xDBMLOne schema. Many storage technologies.

xdbml: 0.1

Type Address {
  street  varchar [not null]
  city    varchar [not null]
  country varchar [default: 'US']
}

Container core [type: schema] {
  Entity customers {
    id              int     [pk]
    email           varchar [unique, not null,
                             pattern: '^[^@]+@[^@]+$',
                             tags: ['pii', 'gdpr-subject']]
    primary_address Address
  }
}

Container orders_store [type: database] {
  Collection orders {
    _id          objectId  [pk]
    customer_id  int       [not null]
    placed_at    timestamp [granularity: second]
    line_items   array [
      line_item object {
        sku        varchar [not null]
        quantity   int     [not null, minimum: 1]
        unit_price decimal(10,2)
      }
    ]
    payment_method oneOf {
      card   object { last4 varchar(4), brand varchar }
      bank   object { iban varchar }
      wallet object { provider varchar }
    } [discriminator: method_kind]
  }
}

Ref: orders_store.orders.customer_id        > core.customers.id [source: '1..*', target: '1..1']
Ref: orders_store.orders.line_items.[*].sku > catalog.products.sku