Relationship Terminology

Structural constraints

Cardinality

• The description of how many of one record relate to another and vice-versa
• If a record owns many records, its relationship is said to be ***One-to-many
  • one-to-many can be abbreviated as 1:M
• If a child record may also be owned by multiple people, it is Many-to-many*
  • This can be abbreviated as M:N

Optionality

• Determines if a relationship is required or mandatory
• Determines whether it must have a record relationship in the other file
• Optional
  • Can be described as optional or partial
• Mandatory
  • Can be described as mandatory or full

Describing relationships

• Example:
  • People may have zero or more books,
  • Books must be associated with one and only one person.