clarify owl:import in data graph

Author: YoucTagh

shacl12-core/index.html

@@ -2534,6 +2534,10 @@ <h3>Data Graph</h3>
 					The data graph is expected to include all the ontology axioms related to the data and especially all the
 					<code>rdfs:subClassOf</code> triples in order for SHACL to correctly identify class targets and validate Core SHACL constraints.
 				</p>
+				<p class="note">
+					`owl:import` in the data graph is not enacted, in order to avoid uncontrolled increase of validation work. If you want to validate 
+					several related ontologies, pass all of them to the SHACL processor (together or one by one), do not rely on `owl:import` links.
+				</p>
 			</section>
 
 			<section id="sh-shapes-graph">