# Quantity¶

- Category
- RigidSortal
- Provides identity
- yes
- Identity principle
- simple
- Rigidity
- rigid
- Dependency
- optional
- Allowed supertypes
- Category, Mixin
- Allowed subtypes
- Subkind, Phase, Role
- Forbidden associations
- ComponentOf, Derivation, Structuration, SubCollectionOf
- Abstract
- undefined

## Definition¶

The «Quantity» construct is used to represent rigid concepts that provide an identity principle for their instances. A «Quantity» represent uncountable things, like Water, Clay, or Beer. It represents a maximally topologically connected amount of matter. Quantities only have other quantities as parts (see the «SubQuantityOf» relation for more details about members of collections). Here are some examples:

An easy way to decide whether a concept is a quantity or not, as yourself this: if you physically divide an instance of ‘x’ in two parts, are the resulting individuals two new instances of x? What if you divide another 5 or 10 times? If the answer is always yes, ‘x’ is a Quantity. To exemplify, let’s think about an pile of sand. If you divide the pile in two, you now have to new piles of sand, right? What if you do that again for each remaining part? We would have 4 piles of sand.

As the other identity provider stereotypes («Kind», «Collective», «Relator» and «Mode»), a Quality can be specialized by subkinds, phases and roles, as well as generalized by mixins and categories.

## Constraints¶

**C1:** A «Quantity» cannot have an identity provider («Kind», «Collective», «Quantity», «Relator», «Mode» and «Quantity») as its direct or indirect super-type.

**C2:** A «Quantity» cannot have types that inherit identity («Subkind», «Role» and «Phase») as its direct or indirect super-types.

**C3:** A «Quantity» cannot have types that aggregate individuals with different identity principles («Category», «RoleMixin» and «Mixin») as its direct or indirect subtypes.

**C4:** As a rigid type, a «Quantity» cannot have any anti-rigid type («Role», «RoleMixin» and «Phase») as its direct or indirect super-type.

## Common questions¶

Ask us some question if something is not clear …

## Examples¶

*No examples yet…*