diff --git a/debian/var/models/XMLSchema example (in progress) b/debian/var/models/XMLSchema example (in progress)
index f0c4733..be0591c 100644
--- a/debian/var/models/XMLSchema example (in progress)	
+++ b/debian/var/models/XMLSchema example (in progress)	
@@ -2,7 +2,7 @@
 <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
 <!-- https://www.w3schools.com/xml/el_attribute.asp  -->
-<!-- use="required" should be allowed ?!-->
+<!-- use="required" is NOT allowed in attributes declarations-->
 
 <xs:attribute name="id" type="xs:string"/>
 <xs:attribute name="date" type="xs:integer"/>  <!--TODO  type ? -->
@@ -12,11 +12,11 @@
 <xs:attribute name="version" type="xs:float"/>
 <xs:attribute name="owner_id" type="xs:integer"/>
 
-<xs:attribute name="x"  type="xs:integer"/>
-<xs:attribute name="y"  type="xs:integer"/>
-<xs:attribute name="z"  type="xs:integer"/>
-<xs:attribute name="site"  type="xs:integer"/>
-<xs:attribute name="weight"  type="xs:integer"/>
+<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:element name="gem-graph-model">
 <xs:complexType>
@@ -30,7 +30,7 @@
 
             <xs:element name="name">
                 <xs:complexType>
-                    <xs:attribute name="value"  type="xs:string"/>
+                    <xs:attribute name="value"  type="xs:string" use="required"/>
                 </xs:complexType>
             </xs:element>
 
@@ -52,13 +52,13 @@
 
                     <xs:element name="max_thread">
                         <xs:complexType>
-                            <xs:attribute ref="value"/>
+                            <xs:attribute ref="value" use="required"/>
                         </xs:complexType>
                     </xs:element>
 
                     <xs:element name="max_cycles">
                         <xs:complexType>
-                            <xs:attribute ref="value"/>
+                            <xs:attribute ref="value" use="required"/>
                         </xs:complexType>
                     </xs:element>
 
@@ -72,19 +72,19 @@
 
                     <xs:element name="dimension">
                         <xs:complexType>
-                            <xs:attribute ref="value"/>
+                            <xs:attribute ref="value" use="required"/>
                         </xs:complexType>
                     </xs:element>
 
                     <xs:element name="size">
                         <xs:complexType>
-                            <xs:attribute ref="value"/>
+                            <xs:attribute ref="value" use="required"/>
                         </xs:complexType>
                     </xs:element>
 
                     <xs:element name="site_multiplicity">
                         <xs:complexType>
-                            <xs:attribute ref="value"/>
+                            <xs:attribute ref="value" use="required"/>
                         </xs:complexType>
                     </xs:element>
 
@@ -98,9 +98,9 @@
           </xs:element>
 
           </xs:sequence>
-          <xs:attribute ref="id"/>
-          <xs:attribute ref="date"/>
-          <xs:attribute ref="author"/>
+          <xs:attribute ref="id" use="required"/>
+          <xs:attribute ref="date" use="required"/>
+          <xs:attribute ref="author" use="required"/>
           </xs:complexType>
       </xs:element>
 
@@ -110,18 +110,18 @@
 
               <xs:element name="arrow">
                   <xs:complexType>
-                      <xs:attribute ref="x"/>
-                      <xs:attribute ref="y"/>
-                      <xs:attribute ref="z"/>
-                      <xs:attribute ref="site"/>
-                      <xs:attribute ref="weight"/>
+                      <xs:attribute ref="x" use="required"/>
+                      <xs:attribute ref="y" use="required"/>
+                      <xs:attribute ref="z" use="required"/>
+                      <xs:attribute ref="site" use="required"/>
+                      <xs:attribute ref="weight" use="required"/>
                   </xs:complexType>
               </xs:element>
 
           </xs:sequence>
-          <xs:attribute ref="id"/>
-          <xs:attribute ref="date"/>
-          <xs:attribute ref="author"/>
+          <xs:attribute ref="id" use="required"/>
+          <xs:attribute ref="date" use="required"/>
+          <xs:attribute ref="author" use="required"/>
           </xs:complexType>
       </xs:element>