diff --git a/src/schema/objects/columns.yaml b/src/schema/objects/columns.yaml
index 5ca387a007..0bcec1bcc4 100644
--- a/src/schema/objects/columns.yaml
+++ b/src/schema/objects/columns.yaml
@@ -603,6 +603,14 @@ stim_file:
     For example `images/cat03.jpg` will be translated to `/stimuli/images/cat03.jpg`.
   type: string
   format: stimuli_relative
+stim_id:
+  name: stim_id
+  display_name: Stimulus ID
+  description: |
+    A stimulus identifier of the form `stim-<label>`,
+    matching a stimulus entity found in `stimuli/` directory.
+  type: string
+  pattern: ^stim-[0-9a-zA-Z]+$
 strain:
   name: strain
   display_name: Strain
diff --git a/src/schema/objects/entities.yaml b/src/schema/objects/entities.yaml
index 6facc34c0d..adfdaf533c 100644
--- a/src/schema/objects/entities.yaml
+++ b/src/schema/objects/entities.yaml
@@ -422,3 +422,22 @@ tracksys:
     may be longer and more human readable.
   type: string
   format: label
+stimulus:
+  name: stim
+  display_name: Stimulus
+  description: |
+    The `stim-<label>` entity can be used to distinguish stimulus files stored in the `stimuli/` directory.
+
+    This entity is only applicable to stimulus files.
+  type: string
+  format: label
+annotation:
+  name: annot
+  display_name: Annotation
+  description: |
+    The `annot-<label>` entity can be used to distinguish different annotations
+    of the stimulus data.
+
+    This entity is only applicable to stimulus files.
+  type: string
+  format: label
diff --git a/src/schema/rules/entities.yaml b/src/schema/rules/entities.yaml
index 2194a61a92..8d86c87d9e 100644
--- a/src/schema/rules/entities.yaml
+++ b/src/schema/rules/entities.yaml
@@ -30,3 +30,5 @@
 - density
 - label
 - description
+- stimulus
+- annotation