Project Database Table: PROJECT |

Exercises · Q12

For the above given database STUDENT-PROJECT, answer the following:

Student Project Database

Table: PROJECT

ProjectNo	PName	SubmissionDate
101	Airline Database	12/01/2018
102	Library Database	12/01/2018
103	Employee Database	15/01/2018
104	Student Database	12/01/2018
105	Inventory Database	15/01/2018
106	Railway Database	15/01/2018

Table: PROJECT ASSIGNED

Registration_ID	ProjectNo
IP-101-15	101
IP-104-15	103
CS-103-14	102
CS-101-14	105
CS-101-10	104

Table: STUDENT

Roll No	Name	Class	Section	Registration_ID
11	Mohan	XI	1	IP-101-15
12	Sohan	XI	2	IP-104-15
21	John	XII	1	CS-103-14
22	Meena	XII	2	CS-101-14
23	Juhi	XII	2	CS-101-10

Name primary key of each table.
Find foreign key(s) in table PROJECT-ASSIGNED.
Is there any alternate key in table STUDENT? Give justification for your answer.
Can a user assign duplicate value to the field RollNo of STUDENT table? Jusify.

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Concept understanding — Database Schema

Database Schema: The Blueprint of a Database

Imagine you are organising a large library. You don't just pile books randomly. First, you decide: What information will we keep about each book? Title, author, ISBN, shelf number. Then you decide: How are these pieces of information related? A book has one shelf, but a shelf holds many books. You also decide rules: Every book must have an ISBN; no two books can share the same ISBN.

That plan — the structure you design before you put a single book on the shelf — is the schema.

The Precise Meaning

A database schema is the formal, logical description of how data is organised in a database. It defines:

What tables exist (like "Books", "Members", "Loans")
What columns each table has (e.g., BookID, Title, Author, YearPublished)
What type of data each column holds (text, number, date, etc.)
What rules or constraints apply (e.g., "Every loan must refer to an existing member")
How tables relate to one another (e.g., "A member can borrow many books, but each loan record belongs to one member")

Think of the schema as the skeleton of the database. The actual data — the rows you fill in later — is the flesh and blood. The schema stays mostly unchanged; the data changes constantly.

Note

A common confusion: people say "the database" when they mean the data inside it. But the schema is the structure, not the data. Two databases can have the same schema but completely different data — like two schools using the same student record form but with different students' names.

Why the Schema Matters

Without a schema, data becomes a mess. You might store a customer's phone number in the "Name" column, or lose track of which orders belong to which customer. The schema prevents this by enforcing consistency and integrity.

Consider a bank. The schema says: "Every transaction must have an amount, a date, and a valid account number." If someone tries to enter a transaction without an account number, the database refuses — because the schema says so. This is not a software bug; it is a deliberate design choice built into the structure.

Key Components of a Schema

Tables – The main containers. Each table represents one kind of thing (Students, Products, Invoices).
Columns (Fields) – The attributes or properties of that thing (StudentName, DateOfBirth, Email).
Data Types – What kind of value each column holds (text, whole number, decimal, date).
Constraints – Rules that data must obey:
- Primary Key – A unique identifier for each row (like a roll number). No two rows can share it.
- Foreign Key – A column that links to another table's primary key, creating a relationship.
- Not Null – A column that must always have a value.
- Unique – A column where every value must be different.
Relationships – How tables connect: one-to-one, one-to-many, many-to-many. …

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Here are the answers to the given questions about the STUDENT-PROJECT database schema:

(a) Name primary key of each table.

A primary key is a column or a set of columns that uniquely identifies each row in a table. It must contain unique values and cannot be NULL.

PROJECT table: The primary key is ProjectNo. Each project has a unique ProjectNo.
PROJECT ASSIGNED table: The primary key is a composite key consisting of (Registration_ID, ProjectNo). This combination uniquely identifies each instance of a student being assigned a specific project.
STUDENT table: The primary key is Roll No. Each student has a unique Roll No.

(b) Find foreign key(s) in table PROJECT ASSIGNED.

A foreign key is a column or a set of columns in one table that refers to the primary key in another table. It establishes a link between two tables.

In the PROJECT ASSIGNED table:

Registration_ID is a foreign key that references the Registration_ID column in the STUDENT table.
ProjectNo is a foreign key that references the ProjectNo column in the PROJECT table.

(c) Is there any alternate key in table STUDENT? Give justification for your answer.

Yes, there is an alternate key in the STUDENT table.

An alternate key is a candidate key that is not chosen as the primary key. A candidate key is any column or set of columns that can uniquely identify each row in a table.

In the STUDENT table:

Roll No is the primary key.
Registration_ID also contains unique values for each student (e.g., IP-101-15, IP-104-15, CS-103-14, etc.). Therefore, Registration_ID is also a candidate key. Since Roll No has been chosen as the primary key, Registration_ID serves as an alternate key.

(d) Can a user assign duplicate value to the field RollNo of STUDENT table? Justify.

No, a user cannot assign a duplicate value to the RollNo field of the STUDENT table. …

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This solution identifies primary keys, foreign keys, and alternate keys in the given database schema, and explains the uniqueness constraint on primary keys.

Understanding the structure of a database, specifically its keys, is fundamental to designing efficient and reliable systems. Keys define relationships between tables and enforce data integrity, ensuring that data is consistent and accurate. Let's break down the concepts for the STUDENT-PROJECT database.

(a) Name primary key of each table.

A primary key is a column or a set of columns that uniquely identifies each row in a table. It must contain unique values for each row and cannot contain NULL values. Its purpose is to ensure entity integrity, meaning every entity (row) in the table is uniquely identifiable.

Table: PROJECT

The ProjectNo column contains unique values (101, 102, 103, 104, 105, 106) for each project and does not appear to have any NULL values. It serves as a clear identifier for each project.

Important

The primary key for the PROJECT table is ProjectNo.
Table: PROJECT ASSIGNED

This table links students to projects. Neither Registration_ID nor ProjectNo alone can uniquely identify a row, as a student might be assigned multiple projects (though not shown in this sample, it's a possibility in a real system), or a project might be assigned to multiple students. However, the combination of Registration_ID and ProjectNo uniquely identifies each assignment record. For example, (IP-101-15, 101) is a unique pair.

Important

The primary key for the PROJECT ASSIGNED table is the composite key (Registration_ID, ProjectNo).
Table: STUDENT

The Roll No column contains unique values (11, 12, 21, 22, 23) for each student and does not contain NULL values. It is the most natural and common identifier for students in an academic context.

Important

The primary key for the STUDENT table is Roll No.

(b) Find foreign key(s) in table PROJECT ASSIGNED.

A foreign key is a column or a set of columns in one table that refers to the primary key in another table. It establishes a link between two tables, enforcing referential integrity. This means that values in the foreign key column(s) must either match a value in the primary key of the referenced table or be NULL (if allowed).

In the PROJECT ASSIGNED table:

The Registration_ID column contains values like 'IP-101-15', 'IP-104-15', 'CS-103-14', etc. These values correspond to the Registration_ID column in the STUDENT table, which is an alternate key (and a candidate for a primary key) in that table. This establishes a link between an assignment and a specific student.
The ProjectNo column contains values like 101, 103, 102, etc. These values correspond to the ProjectNo column in the PROJECT table, which is its primary key. This establishes a link between an assignment and a specific project.

Therefore, PROJECT ASSIGNED has two foreign keys.

Important

The foreign keys in the PROJECT ASSIGNED table are Registration_ID (referencing STUDENT table) and ProjectNo (referencing PROJECT table).

(c) Is there any alternate key in table STUDENT? Give justification for your answer.

An alternate key is any candidate key that is not chosen as the primary key for a table. A candidate key is a minimal set of attributes that can uniquely identify a tuple (row) in a table. It must be unique and non-nullable.

In the STUDENT table:

We identified Roll No as the primary key because it uniquely identifies each student.
Consider the Registration_ID column. Its values ('IP-101-15', 'IP-104-15', 'CS-103-14', 'CS-101-14', 'CS-101-10') are unique for each student in the table and do not contain NULL values. This means Registration_ID also has the properties of a candidate key.

Since Registration_ID is a candidate key but Roll No was chosen as the primary key, Registration_ID qualifies as an alternate key.

Important

Yes, Registration_ID is an alternate key in the STUDENT table.

…

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(a) Name primary key of each table.

(b) Find foreign key(s) in table PROJECT ASSIGNED.

(c) Is there any alternate key in table STUDENT? Give justification for your answer.

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