diff --git a/schemas/Indicator.yaml b/schemas/Indicator.yaml
index 7b158c1..456f079 100644
--- a/schemas/Indicator.yaml
+++ b/schemas/Indicator.yaml
@@ -2,6 +2,16 @@ description: |-
   A single ratio or flat number; should be shown as one box with a chart (generally, a single fixed-size bar with each ratio element rendered on this bar). The numbers in this object are on some axis, generally, percentage.
 type: object
 properties:
+  key:
+    description: Unique identifier, not to be shown to the user, for referring to this indicator in other API calls
+    type: string
+    example: ZEL-dm2-bp-result
+  basedOn:
+    description: |-
+      *OPTIONAL* Refers to the key of another indicator in this set; the data this indicator represents is a calculation
+      based on the population of the referred-to indicator. Not necessarily something that needs to be shown in the user interface.
+    type: string
+    example: ZEL-dm2-bp
   title:
     description: Short, in dutch, *HTML* (but rarely includes formatting; at most, sup/superscript).
     type: string