Fixes wrong XML id name creation

Signed-off-by: Rene-Pascal Fischer <rene-pascal.fischer@iese.fraunhofer.de>
Change-Id: Ic59aff9675ae16b845c397c550b50535450168cd
diff --git a/sdks/java/basys.sdk/src/main/java/org/eclipse/basyx/aas/factory/aasx/AASXFactory.java b/sdks/java/basys.sdk/src/main/java/org/eclipse/basyx/aas/factory/aasx/AASXFactory.java
index 28cf3bb..d25d48e 100644
--- a/sdks/java/basys.sdk/src/main/java/org/eclipse/basyx/aas/factory/aasx/AASXFactory.java
+++ b/sdks/java/basys.sdk/src/main/java/org/eclipse/basyx/aas/factory/aasx/AASXFactory.java
@@ -148,7 +148,9 @@
 	 * @return UUID
 	 */
 	private static String createUniqueID() {
-		return UUID.randomUUID().toString();
+		// only letters or underscore as start of id allowed
+		// https://www.w3.org/TR/1999/REC-xml-names-19990114/#ns-qualnames
+		return "id_" + UUID.randomUUID().toString();
 	}
 	
 	/**