Glossary
Entity
An entity is and identifier for a discrete “thing” in a game. Each entity has its own unique set of components called a type.
Component
A component is an identifier that can be added to or removed from an entity’s type. An entity is fully defined by its type and its component values.
Type
A type is a set of components that defines an entity’s composition.
Value component
A value component is a component that adds a value (called component data) to an entity.
Component data
Component data is any value attached to an entity through a component.
Tag component
A tag component is a component that does not add data to entities.
World
A world is the container for all ECS data, including entities, entity types and component data, and resources.
Resource
A resource a key that is used to get and set an arbitrary (non-entity related) value within a world. Used synonymously with Resource value.
Resource value
A resource value is a non-entity, non-component piece of game state added to the world through a resource.
System
A system is a function that updates a world’s entities and resources. Systems commonly use queries and monitors to implement game logic and react to entity composition changes.
Query
A query is an iterable object that yields entities matching a set of query terms.
Query term
A query term is any component, relation, or slot.
Monitor
A monitor is a a query-like object that yields entities that began matching or no longer match an array of query terms.
Relation
A relation is a function that returns per-entity relationship components. Relations are subsituted in types with their underlying relation tag.
Relation tag
A relation tag is a tag component automatically given to relations. They provide the means to find all entities with associated relationships.
For example, world.of(ChildOf) would find all entities that are a child of another entity.
Relationship component
A relationship component is the product of calling a relation with an entity. For example, ChildOf(parent) creates a relationship component for the entity parent. When added to an entity, a relation component asserts that it’s entity and the entity to which it is being added are related in some way.
Slot
A slot is a function that builds slot components. Slots are defined with a fixed set of components. A slot can only produce slot components for the components it was defined with.
Slot tag
A slot tag is a tag component automatically given to slots. Slots are subsituted in types with their underlying slot tags. For example, world.of(MovementState) would find all entities with a MovementState.
Slot component
A slot component is the product of calling a slot with a component. For example, MovementState(Running) creates a slot component for the component Running. When added to an entity, a slot component asserts that it’s entity may have only one slot component of the given slot.