4.0

• What does the ER model form the basis of?

  ER diagram
• What does an ERD represent?

  Conceptual database as viewed by end user
• What are the main components depicted in ERDs?

  • Entities
  • Attributes
  • Relationships
• What does the term "entities" refer to in database context?

  Entity set, not single occurrence
• How is an entity represented in Chen and Crow’s Foot models?

  By a rectangle with entity’s name
• How is the entity name formatted?

  Written in capital letters
• What are attributes in the context of entities?

  Characteristics of entities
• How are attributes represented in Chen notation?

  By ovals connected to entity rectangle
• How are attributes represented in Crow’s Foot notation?

  Written in attribute box below entity rectangle
• What is a required attribute?

  Must have a value
• What is an optional attribute?

  May be left empty
• What is a domain in relation to attributes?

  Set of possible values for an attribute
• What are identifiers in database terms?

  Attributes that uniquely identify each entity instance
• What is a composite identifier?

  Primary key composed of more than one attribute
• What is a composite attribute?

  Can be subdivided into smaller attributes
• What is a simple attribute?

  Cannot be subdivided
• What is a single-value attribute?

  Can have only a single value
• What are multivalued attributes?

  Can have many values
• What should be done with M:N relationships and multivalued attributes?

  They should not be implemented
• What is a derived attribute?

  Value may be calculated from other attributes
• What is the definition of a relationship in database terms?

  Association between entities
• Who are the participants in a relationship?

  Entities that participate in a relationship
• How do relationships between entities operate?

  Always operate in both directions
• What is a 1:M relationship?

  One entity is associated with many others
• Why is relationship classification difficult?

  If only one side of the relationship is known
• What does connectivity describe in database relationships?

  Relationship classification
• What does cardinality express?

  Minimum and maximum number of entity occurrences
• How are connectivity and cardinality established?

  By concise statements known as business rules
• What is existence dependence in database terms?

  Entity exists only when associated with another
• What is existence independence?

  Entity can exist apart from related entities
• What are weak relationships?

  PK of related entity does not contain PK component of parent entity
• What are strong relationships?

  PK of related entity contains PK component of parent entity
• What conditions must a weak entity meet?

  Existence-dependent and PK derived from parent
• Who determines if an entity is weak?

  Database designer based on business rules
• What is optional participation in relationships?

  One entity occurrence does not require another
• What is mandatory participation in relationships?

  One entity occurrence requires corresponding occurrence
• What does relationship degree indicate?

  Number of entities associated with a relationship
• What is a unary relationship?

  Association maintained within a single entity
• What is a binary relationship?

  Association between two entities
• What is a ternary relationship?

  Association involving three entities