Relationship Model

Relationship Model

1. Entity

   • Class of objects
   • Described by its attributes
     • Key attribute(s)
     • Composite attribute(s)
     • Multivalued attribute(s)
     • NULL value(s)
     • And more...
       • Derived
       • Alternative key attribute(s)

2. Generalizations

   • Types within an entity
   • Coverage propierties
     • Total or Partial
       • Total: every entity has a type
       • Partial: otherwise
     • Disjoint or Overlapping
       • Disjoint: every entity only has one of the types
       • Overlapping: otherwise

3. Relationship

   • Relation between 2 entities
   • Cardinality
     • One-to-one
     • One-to-many
     • Many-to-many
   • Attributes
     • Can belong to relationships

4. Constraints

   • Mandatory participation
   • No limitations
     • EER to Relational Model
   • Identification Dependency
     • Only in 1:N
     • Entity needs to be identified with the key attribute of the other

5. Types

   • Binary
   • Ternary
     • Existence constraint
       • Affects only one relationship and one entity
   • Reflexive

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