diff --git a/debian/var/models/example.xmls b/debian/var/models/example.xmls
deleted file mode 100644
index 3d17c89..0000000
--- a/debian/var/models/example.xmls
+++ /dev/null
@@ -1,184 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
-<!-- https://www.freeformatter.com/xml-validator-xsd.html -->
-<!-- https://www.w3schools.com/xml/el_attribute.asp  -->
-<xs:attribute name="id" type="xs:string"/>
-<xs:attribute name="date" type="xs:integer"/>
-<xs:attribute name="name" type="xs:string"/>
-<xs:attribute name="lang" type="xs:string"/>
-<xs:attribute name="owner" type="xs:string"/>
-<xs:attribute name="owner_id" type="xs:integer"/>
-<xs:attribute name="author" type="xs:string"/>
-<xs:attribute name="version" type="xs:float"/>
-<xs:attribute name="sequence" type="xs:integer"/>
-<xs:attribute name="probability" type="xs:integer"/>
-<xs:attribute name="parent" type="xs:string"/>
-
-
-<xs:attributeGroup name="id_date_author">
-      <xs:attribute ref="id"/>
-      <xs:attribute ref="date"/>
-      <xs:attribute ref="author"/>
-</xs:attributeGroup>
-
-<xs:element name="ref">
-    <xs:complexType>
-        <xs:simpleContent>
-            <xs:extension base="xs:string">
-              <xs:attributeGroup ref="id_date_author"/>
-              <xs:attribute ref="lang" use="required"/>
-            </xs:extension>
-        </xs:simpleContent>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="quote" substitutionGroup="ref"/>
-
-<xs:element name="arrow">
-    <xs:complexType>
-        <xs:sequence>
-            <xs:element minOccurs="0" ref="quote"/>
-        </xs:sequence>
-        <xs:attribute name="x" type="xs:integer" default="1"/>
-        <xs:attribute name="y" type="xs:integer" default="0"/>
-        <xs:attribute name="z" type="xs:integer" default="0"/>
-        <xs:attribute name="site" type="xs:integer" default="1"/>
-        <xs:attribute name="weight" type="xs:integer" default="0"/>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="state">
-    <xs:complexType>
-    <xs:sequence minOccurs="1" maxOccurs="unbounded">
-        <xs:element ref="arrow"/>
-    </xs:sequence>
-    <xs:attributeGroup ref="id_date_author"/>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="object" substitutionGroup="state"/>
-
-<xs:element name="space">
-    <xs:complexType>
-    <xs:sequence minOccurs="1" maxOccurs="unbounded">
-        <xs:element ref="arrow"/>
-    </xs:sequence>
-    <xs:attributeGroup ref="id_date_author"/>
-    <xs:attribute ref="sequence" use="required"/>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="if">
-    <xs:complexType>
-    <xs:sequence minOccurs="0" maxOccurs="unbounded">
-        <xs:element minOccurs="0" ref="quote"/>
-        <xs:element ref="arrow"/>
-    </xs:sequence>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="then">
-    <xs:complexType>
-    <xs:sequence minOccurs="0" maxOccurs="unbounded">
-        <xs:element minOccurs="0" ref="quote"/>
-        <xs:element ref="arrow"/>
-    </xs:sequence>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="transition">
-    <xs:complexType>
-        <xs:sequence minOccurs="1" maxOccurs="1">
-            <xs:element minOccurs="0" ref="quote"/>
-            <xs:element ref="if"/>
-            <xs:element ref="then"/>
-        </xs:sequence>
-        <xs:attributeGroup ref="id_date_author"/>
-        <xs:attribute ref="parent" use="required"/>
-        <xs:attribute ref="probability" use="required"/>
-    </xs:complexType>
-</xs:element>
-
-<xs:element name="gem-graph-model">
-<xs:complexType>
-<xs:sequence>
-    <xs:element name="identity">
-        <xs:complexType>
-          <xs:sequence>
-              <xs:element name="name" type="xs:string"/>
-              <xs:element name="owner" type="xs:string"/>
-              <xs:element name="owner_id" type="xs:integer"/>
-              <xs:element name="date" type="xs:integer"/>
-              <xs:element name="version" type="xs:float"/>
-              <xs:element minOccurs="0" ref="ref"/>
-          </xs:sequence>
-        </xs:complexType>
-    </xs:element>
-
-        <xs:element name="parameters">
-        <xs:complexType>
-        <xs:sequence>
-
-            <xs:element name="simulation">
-                <xs:complexType>
-                <xs:sequence>
-
-                    <xs:element name="max_thread"/>
-
-                    <xs:element name="max_cycles"/>
-
-                </xs:sequence>
-                </xs:complexType>
-            </xs:element>
-
-            <xs:element name="space-param">
-                <xs:complexType>
-                <xs:sequence>
-
-                    <xs:element name="dimension"/>
-
-                    <xs:element name="size"/>
-
-                    <xs:element name="site_multiplicity"/>
-
-              </xs:sequence>
-              </xs:complexType>
-          </xs:element>
-
-          </xs:sequence>
-          <xs:attributeGroup ref="id_date_author"/>
-          </xs:complexType>
-      </xs:element>
-
-      <xs:element name="objects">
-          <xs:complexType>
-          <xs:sequence minOccurs="1" maxOccurs="unbounded">
-              <xs:element ref="state"/>
-          </xs:sequence>
-          <xs:attributeGroup ref="id_date_author"/>
-          </xs:complexType>
-      </xs:element>
-
-      <xs:element name="savestates">
-          <xs:complexType>
-          <xs:sequence minOccurs="0" maxOccurs="unbounded">
-              <xs:element ref="space"/>
-          </xs:sequence>
-          <xs:attributeGroup ref="id_date_author"/>
-          </xs:complexType>
-      </xs:element>
-
-      <xs:element name="transitions">
-          <xs:complexType>
-          <xs:sequence minOccurs="0" maxOccurs="unbounded">
-              <xs:element ref="transition"/>
-          </xs:sequence>
-          <xs:attributeGroup ref="id_date_author"/>
-          </xs:complexType>
-      </xs:element>
-
-</xs:sequence>
-<xs:attribute ref="version" use="required"/>
-</xs:complexType>
-</xs:element>
-</xs:schema>
diff --git a/debian/var/models/schemas/model_0.1.xmls b/debian/var/models/schemas/model_0.1.xmls
index fbc0094..3d17c89 100644
--- a/debian/var/models/schemas/model_0.1.xmls
+++ b/debian/var/models/schemas/model_0.1.xmls
@@ -1,5 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
+<!-- https://www.freeformatter.com/xml-validator-xsd.html -->
+<!-- https://www.w3schools.com/xml/el_attribute.asp  -->
 <xs:attribute name="id" type="xs:string"/>
 <xs:attribute name="date" type="xs:integer"/>
 <xs:attribute name="name" type="xs:string"/>
@@ -13,15 +15,17 @@
 <xs:attribute name="parent" type="xs:string"/>
 
 
-<xs:element name="a_string" type="xs:string"/>
+<xs:attributeGroup name="id_date_author">
+      <xs:attribute ref="id"/>
+      <xs:attribute ref="date"/>
+      <xs:attribute ref="author"/>
+</xs:attributeGroup>
 
 <xs:element name="ref">
     <xs:complexType>
         <xs:simpleContent>
             <xs:extension base="xs:string">
-              <xs:attribute ref="id"/>
-              <xs:attribute ref="date"/>
-              <xs:attribute ref="author"/>
+              <xs:attributeGroup ref="id_date_author"/>
               <xs:attribute ref="lang" use="required"/>
             </xs:extension>
         </xs:simpleContent>
@@ -48,9 +52,7 @@
     <xs:sequence minOccurs="1" maxOccurs="unbounded">
         <xs:element ref="arrow"/>
     </xs:sequence>
-    <xs:attribute ref="id" use="required"/>
-    <xs:attribute ref="date" use="required"/>
-    <xs:attribute ref="author" use="required"/>
+    <xs:attributeGroup ref="id_date_author"/>
     </xs:complexType>
 </xs:element>
 
@@ -61,9 +63,7 @@
     <xs:sequence minOccurs="1" maxOccurs="unbounded">
         <xs:element ref="arrow"/>
     </xs:sequence>
-    <xs:attribute ref="id" use="required"/>
-    <xs:attribute ref="date" use="required"/>
-    <xs:attribute ref="author" use="required"/>
+    <xs:attributeGroup ref="id_date_author"/>
     <xs:attribute ref="sequence" use="required"/>
     </xs:complexType>
 </xs:element>
@@ -93,11 +93,9 @@
             <xs:element ref="if"/>
             <xs:element ref="then"/>
         </xs:sequence>
-    <xs:attribute ref="id" use="required"/>
-    <xs:attribute ref="date" use="required"/>
-    <xs:attribute ref="author" use="required"/>
-    <xs:attribute ref="parent" use="required"/>
-    <xs:attribute ref="probability" use="required"/>
+        <xs:attributeGroup ref="id_date_author"/>
+        <xs:attribute ref="parent" use="required"/>
+        <xs:attribute ref="probability" use="required"/>
     </xs:complexType>
 </xs:element>
 
@@ -148,9 +146,7 @@
           </xs:element>
 
           </xs:sequence>
-          <xs:attribute ref="id" use="required"/>
-          <xs:attribute ref="date" use="required"/>
-          <xs:attribute ref="author" use="required"/>
+          <xs:attributeGroup ref="id_date_author"/>
           </xs:complexType>
       </xs:element>
 
@@ -159,9 +155,7 @@
           <xs:sequence minOccurs="1" maxOccurs="unbounded">
               <xs:element ref="state"/>
           </xs:sequence>
-          <xs:attribute ref="id" use="required"/>
-          <xs:attribute ref="date" use="required"/>
-          <xs:attribute ref="author" use="required"/>
+          <xs:attributeGroup ref="id_date_author"/>
           </xs:complexType>
       </xs:element>
 
@@ -170,9 +164,7 @@
           <xs:sequence minOccurs="0" maxOccurs="unbounded">
               <xs:element ref="space"/>
           </xs:sequence>
-          <xs:attribute ref="id" use="required"/>
-          <xs:attribute ref="date" use="required"/>
-          <xs:attribute ref="author" use="required"/>
+          <xs:attributeGroup ref="id_date_author"/>
           </xs:complexType>
       </xs:element>
 
@@ -181,9 +173,7 @@
           <xs:sequence minOccurs="0" maxOccurs="unbounded">
               <xs:element ref="transition"/>
           </xs:sequence>
-          <xs:attribute ref="id" use="required"/>
-          <xs:attribute ref="date" use="required"/>
-          <xs:attribute ref="author" use="required"/>
+          <xs:attributeGroup ref="id_date_author"/>
           </xs:complexType>
       </xs:element>