3.1

• 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 in the relational database model?

  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 is the purpose of the data dictionary?

  To provide detailed accounting of all tables
• How is data redundancy handled in the relational database model?

  By using common attributes shared by tables
• Why is indexing important in a database?

  It allows for orderly access to rows
• What does the relational model allow regarding data representation?

  Logical view rather than physical view
• What does a relation represent in a relational database?

  A persistent representation of logical relation
• What must each row in a table be?

  Uniquely identifiable
• What is a key in a relational database?

  One or more attributes that determine others
• What does functional dependence mean in a relational database?

  Attribute B depends on attribute A
• What is the shorthand notation for "A determines B"?

  A → B
• What does it mean if A determines B, C, and D?

  A → B, C, D
• What is a table in the context of a relational database?

  A two-dimensional structure of rows and columns
• What is a composite key?

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

  Any key that uniquely identifies each row
• What is a candidate key?

  A superkey without unnecessary attributes
• What is entity integrity in a table?

  Each primary key value must be unique
• What is not permitted in the primary key to maintain entity integrity?

  A null value
• What does a null represent in a database?

  No value at all
• What can a null indicate in a database?

  An unknown or missing attribute value
• What can create problems when using functions like COUNT or AVERAGE?

  Null values in the database
• What is controlled redundancy in a relational database?

  Redundancy that enables tables to be linked
• What is a foreign key (FK)?

  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?

  Data retrieval purposes only
• What do many RDBMs enforce automatically?

  Integrity rules
• What is safer than relying on automatic enforcement of integrity rules?

  Ensuring application design conforms to rules
• What do designers use to avoid nulls?

  Flags indicating absence of some value
• What does relational algebra define?

  Theoretical way of manipulating table contents
• What do relational algebra operators produce?

  New relations from existing relations
• What does the data dictionary contain?

  Attribute names and characteristics for each table
• What is metadata in the context of a data dictionary?

  Data about data
• What does a homonym indicate?

  Same name for different attributes
• What does a synonym indicate?

  Different names for the same attribute
• What is the ideal relationship in relational modeling?

  1:M relationship
• What should be rare in relational database design?

  1:1 relationship
• What is the norm in any database environment?

  1:M relationship