# ComponentSystemBase > A system provides behavior in an ECS architecture. ## Definition * **Type:** Class * **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md) * **Assembly:** UnityEngine.EntitiesModule ```csharp public abstract class ComponentSystemBase ``` ## Remarks System implementations should inherit [SystemBase](/engine/7000.0/script-reference/unity/entities/systembase.md), which is a subclass of ComponentSystemBase. ## Constructors | Constructor | Description | | --------------------------------------------------------------------------------------------------- | ------------------------------------------------ | | [ComponentSystemBase()](/engine/7000.0/script-reference/unity/entities/componentsystembase/ctor.md) | Initializes and returns an instance of a system. | ## Properties | Property | Description | | ------------------------------------------------------------------------------------------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | [Enabled](/engine/7000.0/script-reference/unity/entities/componentsystembase/enabled.md) | Controls whether this system executes when its OnUpdate function is called. | | [EntityManager](/engine/7000.0/script-reference/unity/entities/componentsystembase/entitymanager.md) | The EntityManager object of the [ComponentSystemBase.World](/engine/7000.0/script-reference/unity/entities/componentsystembase/world.md) in which this system exists. | | [EntityQueries](/engine/7000.0/script-reference/unity/entities/componentsystembase/entityqueries.md) | The query objects cached by this system. | | [GlobalSystemVersion](/engine/7000.0/script-reference/unity/entities/componentsystembase/globalsystemversion.md) | The current change version number in this [ComponentSystemBase.World](/engine/7000.0/script-reference/unity/entities/componentsystembase/world.md). | | [LastSystemVersion](/engine/7000.0/script-reference/unity/entities/componentsystembase/lastsystemversion.md) | The current version of this system. | | [SystemHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/systemhandle.md) | The SystemHandle of this system. | | [World](/engine/7000.0/script-reference/unity/entities/componentsystembase/world.md) | The World in which this system exists. | | [WorldUpdateAllocator](/engine/7000.0/script-reference/unity/entities/componentsystembase/worldupdateallocator.md) | Retrieve world update allocator from system state. | ## Methods | Method | Description | | ------------------------------------------------------------------------------------------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | [GetBufferLookup](/engine/7000.0/script-reference/unity/entities/componentsystembase/getbufferlookup.md) | Manually gets a BufferLookup\\\ object that can access a [DynamicBuffer\](/engine/7000.0/script-reference/unity/entities/dynamicbuffer1.md). | | [GetBufferTypeHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/getbuffertypehandle.md) | Manually gets the run-time type information required to access an array of buffer components in a chunk. | | [GetComponentLookup](/engine/7000.0/script-reference/unity/entities/componentsystembase/getcomponentlookup.md) | Manually gets a dictionary-like container containing all components of type T, keyed by Entity. | | [GetComponentTypeHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/getcomponenttypehandle.md) | Manually gets the run-time type information required to access an array of component data in a chunk. | | [GetDynamicComponentTypeHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/getdynamiccomponenttypehandle.md) | Manually gets the run-time type information required to access an array of component data in a chunk. | | [GetDynamicSharedComponentTypeHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/getdynamicsharedcomponenttypehandle.md) | Manually gets the run-time type information required to access a shared component data in a chunk. | | [GetEntityQuery](/engine/7000.0/script-reference/unity/entities/componentsystembase/getentityquery.md) | Gets the cached query for the specified component types, if one exists; otherwise, creates a new query instance and caches it. | | [GetEntityStorageInfoLookup](/engine/7000.0/script-reference/unity/entities/componentsystembase/getentitystorageinfolookup.md) | Manually gets an EntityStorageInfoLookup object that can access a [EntityStorageInfo](/engine/7000.0/script-reference/unity/entities/entitystorageinfo.md). | | [GetEntityTypeHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/getentitytypehandle.md) | Manually gets the run-time type information required to access the array of [Entity](/engine/7000.0/script-reference/unity/entities/entity.md) objects in a chunk. | | [GetSharedComponentTypeHandle](/engine/7000.0/script-reference/unity/entities/componentsystembase/getsharedcomponenttypehandle.md) | Manually gets the run-time type information required to access a shared component data in a chunk. | | [OnCreate](/engine/7000.0/script-reference/unity/entities/componentsystembase/oncreate.md) | Called when this system is created. | | [OnDestroy](/engine/7000.0/script-reference/unity/entities/componentsystembase/ondestroy.md) | Called when this system is destroyed. | | [OnStartRunning](/engine/7000.0/script-reference/unity/entities/componentsystembase/onstartrunning.md) | Called before the first call to OnUpdate and when a system resumes updating after being stopped or disabled. | | [OnStopRunning](/engine/7000.0/script-reference/unity/entities/componentsystembase/onstoprunning.md) | Called when this system stops running because no entities match the system's [EntityQuery](/engine/7000.0/script-reference/unity/entities/entityquery.md) objects or because you change the system [ComponentSystemBase.Enabled](/engine/7000.0/script-reference/unity/entities/componentsystembase/enabled.md) property to false. | | [RequireAnyForUpdate](/engine/7000.0/script-reference/unity/entities/componentsystembase/requireanyforupdate.md) | Provide a set of queries, one of which must match entities for the system to run. | | [RequireForUpdate](/engine/7000.0/script-reference/unity/entities/componentsystembase/requireforupdate.md) | Adds a query that must match entities for the system to run. You can add multiple required queries to a system; all of them must match at least one entity for the system to run. | | [ShouldRunSystem](/engine/7000.0/script-reference/unity/entities/componentsystembase/shouldrunsystem.md) | Reports whether this system satisfies the criteria to update. This function is used internally to determine whether the system's OnUpdate function can be skipped. | | [Update](/engine/7000.0/script-reference/unity/entities/componentsystembase/update.md) | Executes the system immediately. |