diff --git a/examples/UC3-ECG.ttl b/examples/UC3-ECG.ttl
index fe77d1bb3698d2bfb1277a49d4bf0a4c4d4c3012..7098f0aef0eca94fefbdfd6adfa35147e3f25a1c 100644
--- a/examples/UC3-ECG.ttl
+++ b/examples/UC3-ECG.ttl
@@ -7,6 +7,7 @@
 @prefix s4ehaw: <https://saref.etsi.org/saref4ehaw/> .
 @prefix s4envi: <https://saref.etsi.org/saref4envi/> .
 @prefix s4wear: <https://saref.etsi.org/saref4wear/> .
+@prefix ssn-system: <http://www.w3.org/ns/ssn/systems/> .
 @base <https://saref.etsi.org/saref4ehaw/examples/UC3-ECG/> .