lab4.md

@@ -52,9 +52,12 @@ The following query can be used to retrieve all the elements in the database:
 ```bash
 ros2 service call /kdb_server/sparql_query ros2_kdb_msgs/srv/QueryDatabase "graphname: 'salientpoints'
 format: 'json'
-query: 'SELECT ?x ?y ?z WHERE { ?x ?y ?z }'"
+query: 'SELECT ?subject ?predicate ?object WHERE { ?subject ?predicate ?object }'"
 ```
 
+*Note:* this query should be used to check if any triples was added in the database, it should not be used as a solution in the lab.
+
+
 The following query can be used to retrieve all the object with their class that are near the point of coordinate `(10, 12)`:
 
 ```bash