Database Design and ER Diagrams
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Questions and Answers

What should be done with a multi-valued attribute in a database?

It should be turned into a new entity or table of its own.

What type of relationship is established between the new table created for a multi-valued attribute and the parent entity?

A 1:N relationship is established.

How should the primary key from the parent entity be represented in the new table?

It should be added as a foreign key in the new table.

In a 1:1 relationship, what key can be added to the Persons table to indicate a relationship to the Wife table?

<p>The wifeid can be included as a foreign key in the Persons table.</p> Signup and view all the answers

What modification is needed for the Persons table if a person is not married?

<p>The wifeid field should not be included in the Persons table.</p> Signup and view all the answers

What is aggregation in the context of entity-relationship diagrams?

<p>Aggregation is an abstraction that treats relationships as higher-level entities.</p> Signup and view all the answers

How should primary key attributes be named in a table?

<p>Primary key attributes should conventionally start with 'TablenameID'.</p> Signup and view all the answers

What happens to an entity type when transformed from an ER diagram into a relational schema?

<p>An entity type becomes a table, with each attribute turning into a column.</p> Signup and view all the answers

What is a multi-valued attribute represented by in an ER diagram?

<p>A multi-valued attribute is represented by a double-line oval.</p> Signup and view all the answers

What is the format for expressing an initial relational schema?

<p>The format is 'TableName(Attribute1, Attribute2, ...)' with attributes listed in parentheses.</p> Signup and view all the answers

Why should special characters and DBMS reserved words be avoided in table names?

<p>Special characters and reserved words can lead to errors and confusion in database management.</p> Signup and view all the answers

What is the recommended approach for primary keys that are composite?

<p>Composite primary keys can be used but must never be null.</p> Signup and view all the answers

How are both entities and relationship sets treated when using aggregation?

<p>Both are treated as a higher-level entity set for combined representation.</p> Signup and view all the answers

What does SQL stand for and what is its primary purpose?

<p>SQL stands for Structured Query Language, and its primary purpose is to access and manipulate databases.</p> Signup and view all the answers

Describe the relational model and its fundamental building blocks.

<p>The relational model stores data in tables, which are the fundamental building blocks of the database.</p> Signup and view all the answers

List two operations that can be performed using SQL.

<p>Two operations that can be performed using SQL are retrieving data from a database and updating existing records.</p> Signup and view all the answers

What is the function of Data Definition Language (DDL) in SQL?

<p>DDL statements are used to define the database structure or schema, including creating and altering database objects.</p> Signup and view all the answers

Explain the difference between the DELETE and TRUNCATE commands in SQL.

<p>The DELETE command removes records from a table while preserving the space for those records, whereas TRUNCATE removes all records and the space allocated for them.</p> Signup and view all the answers

What are some of the key tasks you can accomplish with SQL besides querying data?

<p>Besides querying data, SQL allows for creating new databases, tables, stored procedures, and views.</p> Signup and view all the answers

What is the purpose of Data Control Language (DCL) in SQL?

<p>DCL is used to control access to data in the database, including setting permissions on tables, procedures, and views.</p> Signup and view all the answers

Identify and explain one command used in Data Manipulation Language (DML).

<p>One command in DML is SELECT, which retrieves data from a database based on specified criteria.</p> Signup and view all the answers

What is the purpose of linking the employee and department tables in a database?

<p>To associate each employee with their respective department, allowing for proper organization of data.</p> Signup and view all the answers

Define alternate key in the context of database relations.

<p>An alternate key is a candidate key that is not selected as the primary key but can still uniquely identify records in a table.</p> Signup and view all the answers

How is a composite key different from a regular primary key?

<p>A composite key consists of two or more attributes that together uniquely identify a record, while a regular primary key consists of a single attribute.</p> Signup and view all the answers

Can a table have more than one alternate key? Explain.

<p>Yes, a table can have multiple alternate keys if it has more than one candidate key aside from the primary key.</p> Signup and view all the answers

Give an example of how a composite key might be used in an employee relation.

<p>In an employee relation, a composite key might include Emp_ID, Emp_role, and Proj_ID to uniquely identify each employee's assignment in a project.</p> Signup and view all the answers

What role does the foreign key play in database tables?

<p>A foreign key establishes a relationship between two tables, referencing the primary key of another table to ensure data integrity.</p> Signup and view all the answers

Why might a company choose to use alternate keys in their database design?

<p>Companies use alternate keys to provide additional unique identifiers for records, improving data retrieval and ensuring unique data entry.</p> Signup and view all the answers

In a scenario where an employee has multiple roles, why is a composite key necessary?

<p>A composite key is necessary to uniquely identify each combination of employee roles and projects, preventing data duplication.</p> Signup and view all the answers

What is the purpose of the GRANT command in a database?

<p>The GRANT command is used to give users access privileges to the database.</p> Signup and view all the answers

How does the REVOKE command function in database management?

<p>The REVOKE command withdraws access privileges that were previously granted with the GRANT command.</p> Signup and view all the answers

What does the COMMIT command do in Transaction Control Language (TCL)?

<p>The COMMIT command saves all work done in a transaction.</p> Signup and view all the answers

What is a SAVEPOINT and its function in a transaction?

<p>A SAVEPOINT identifies a point within a transaction to which you can later roll back.</p> Signup and view all the answers

What is the difference between DML and DDL in terms of transaction control?

<p>DML statements are not auto-committed and can be rolled back, while DDL statements are auto-committed.</p> Signup and view all the answers

What are the key components of the basic SQL SELECT statement syntax?

<p>The basic SQL SELECT statement syntax includes SELECT column list, FROM table name, and optional WHERE, GROUP BY, HAVING, and ORDER BY clauses.</p> Signup and view all the answers

Provide an example of a SELECT statement that retrieves specific columns with an alias.

<p>An example is: <code>SELECT Sname, Sno AS Rollno FROM Student</code>.</p> Signup and view all the answers

How can mathematical operations be included in a SELECT statement?

<p>Mathematical operations can be performed directly in the SELECT statement, such as <code>SELECT Sno, Sname, Eng + Maths AS Total FROM Student</code>.</p> Signup and view all the answers

What distinguishes a trivial functional dependency from a nontrivial one?

<p>A trivial functional dependency occurs when the right-hand side is a subset of the left-hand side, while a nontrivial dependency has a right-hand side that is not a subset of the left-hand side.</p> Signup and view all the answers

Provide an example of a trivial functional dependency.

<p>{S#, P#} → S# is a trivial functional dependency.</p> Signup and view all the answers

Explain the concept of closure in the context of functional dependencies.

<p>Closure refers to the set of all attributes that can be functionally determined by a given set of attributes.</p> Signup and view all the answers

What is the significance of normalization in database management?

<p>Normalization helps to minimize data redundancy and eliminate anomalies such as insertion, update, and deletion anomalies.</p> Signup and view all the answers

Define augmentation in the context of functional dependencies.

<p>Augmentation states that if A → B holds, then adding attributes to both sides results in AC → BC.</p> Signup and view all the answers

List one advantage of normalizing a database.

<p>One advantage is the reduction of data redundancy, which increases data integrity and effectiveness.</p> Signup and view all the answers

What does the decomposition rule in functional dependencies entail?

<p>Decomposition allows a single functional dependency A → BC to be broken down into A → B and A → C.</p> Signup and view all the answers

Summarize the principle of transitivity in functional dependencies.

<p>Transitivity states that if A → B and B → C, then A → C holds true.</p> Signup and view all the answers

Flashcards

Handling Multi-Valued Attributes

Converting a multi-valued attribute into a separate entity (table) and creating a 1:N relationship between the new entity and the original one.

Creating a New Table for Multi-Valued Attribute

A new table is created to store the values of the multi-valued attribute, like storing phone numbers in a 'Phones' table.

Foreign Key

A field (column) in one table that refers to the primary key of another table, creating a link between them.

1:N Relationship

A relationship where one record in one table can have many records in another table. For instance, one person can have multiple phone numbers.

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1:1 Relationship

A relationship where one record in one table is related to exactly one record in another table. For instance, a person having one spouse can have that information in a table linking to another table, each person one to one.

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SQL

Structured Query Language; a standard language for accessing and manipulating relational databases.

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Relational Database

A database that organizes data into tables with relationships between them.

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DDL

Data Definition Language; used to define the structure of a database.

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DML

Data Manipulation Language; used to manipulate data within the database.

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DCL

Data Control Language; used to control access to data and privileges.

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CREATE

A DDL command to create database objects like tables.

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SELECT

A DML command to retrieve data from a table.

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Table

A fundamental structure in a relational database to store data in rows and columns.

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Aggregation in E-R diagrams

A technique to treat relationships as higher-level entities in an Entity-Relationship diagram.

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Relationship sets

In an E-R diagram, sets of relationships between entities.

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Primary Key

A column (attribute) in a table uniquely identifying each row/record.

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Table creation from E-R diagram

Generating tables based on entities and relationships in an E-R diagram to represent data.

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Multi-Valued Attribute

Attributes that can hold multiple values for a single entity.

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Entity Type

A distinct category about data which is represented in a database.

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Attribute

A characteristic or property of an entity. In a table it is a column.

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Relational Schema

Describes the structure of a relational database as a collection of tables and their attributes.

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Candidate Key

Attribute(s) that uniquely identify every row in a table, potentially acting as the primary key.

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Alternate Key

A candidate key that is not chosen as the primary key in a table.

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Composite Key

A primary key that is formed by combining multiple attributes.

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What is the purpose of a foreign key?

A foreign key helps link two tables together, allowing information to be accessed and managed across related data.

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Why use a composite key?

A composite key is needed when a single attribute cannot uniquely identify a row in a table.

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Example of Alternate Key

In a table with 'Employee_Id' and 'Social_Security_Number' as candidate keys, if 'Employee_Id' is the primary key then 'Social_Security_Number' becomes the alternate key.

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Trivial Dependency

A functional dependency where the right-hand side attributes are already included in the left-hand side attributes. For example: {S#, P#} → S#

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Nontrivial Dependency

A functional dependency where the right-hand side attributes are not fully included in the left-hand side attributes. For example: {S#, P#} → QTY

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What is a functional dependency?

A relationship between two sets of attributes where the values of one set determine the values of the other set. This means knowing the values of the first set lets you know the values in the second set.

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Closure of Dependencies

A set of rules that help analyze and derive new functional dependencies from existing ones.

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Reflexivity

Rule stating: If B is a subset of A, then A → B. This means if a set of attributes already contains another set, then the larger set determines the smaller set.

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Augmentation

Rule stating: If A → B, then AC → BC. This means adding the same attribute(s) to both sides of a dependency does not change the dependency.

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Transitivity

Rule stating: If A → B and B → C, then A → C. This means if A determines B and B determines C, then A also determines C.

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Normalization

A process of organizing a database to minimize redundancy and improve data integrity. It involves analyzing the structure of tables and their relationships to eliminate anomalies (data inconsistencies).

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GRANT

Gives a user access privileges to a database. It allows users to perform specific actions, like reading, writing, or modifying data.

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REVOKE

Withdraws the access privileges previously given with the GRANT command. It removes a user's ability to perform specific actions on the database.

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COMMIT

Saves the changes made within a transaction. Once committed, the changes are permanently applied to the database.

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SAVEPOINT

Marks a specific point within a transaction. Used to roll back the transaction to that point if needed.

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ROLLBACK

Undoes the changes made in a transaction, restoring the database to the state it was in before the transaction started. It can also be used to undo changes since the last COMMIT.

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Study Notes

Unit 1: Introduction to Database

  • Introduction to Databases, DBMS, and applications of DBMS
  • Purpose of DBMS, Data Independence
  • Types of Database System Architecture (1-tier, 2-tier, 3-tier)
  • Database System levels (External, Conceptual, Internal), Mappings
  • Database, Users, and DBA
  • Introduction to types of Data Models
  • Hierarchical data model, Network Model, Relational Model, and E-R Data Model
  • Facts that can be recorded or stored (e.g., Person Name, Age, Gender, Weight)
  • Information - Processed, organized, structured, or presented data in a given context to be useful
  • Database - A collection of logically related data (e.g., Books database in a library, Student database in a university)
  • DBMS (Database Management System) - A collection of inter-related data and programs that manipulate the data (examples: MS SQL Server, Oracle, MySQL, SQLite, MongoDB)
  • Metadata - Data about data (e.g., table name, column name, data type, authorized user, and user access privileges for a table)
  • Data dictionary, Data warehouse, Field, Record

Applications of DBMS

  • Railway Reservation System - Keeps track of ticket bookings, train schedules, and status updates
  • Library Management System - Tracks books, manages borrowing, and makes information accessible
  • Banking Systems - Processes transactions, manages accounts, and provides financial services
  • Universities and Colleges- Manages student enrolment, registration, grades, courses
  • Credit card transactions - Securely stores and manages credit card transactions
  • Social Media Sites - Stores user data, posts, and interactions
  • Finance - Manages finances, information, and statements
  • Military Systems - Securely stores and manages data about personnel, equipment, and transactions
  • Online Shopping - Records product details, orders, and payments
  • Human Resource Management- Stores and manages information about employees, such as salary, tax, and work details
  • Manufacturing - Stores and manages information about products and their production
  • Airline Reservation Systems - Tracks flight schedules, bookings, and other related data

Data Independence

  • Data independency is the ability to modify a schema definition in one level without affecting the schema definition in the next higher level.
  • Types of Data Independence:
    • Physical data independence
    • Logical data independence

Types of Database System Architecture

  • 1-tier, 2-tier, and 3-tier architectures
  • 3-tier architecture separates its tiers from each other based on the basis of users

Database System Levels

  • External level
  • Conceptual level
  • Internal level

Mapping

  • Conceptual/Internal Mapping
  • External/Conceptual Mapping

Database Users and DBA,

  • Application programmers
  • Sophisticated users
  • Specialized users
  • Naive users

Unit 2: Relational Data Model

  • Structure of relational databases
  • Domains
  • Relations
  • Relational algebra-fundamental operators and syntax. Relational algebra queries
  • Entity Relationship Diagram
  • Components of E-R Diagram (Entities, Attributes, Relationships)
  • Mapping cardinalities
  • Keys
  • Extended E-R Features: Specialization, Generalization, and Aggregation

Unit 3: Relational Database Design

  • Anomalies
    • Update Anomaly
    • Insertion Anomaly
    • Deletion Anomaly
  • Functional Dependency
  • Types of Functional Dependency
    • Trivial Functional Dependencies
    • Nontrivial Functional Dependencies
  • Closure of Set of Dependencies
    • Reflexivity
    • Augmentation
    • Transitivity
    • Decomposition
    • Union
    • Composition
  • Normalization
    • First Normal Form (1NF)

Unit 4: Data Manipulation Commands

  • Adding, Updating, Saving, Restoring, and Deleting Table Rows
  • Select Queries with Conditional Restrictions, Arithmetic Operators, and Logical Operators
  • Advanced Data Definition Commands
    • Changing column data types
    • Adding columns
    • Dropping columns
    • Adding Primary and Foreign Keys
  • Data Updates
  • Aggregate Functions
  • SQL Views
  • What is SQL?, SQL commands for creating, altering, and dropping tables

Unit 5: Advanced SQL Set Operators

  • Union, Union All, Intersect, Minus
  • SQL Join Operators: Cross Join, Natural Join,USING clause join, ON clause join, Outer Join
  • Sub-queries: Sub queries IN Sub queries, Having Sub queries
  • Function Date, String Maths Number, SQL data types, SQL string functions(ASC, CONCAT, LENGTH, REVERSE)

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6 Lecture notes (unit wise-may be handwritten)_BCA_DBMS.docx.pdf

Description

This quiz explores key concepts in database design, focusing on multi-valued attributes, entity relationships, and relational schema transformations. Participants will answer questions related to primary keys, aggregations, and best practices in naming tables in database management systems.

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