diff --git a/cyberiadaml.c b/cyberiadaml.c
index c9cee56..2f2a765 100644
--- a/cyberiadaml.c
+++ b/cyberiadaml.c
@@ -17,6 +17,7 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with this program. If not, see https://www.gnu.org/licenses/
+ *
  * ----------------------------------------------------------------------------- */
 
 #include <stdlib.h>
@@ -27,6 +28,7 @@
 #include "cyberiadaml.h"
 
 #define GRAPHML_NAMESPACE_URI 				"http://graphml.graphdrawing.org/xmlns"
+#define GRAPHML_NAMESPACE_URI_YED			"http://www.yworks.com/xml/graphml"
 #define GRAPHML_GRAPHML_ELEMENT				"graphml"
 #define GRAPHML_BERLOGA_SCHEMENAME_ATTR 	"SchemeName"
 #define GRAPHML_GRAPH_ELEMENT				"graph"
@@ -766,21 +768,34 @@ static int cyberiada_decode_cyberiada_xml(xmlNode* root, CyberiadaSM* sm)
 	return CYBERIADA_FORMAT_ERROR;
 }
 
-static int cyberiada_check_graphml_ns(xmlNode* root)
+static int cyberiada_check_graphml_ns(xmlNode* root, CyberiadaXMLFormat* format)
 {
 	xmlNs* ns;
+	int graphml_found = 0;
+	int yed_found = 0;
 	if (!root || !(ns = root->nsDef)) {
 		ERROR("bad GraphML XML NS: null ns ptr\n");
 		return CYBERIADA_XML_ERROR;
 	}
 	do {
 		if (strcmp((const char*)ns->href, GRAPHML_NAMESPACE_URI) == 0) {
-			return CYBERIADA_NO_ERROR;
-		}
+			graphml_found = 1;
+		} else if (strcmp((const char*)ns->href, GRAPHML_NAMESPACE_URI_YED) == 0) {
+			yed_found = 1;
+		}  
 		ns = ns->next;
 	} while (ns);
-	ERROR("no GraphML XML NS href\n");
-	return CYBERIADA_XML_ERROR;
+	if (!graphml_found) {
+		ERROR("no GraphML XML NS href\n");
+		return CYBERIADA_XML_ERROR;
+	}
+	if (*format == cybxmlUnknown && yed_found) {
+		*format = cybxmlYED;
+	} else if (*format == cybxmlYED && !yed_found) {
+		ERROR("no GraphML YED NS href\n");
+		return CYBERIADA_XML_ERROR;
+	}
+	return CYBERIADA_NO_ERROR;
 }
 
 int cyberiada_read_sm(CyberiadaSM* sm, const char* filename, CyberiadaXMLFormat format)
@@ -806,8 +821,8 @@ int cyberiada_read_sm(CyberiadaSM* sm, const char* filename, CyberiadaXMLFormat
 	}
 
 	/* check whether the xml is graphml */
-	if (cyberiada_check_graphml_ns(root)) {
-		ERROR("error: no graphml namespace in %s\n", filename);
+	if (cyberiada_check_graphml_ns(root, &format)) {
+		ERROR("error: no valid graphml namespace in %s\n", filename);
 		return CYBERIADA_XML_ERROR;
 	}
 
@@ -816,8 +831,8 @@ int cyberiada_read_sm(CyberiadaSM* sm, const char* filename, CyberiadaXMLFormat
 	} else if (format == cybxmlCyberiada) {
 		res = cyberiada_decode_cyberiada_xml(root, sm);
 	} else {
-		ERROR("error: unsupported GraphML format %d of file %s\n",
-				format, filename);
+		ERROR("error: unsupported GraphML format of file %s\n",
+			  filename);
 		return CYBERIADA_XML_ERROR;
 	}
 
diff --git a/cyberiadaml.h b/cyberiadaml.h
index 38c7c4b..23f231e 100644
--- a/cyberiadaml.h
+++ b/cyberiadaml.h
@@ -17,6 +17,7 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with this program. If not, see https://www.gnu.org/licenses/
+ *
  * ----------------------------------------------------------------------------- */
 
 #ifndef __CYBERIADA_ML_H
@@ -98,7 +99,8 @@ typedef struct {
 /* SM GraphML supported formats */
 typedef enum {
     cybxmlYED = 0,
-    cybxmlCyberiada
+    cybxmlCyberiada,
+	cybxmlUnknown
 } CyberiadaXMLFormat;
     
 /* -----------------------------------------------------------------------------
diff --git a/test.c b/test.c
index 6f9d982..2f7064a 100644
--- a/test.c
+++ b/test.c
@@ -39,7 +39,7 @@ unsigned int format_count = sizeof(formats) / sizeof(char*);
 static void print_usage(const char* name)
 {
 	unsigned int i;
-	fprintf(stderr, "%s -t <format> <path-to-graphml-file>\n\n", name);
+	fprintf(stderr, "%s [-t <format>] <path-to-graphml-file>\n\n", name);
 	fprintf(stderr, "Supported formats:\n");
 	for (i = 0; i < format_count; i++) {
 		fprintf(stderr, "  %-20s %s\n", formats[i], format_names[i]);
@@ -51,29 +51,35 @@ int main(int argc, char** argv)
 {
     char *filename;
 	char *format_str = "";
-	CyberiadaXMLFormat format;
+	CyberiadaXMLFormat format = cybxmlUnknown;
 	unsigned int i;
 	int res;
 	CyberiadaSM sm;
 
-	if (argc != 4 ||
-		strcmp(argv[1], "-t") != 0) {
+	if (argc == 4) {
+		if (strcmp(argv[1], "-t") != 0) {
+			print_usage(argv[0]);
+			return 1;
+		}
+		for(i = 0; i < format_count; i++) {
+			if (strcmp(argv[2], formats[i]) == 0) {
+				format = (CyberiadaXMLFormat)i;
+				format_str = argv[2];
+				break;
+			}
+		}
+		if(strlen(format_str) == 0) {
+			fprintf(stderr, "unsupported graphml format %s\n", argv[2]);
+			print_usage(argv[0]);
+			return 2;
+		}
+		filename = argv[3];
+	} else if (argc == 2) {
+		filename = argv[1];
+	} else {
 		print_usage(argv[0]);
 		return 1;
 	}
-	for(i = 0; i < format_count; i++) {
-		if (strcmp(argv[2], formats[i]) == 0) {
-			format = (CyberiadaXMLFormat)i;
-			format_str = argv[2];
-			break;
-		}
-	}
-	if(strlen(format_str) == 0) {
-		fprintf(stderr, "unsupported graphml format %s\n", argv[2]);
-		print_usage(argv[0]);
-		return 2;
-	}
-	filename = argv[3];
 	if ((res = cyberiada_read_sm(&sm, filename, format)) != CYBERIADA_NO_ERROR) {
 		fprintf(stderr, "error while reading %s file: %d\n",
 				filename, res);