xdbml: 0.5

// ---------------------------------------------------------------------------
// Supertype groups: two axes, three levels, mixed strategies.
//
// A logical model of parties (spec 12, Appendix C.5). Party is specialized
// along two independent axes: its legal nature (a Person or an Organization,
// never both, and always one of them) and its business role (a Customer, a
// Supplier, both or neither). Person is specialized a second time by the
// role a person plays in the workforce.
//
// Each subtype declares only its own attributes (12.5). The attributes of
// Party apply to every Person, Organization, Customer, Supplier, Employee and
// Contractor without being declared again; where they end up in stored
// structures is decided when a physical model is derived, following the
// materialization settings (12.7):
//   - legal_nature asks for a flat roll-up with a discriminator named `nature`
//   - business_role is overlapping, so it states no discriminator
//   - person_role states no strategy for the group; the Contractor pair
//     asks for roll-down, the Employee pair is left to the derivation tool
//
// Organization declares a key of its own, which `owns` targets. Employee
// declares none, so `assigned` names Employee as an entity-level endpoint
// (11.16) and the derivation supplies the key it refers to.
// ---------------------------------------------------------------------------

Project party_model {
  Note: 'Logical model: parties, their legal nature and business roles, and the people who work for us.'
}

Entity Party {
  party_id   int       [pk]
  name       varchar   [not null]
  email      varchar
  created_at timestamp [not null]
}

Entity Person {
  birth_date  date
  national_id varchar [unique]
}

Entity Organization {
  tax_number varchar [pk]
  legal_form varchar
}

Entity Customer {
  customer_since date
  credit_limit   decimal(12,2)
}

Entity Supplier {
  payment_terms varchar
}

Entity Employee {
  employee_number varchar [unique, not null]
  hire_date       date
}

Entity Contractor {
  agency     varchar
  daily_rate decimal(10,2)
}

Entity Assignment {
  assignment_id int     [pk]
  employee_id   int     [not null]
  project       varchar
}

Entity Truck {
  truck_id  int     [pk]
  plate     varchar [not null]
  owner_tax varchar
}

SupertypeGroup legal_nature [
  supertype: Party,
  completeness: total,
  exclusivity: disjoint,
  strategy: roll_up,
  merge: flat,
  discriminator: nature,
  note: 'Every party is a person or an organization, never both'
] {
  Person
  Organization
}

SupertypeGroup business_role [
  supertype: Party,
  completeness: partial,
  exclusivity: overlapping,
  strategy: preserved_hierarchy
] {
  Customer
  Supplier
}

SupertypeGroup person_role [supertype: Person, completeness: partial, exclusivity: disjoint] {
  Employee
  Contractor [strategy: roll_down]
}

Ref owns: Truck.owner_tax > Organization.tax_number [source: '0..*', target: '0..1']
Ref assigned: Assignment.employee_id > Employee [source: '0..*', target: '1..1']