Within Sentences, an associative schema comprises:

Entity types, such as  Customer, Address, Country,  Product, Date, Price and so on.

The main property of an entity type is its Data type: Currency, Date, Hyperlink, Image, Number, Percentage, Text, Time, None etc.

Association types:
  Customer, contact, Person
  Customer, places, Order
  Person, mobile phone, Telecom number

The main property of an association type is its Cardinality: Optional, Mandatory; Singular, Multiple.

Both entity and association types may have subsets and supertypes:

Subset: an instance's membership of a subset is transient: eg. 'Employee' may have a subset called 'Manager': individual employees may become managers or cease to be managers.

Supertype: an instance's eg. the entity type Car may have a supertype of Vehicle - a car is a vehicle but it is also essentially and perpetually a car.