Relational Database Model Overview
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Relational Database Model Overview

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Questions and Answers

What is a requirement for a primary key in a relational database?

  • It can include null values.
  • All values must be unique. (correct)
  • It must consist of at least three attributes.
  • It can refer to non-existent records.

    • What does referential integrity ensure in a relational database?

  • Duplicate values in attributes are allowed.
  • All values can be null.
  • A foreign key must point to an existing primary key. (correct)
  • Foreign keys do not need to match primary keys.

    • How can controlled redundancy benefit a relational database?

  • By restricting the number of attributes in a table.
  • By enabling tables to link through shared attributes. (correct)
  • By allowing unnecessary duplication of attribute values.
  • By avoiding relationships between tables.

    • What is the purpose of the SELECT operation in relational algebra?

    <p>To filter rows that meet a specified condition.</p> Signup and view all the answers

    Which statement correctly defines a secondary key in a database?

    <p>A key used strictly for data retrieval purposes.</p> Signup and view all the answers

    What is the consequence of using NULL values in attributes of a database?

    <p>They can create logical problems when tables are linked.</p> Signup and view all the answers

    Which of the following is NOT a common relational algebra operator?

    <p>CONCATENATE</p> Signup and view all the answers

    What is the main goal of enforcing entity integrity rules in a database?

    <p>To guarantee each row has a unique identity.</p> Signup and view all the answers

    Why is it important to avoid NULL values in primary key attributes?

    <p>They can lead to ambiguity in record retrieval.</p> Signup and view all the answers

    What defines a foreign key in a relational database?

    <p>A key that conforms to primary key values in a related table.</p> Signup and view all the answers

    What does a composite key consist of in a relational database?

    <p>Multiple attributes that together uniquely identify a row</p> Signup and view all the answers

    Which of the following best describes the concept of functional dependence in a relational database?

    <p>A relationship where all attributes can be determined by a single attribute only</p> Signup and view all the answers

    What is the primary role of keys in a relational database?

    <p>To uniquely identify each row in a table</p> Signup and view all the answers

    Which type of integrity is maintained by ensuring all foreign keys match primary keys in another table?

    <p>Referential integrity</p> Signup and view all the answers

    In relational algebra, which operation is used to combine rows from two or more tables based on a related column?

    <p>Join</p> Signup and view all the answers

    Which of the following statements about tables in a relational database model is true?

    <p>A table represents a collection of related entities in a two-dimensional format.</p> Signup and view all the answers

    What does the data dictionary in a relational database typically contain?

    <p>Information about database structures, including tables and keys</p> Signup and view all the answers

    Which type of join returns only matching rows from both tables involved?

    <p>Inner join</p> Signup and view all the answers

    What characteristic of relational databases allows for changes in data structure without affecting the entire system?

    <p>Structural independence</p> Signup and view all the answers

    Which operation yields only the rows that exist in both tables being combined?

    <p>Inner join</p> Signup and view all the answers

    What is the purpose of using a LEFT OUTER JOIN in a relational database?

    <p>To return unmatched records from one table along with matched ones</p> Signup and view all the answers

    What characteristic must tables have to be used in a UNION operation?

    <p>They must be union-compatible</p> Signup and view all the answers

    Which join type retains unmatched records from both tables, filling in nulls where necessary?

    <p>Outer join</p> Signup and view all the answers

    What do the terms homonym and synonym signify in the context of a data dictionary?

    <p>Homonym means the same name used for multiple attributes; synonym means the use of different names for the same attribute</p> Signup and view all the answers

    Which relational algebra operation yields all possible combinations of rows from two tables?

    <p>Cartesian product</p> Signup and view all the answers

    In a relational database, what type of relationship is the 1:M relationship considered to be?

    <p>Ideal and should be the norm</p> Signup and view all the answers

    The DIVIDE operation in relational algebra enables which of the following?

    <p>Finding all values associated with every row in a single-column table</p> Signup and view all the answers

    What does the term 'referential integrity' in a relational database guard against?

    <p>Data inconsistency between related tables</p> Signup and view all the answers

    Which type of join requires explicit criteria to be defined for matching records?

    <p>Equijoin</p> Signup and view all the answers

    In a relational database, what does an inner join specifically return?

    <p>Only matched records from all tables</p> Signup and view all the answers

    Which of the following must be true for a natural join to occur between two tables?

    <p>The common columns must have the same attribute names and compatible domains</p> Signup and view all the answers

    What type of relationship should rarely exist in a relational database design?

    <p>1:1 relationship</p> Signup and view all the answers

    When breaking an M:N relationship into separate entities, what must be included?

    <p>Foreign keys referencing each related table</p> Signup and view all the answers

    How does an outer join differ from an inner join?

    <p>It retains unmatched records, filling them with nulls</p> Signup and view all the answers

    Study Notes

    Relational Database Model

    • The relational database model uses a logical view of data.
    • The model is based on tables that represent relations.
    • Tables are implemented in a relational database management system (RDBMS).
    • A table consists of rows (tuples) and columns (attributes).
    • Each row in a table represents an entity.
    • A table is a logical representation of the database structure.
    • Data redundancy is handled by sharing common attributes between tables.
    • The relational database model uses keys to identify rows uniquely.
    • A key is a set of attributes that determine other attributes.
    • Functional dependence indicates that the value of one attribute can determine the values of other attributes.
    • A composite key is composed of multiple attributes.
    • A key attribute is any attribute that is part of a key.
    • A superkey uniquely identifies each row.
    • A candidate key is a minimal superkey.
    • A primary key uniquely identifies each row in the table.
    • Each primary key must have unique values and cannot contain a null value.
    • A null value represents an unknown, missing or a "not applicable" attribute value.
    • Controlled redundancy exists when attribute values are duplicated for relational purposes.
    • A foreign key references a primary key value in a related table.
    • Referential integrity ensures that a foreign key is valid.
    • A secondary key is used for data retrieval purposes.
    • Indexing helps to improve database performance by providing an index for retrieval of data.

    Relationships within the Relational Database

    • A 1:M relationship is the ideal relationship in the relational model where one entity is related to many entities.
    • A 1:1 relationship is rarely used and may indicate that two entities should be combined into one table.
    • A M:N relationship cannot be implemented directly. This relationship can be achieved by creating a composite entity using foreign keys to link tables.
    • A composite entity includes foreign keys from the primary keys of the tables to be linked.

    Relational Set Operators

    • Relational operators manipulate table contents and create new relations using relational algebra.
    • SELECT retrieves rows based on certain criteria.
    • PROJECT selects a subset of columns from a table.
    • JOIN merges data from multiple tables based on common columns.
    • UNION combines rows from two tables, excluding duplicates.
    • INTERSECT returns rows that appear in both tables, excluding duplicates.
    • DIFFERENCE returns rows that are in the first table excluding the rows found in the second table.
    • PRODUCT returns all possible combinations of rows from two tables.
    • DIVIDE returns values from a 2-column table(dividend) based on the presence of those values in a single-column table(divisor).

    The Data Dictionary and System Catalog

    • The Data Dictionary contains information about tables within the database.
    • The system catalog provides metadata about all objects in the database.
    • A homonym occurs when different attributes have the same name.
    • A synonym occurs when the same attribute is referred to using different names.

    Data Integrity

    • Entity Integrity: ensures the uniqueness of each row within a table.
    • Referential Integrity: ensures that the foreign keys in a table match existing primary keys in their corresponding table.
    • These integrity rules can be enforced by the RDBMS or implemented within application design.

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    Chapter-3.pdf

    Description

    This quiz covers the fundamental concepts of the relational database model, including its structure based on tables, unique keys, and data redundancy handling. Understand the roles of attributes, tuples, and key types like primary and composite keys to reinforce your knowledge of RDBMS.

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