diff --git a/tripper/context/0.3/prefixes.yaml b/tripper/context/0.3/prefixes.yaml
index 7e467f3c..0fa32bcf 100644
--- a/tripper/context/0.3/prefixes.yaml
+++ b/tripper/context/0.3/prefixes.yaml
@@ -31,3 +31,4 @@ prefixes:
   emmo: "https://w3id.org/emmo#"
   oteio: "https://w3id.org/emmo/domain/oteio#"
   chameo: "https://w3id.org/emmo/domain/characterisation-methodology/chameo#"
+  ex: "http://www.example.org/"