Database Management Chapter 3

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Questions and Answers

What is the definition of a Relation in the relational model?

A table of values. (correct)

A list of attributes.

A collection of ordered pairs.

A graphical representation of data.

Who proposed the relational model of data and in which year?

Codd and Date, 1975

Ted Codd, 1970 (correct)

E.F. Codd, 1980

Alan Turing, 1972

In the context of a Relation schema, what does R (A1, A2,.....An) represent?

The table containing data.

A set of mathematical theorems.

The maximum number of tuples in a relation.

A relation defined over its attributes. (correct)

Which of the following best describes a tuple in a relation?

An ordered set of values representing a row. Signup and view all the answers

What is the main advantage of the relational approach to data management?

It is based on a formal mathematical foundation. Signup and view all the answers

What type of values does each column in a relation typically represent?

Values derived from an appropriate domain. Signup and view all the answers

In the CUSTOMER relation example, which of the following is NOT an attribute?

Total Purchase Signup and view all the answers

Which statement about rows in a relation is incorrect?

Rows can exist without being identified by a unique value. Signup and view all the answers

What are the columns in a table referred to as?

Attributes Signup and view all the answers

Which of the following is NOT a type of relational integrity constraint?

Functional constraints Signup and view all the answers

What defines a superkey in a relation?

A set of attributes that may have redundant values Signup and view all the answers

Which of the following describes a domain constraint?

It specifies that all attribute values must be atomic. Signup and view all the answers

How is a key defined within a relation?

As a superkey that is minimal and cannot have attributes removed Signup and view all the answers

Which of the following statements about tuples is correct?

The order of tuples does not matter. Signup and view all the answers

Which data types are typically associated with domains in database relations?

Standard numeric types, strings, and dates Signup and view all the answers

What does the term 'extension' refer to in a relational table context?

The collection of all tuples in a populated table Signup and view all the answers

What defines a superkey in a relation schema?

Any set of attributes that includes SSN. Signup and view all the answers

Which of the following statements regarding primary keys and null values is correct?

Primary key attributes cannot have null values in any tuple. Signup and view all the answers

Which of the following accurately describes referential integrity?

It specifies a relationship among tuples in two relations. Signup and view all the answers

In terms of referential integrity, which combination of values is allowed in the foreign key?

Existing primary key values or null. Signup and view all the answers

What must be ensured during update operations on relations?

Integrity constraints should not be violated. Signup and view all the answers

Which statement best illustrates a candidate key?

It can be a combination of multiple attributes that are unique. Signup and view all the answers

Which scenario would violate the rules of entity integrity?

Having a primary key as a null value. Signup and view all the answers

What happens if updates to a relation violate integrity constraints?

The update will be rejected, preventing data inconsistency. Signup and view all the answers

What is the outcome of deleting an EMPLOYEE tuple with SSN = ‘333445555’?

Referential integrity violations will occur. Signup and view all the answers

What is one possible action that can be taken in case of an integrity violation during an operation?

Trigger additional updates to correct the violation Signup and view all the answers

Which of the following updates to the EMPLOYEE tuple with SSN = ‘999887777’ would violate referential integrity?

Change the DNO to 7. Signup and view all the answers

What must be specified to perform an Update operation on a relation?

A condition on the attributes to select the tuples. Signup and view all the answers

Which type of constraint could be violated if a null value is given for a primary key during an insert operation?

Entity integrity Signup and view all the answers

Why is it unacceptable to update the SSN of an EMPLOYEE tuple with SSN = ‘999887777’?

It changes the primary key and violates referential integrity. Signup and view all the answers

What happens when an insert operation attempts to add a tuple with a primary key that already exists in the relation?

The insertion is rejected due to a key constraint violation Signup and view all the answers

What would be a consequence of deleting a tuple from the WORKS_ON relation?

Referential integrity violations will result. Signup and view all the answers

Which action is NOT typically allowed in response to an integrity violation during an insert operation?

Automatically fix the violation without user input Signup and view all the answers

What type of integrity violation can occur when deleting a tuple that is referenced by foreign keys in other tuples?

Referential integrity violation Signup and view all the answers

If an insert operation is performed with a foreign key value that does not reference an existing tuple, which constraint is violated?

Referential integrity Signup and view all the answers

What is a common result of a delete operation that violates referential integrity?

The deletion is rejected to preserve data integrity Signup and view all the answers

Which of the following is not a method to respond to integrity violations during operations?

Ignore the problem until later resolution Signup and view all the answers

Study Notes

Chapter 3: Relational Data Model and Relational Database Constraints

The relational model of data is based on the concept of a relation.
A relation is a mathematical concept based on the ideas of sets.
The strength of the relational approach to data management comes from the formal foundation provided by the theory of relations.
The relational model was first proposed by Ted Codd of IBM in 1970.
The paper "A Relational Model for Large Shared Data Banks" was published in Communications of the ACM, June 1970.
This paper revolutionized database management and earned Ted Codd the ACM Turing Award.

Relational Model Concepts

A relation can be thought of as a table of values.
A relation can be thought of as a set of rows.
A relation can be thought of as a set of columns.
Each row in a relation represents a fact corresponding to a real-world entity or relationship.
Each row has a value (or set of values) that uniquely identifies that row.
Rows in a table are sometimes identified by row-ids or sequential numbers.
Columns are typically identified by their column name, column header, or attribute name.
A relation schema is defined as R(A1, A2, ..., An), where attributes are represented as A1, A2, etc., up to An.
Example: CUSTOMER (Cust-id, Cust-name, Address, Phone#)
A tuple is an ordered set of values, derived from an appropriate domain.
Each row in the CUSTOMER table is a tuple.
Example tuple: <632895, "John Smith," "101 Main St., Atlanta, GA 30332," "(404) 894-2000">

Definition Summary

Informal Terms: Table, Column, Row, Values in a column, Table Definition, Populated Table
Formal Terms: Relation, Attribute/Domain, Tuple, Domain, Schema of a Relation, Extension

Example

Relation Name: STUDENT
Attributes: Name, SSN, Home_phone, Address, Office_phone, Age, GPA
Example tuples from the STUDENT relation are given.

Note

Ordering of Tuples in a relation
Ordering of Values within a Tuple
Values and NULLs in the Tuples

Relational Integrity Constraints

Constraints are conditions that must hold on all valid relation instances.
There are four types of constraints:
- Domain constraints
- Key constraints
- Entity integrity constraints
- Referential integrity constraints

Domain Constraints

Domain constraints specify that the value of each attribute A must be an atomic value from the domain dom(A).
Data types associated with domains typically include standard numeric data types (integers, real numbers), characters, fixed-length strings, variable-length strings, date, time, timestamp, and money data types.

Key Constraints

A relation is defined as a set of tuples. All elements of a set are distinct.
No two tuples can have the same combination of values for all their attributes.
A superkey of R is a set of attributes SK of R such that no two tuples in any valid relation instance r(R) will have the same value for SK.
Every relation has at least one default superkey. A superkey can have redundant attributes.
A key is a "minimal" superkey; removing any attribute from the key results in a set of attributes that is not a superkey.
For example, in the STUDENT relation, {SSN} is a key; it is a minimal superkey.
{SSN, Name, Age} is a superkey (but not a key).

Entity Integrity

The primary key attributes (PK) of each relation schema R cannot have null values in any tuple of r(R).
This is because primary key values are used to identify individual tuples. (t[PK] ≠ null for any tuple t in r(R))
Other attributes might have constraints preventing null values even if not part of the primary key.

Referential Integrity

A constraint involving two relations.
Used to specify a relationship among tuples in two relations (referencing and referenced).
Tuples in referencing relation R₁ have attributes (FK) that reference the primary key attributes (PK) of the referenced relation R₂.
A tuple t₁ in R₁ references a tuple t₂ in R₂ if t₁[FK] = t₂[PK].
A referential integrity constraint can be displayed as a directed arc from R₁.FK to R₂.

Statement of Referential Integrity Constraint

The value in the foreign key column (or columns) FK of the referencing relation R₁ can be either:

a value of an existing primary key value of the corresponding primary key PK in the referenced relation R₂, or
a null. In case (2), the FK in R₁ should not be part of its own primary key.

Update Operations on Relations

INSERT, DELETE, MODIFY tuples.
Integrity constraints should not be violated by update operations.
Several update operations may need to be grouped together.
Updates may automatically cause other updates to maintain integrity constraints.

Actions in Case of Integrity Violation

Cancel the operation causing the violation (REJECT option).
Perform the operation but inform the user (violation).
Trigger additional updates (CASCADE option, SET NULL option).
Execute a user-specified error-correction routine.

Insert Operation

Provides a list of attribute values for a new tuple t to insert into a relation R.
Insert operation can violate domain constraints, key constraints, entity integrity, or referential integrity constraints.

Delete Operation

Can only violate referential integrity (if referenced by foreign keys in other tuples).
A condition on attributes selects tuples to be deleted.

Update Operation

The update operation changes values of one or more attributes in a tuple (or tuples) within a relation.

Update Operations Examples

Examples of acceptable and unacceptable update operations are given.

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Description

This quiz covers the relational data model and its constraints as presented in Chapter 3. Explore the mathematical foundations of relations and discover the groundbreaking work of Ted Codd in revolutionizing database management. Test your understanding of these fundamental concepts in relational databases.