3.0

• What does the relational database model offer?

  A logical view of data
• What is the basic component of the relational model?

  Relations
• What are relations composed of?

  Rows (tuples) and columns (attributes)
• How are relations implemented in a relational DBMS?

  As tables
• What do relational database operators help with?

  Manipulating data within the database
• What does the data dictionary provide?

  Detailed accounting of all tables
• How is data redundancy handled in the relational model?

  By using common attributes
• Why is indexing important in databases?

  It improves data retrieval speed
• What is a logical view of data?

  Viewing data without considering physical storage
• What is the structure of a table in a relational database?

  A two-dimensional structure of rows and columns
• What does entity integrity ensure in a table?

  Each primary key value must be unique
• What is a null value in a database?

  A value that indicates no entry
• What is a composite key?

  A key composed of more than one attribute
• What is a foreign key?

  An attribute matching primary key values
• What does referential integrity ensure?

  FK refers to an existing valid tuple
• What is a secondary key used for?

  Strictly for data retrieval purposes
• What is the role of integrity rules in RDBMS?

  To enforce entity and referential integrity
• What does relational algebra define?

  Theoretical way of manipulating table contents
• What is the purpose of the system catalog?

  Describes all objects within the database
• What is a homonym in database terminology?

  Same name for different attributes
• What is a synonym in database terminology?

  Different names for the same attribute
• What is a 1:M relationship?

  One entity relates to many others
• What is a 1:1 relationship?

  One entity related to only one other
• How are M:N relationships implemented?

  By breaking them into 1:M relationships
• What does data redundancy lead to?

  Data anomalies that affect database effectiveness
• What is the purpose of an index in a database?

  To logically access rows in a table
• What is a unique index?

  Index with only one pointer value
• What are the types of keys in a relational database?

  • Primary key
  • Foreign key
  • Composite key
  • Candidate key
  • Superkey
  • Secondary key
• What did Codd publish in 1985?

  A list of 12 rules for relational databases
• What are the main characteristics of a relational database?

  • Tables as basic building blocks
  • Keys define functional dependencies
  • Tables linked by common attributes
  • Supports relational algebra functions
• What are the relationships in a relational database?

  • 1:1 relationship
  • 1:M relationship
  • M:N relationship (converted to 1:M)
• What are the integrity rules in relational databases?

  • Entity integrity
  • Referential integrity
  • Avoiding nulls with flags
• What are the relational set operators?

  • SELECT
  • UNION
  • PROJECT
  • DIFFERENCE
  • JOIN
  • PRODUCT
  • INTERSECT
  • DIVIDE
• What is the significance of the data dictionary and system catalog?

  • Data dictionary: details of all tables
  • System catalog: metadata for all objects
• What are the problems associated with null values in databases?

  • Affect functions like COUNT, AVERAGE, SUM
  • Create logical problems when linking tables
• What is controlled redundancy in relational databases?

  • Necessary for relationships
  • Exists only when duplication is unnecessary
• What are Codd's rules for relational databases?

  • Define minimum standards for relational systems
  • Not fully supported by all vendors
• Unique Index

  A type of index that enforces uniqueness on a set of columns, preventing duplicate values.
• Single-Column Unique Index

  A unique index created on only one column, enforcing uniqueness on that column.
• Primary Key

  A column or set of columns that uniquely identifies each row in a table, enforcing data integrity.