diff --git a/models/dimers random walk.xml b/models/dimers random walk.xml
index 16439a2..dd1e7a1 100644
--- a/models/dimers random walk.xml	
+++ b/models/dimers random walk.xml	
@@ -1,22 +1,20 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gem-graph-model version="0.2">
-    <!-- Model identity informations -->
     <identity>
        <name>Modèle de test</name>
 
-       <owner>Gaston Lagaffe</owner>
+       <owner>Léontine Patinette</owner>
 
        <owner_id>2</owner_id>
 
-       <date>1629830000</date>
+       <date>1630000000</date>
 
        <version>1.0</version>
 
-       <g_ref id="texte" date="1629830000" author="Jean" lang="en">Ref</g_ref>
+       <g_ref id="Cause" date="1630000000" author="toujours" lang="en">Ref</g_ref>
     </identity>
 
-    <!-- Model parameters -->
-    <parameters id="texte" date="0" author="Gaston Lagaffe">
+    <parameters id="texte" date="0" author="Léontine Trottine.">
         <simulation>
             <max_thread>0</max_thread>
             <max_cycles>9</max_cycles>
@@ -24,18 +22,19 @@
         </simulation>
 
         <space-param>
-            <dimension>
     <!-- loop_on_zero="true"  anything moved before zero reenters at the end of space-->
     <!-- loop_on_zero="false" anything moved before zero is lost-->
     <!-- loop_on_max="true"   anything moved beyond max reenters at the zero of space-->
     <!-- loop_on_max="false"  anything moved beyond max is lost-->
-                <axis name="x" size="29"/>
-                <axis name="y" size="0"/>
-                <axis name="z" size="0"/>
+    
+            <dimension>
+                <coord axis="x" at="29"/>
             </dimension>
+            
             <!-- Site_multiplicity = number of  sites in a space unit. -->
             <!-- Each site points towards a neighbouring space unit. -->
             <!-- Several arrows can be stacked in the same site. -->
+            
             <site_multiplicity>3</site_multiplicity>
 
         </space-param>
@@ -43,50 +42,50 @@
     </parameters>
 
     <!-- Model objects definition -->
-    <objects id="texte" date="1629830000" author="Jean Sirmai">
-        <object id="dimer 1-1" date="1629830000" author="Jean Sirmai">
-            <arrow x="0" y="0" z="0" site="1" weight="1"/>
-            <arrow x="1" y="0" z="0" site="2" weight="1"/>
-
+    
+    <objects id="only dimers in this model" date="1630000000" author="inanimés,... âme ?">
+        <object id="a dimer" date="1630000000" author="Alphonse">
+            <arrow site="1" weight="1"><coord axis="x" at="0"/></arrow>
+            <arrow site="2" weight="1"><coord axis="x" at="1"/></arrow>
         </object>
 
     </objects>
 
+    
     <!-- Saved space description (initial space is sequence 0) -->
-    <savestates id="texte" date="1629830000" author="THE MATRIX">
-      <space id="initial" date="1629830000" author="Jean Sirmai" sequence="0">
-          <arrow x="0"  y="0" z="0" site="1" weight="1"/>
-          <arrow x="1"  y="0" z="0" site="2" weight="1"/>
-
-          <arrow x="10" y="0" z="0" site="1" weight="1"/>
-          <arrow x="11" y="0" z="0" site="2" weight="1"/>
-
-          <arrow x="20" y="0" z="0" site="1" weight="1"/>
-          <arrow x="21" y="0" z="0" site="2" weight="1"/>
-
+    
+    <savedstates id="texte" date="1630000000" author="Qui courrait dans l'herbe'">
+        <state id="initial" date="1630000000" author="Une souris verte">
+            <arrow site="1" weight="1"><coord axis="x" at="0"/></arrow>
+            <arrow site="2" weight="1"><coord axis="x" at="1"/></arrow>
+            <arrow site="1" weight="1"><coord axis="x" at="10"/></arrow>
+            <arrow site="2" weight="1"><coord axis="x" at="11"/></arrow>
+            <arrow site="1" weight="1"><coord axis="x" at="20"/></arrow>
+            <arrow site="2" weight="1"><coord axis="x" at="21"/></arrow>
+            
           <!-- Three dimers 1-1 are drawn in the global space
                at locations (0,1) (10,11) and (20,21) -->
 
-      </space>
+      </state>
 
-    </savestates>
+    </savedstates>
 
     <!-- Model transitions definition (rules) -->
     <!-- In this version : <xs:sequence minOccurs="0" maxOccurs="unbounded">-->
     <!-- Transitions should be edited by hand and written in a 'human-readable' format -->
 
-    <conditions id="random walk of dimers" date="1629822222" author="Jean">
+    <conditions id="random walk of dimers" date="1630000000" author="Zazard le lézard !">
 
-        <condition x= "0" y="0" z="0" site="1" weight="1" node_id="1" parent="0"/>
-        <condition x= "1" y="0" z="0" site="2" weight="1" node_id="2" parent="1"/>
-        <!-- as soon as conditions 1 and 2 are satisfied, a dimer is identified at location (0,1). -->
+        <condition site="1" weight="1" node_id="1" parent="0"><coord axis="x" at="0"/></condition>
+        <condition site="2" weight="1" node_id="2" parent="1"><coord axis="x" at="1"/></condition>
+        <!-- as soon as conditions 1 and 2 are satisfied, a dimer is identified at atation (0,1). -->
 
-        <condition x= "2" y="0" z="0" site="1" weight="0" node_id="3" parent="2"/>
+        <condition site="1" weight="0" node_id="3" parent="2"><coord axis="x" at="2"/></condition>
         <!-- as soon as condition 3 is satisfied,
              the neighbouring space unit to East of the dimer is empty
              and the dimer identified by conditions (1,2)  can be moved to East. -->
 
-        <condition x="-1" y="0" z="0" site="2" weight="0" node_id="4" parent="2"/>
+        <condition site="2" weight="0" node_id="4" parent="2"><coord axis="x" at="-1"/></condition>
         <!-- as soon as condition 4 is satisfied,
              the neighbouring space unit to West of the dimer is empty
              and  the dimer identified by conditions (1,2) can be moved to West. -->
@@ -95,27 +94,26 @@
 
     <transitions>
 
-      <transition id="move_a_dimer_to_east" date="1629811111" author="Jean"
+        <transition id="move_a_dimer_to_east" date="1630000000" author="Pas moi..."
                   parent="3" probability="1">
 
-          <arrow x="0" y="0" z="0" site="1" weight="0"/>
-          <arrow x="1" y="0" z="0" site="2" weight="0"/>
-          <arrow x="1" y="0" z="0" site="1" weight="1"/>
-          <arrow x="2" y="0" z="0" site="2" weight="1"/>
+            <arrow site="1" weight="0"><coord axis="x" at="0"/></arrow>
+            <arrow site="2" weight="0"><coord axis="x" at="1"/></arrow>
+            <arrow site="1" weight="1"><coord axis="x" at="1"/></arrow>
+            <arrow site="2" weight="1"><coord axis="x" at="2"/></arrow>
 
       </transition>
 
-      <transition id="move_a_dimer_to_west" date="1629811112" author="Jean"
+      <transition id="move_a_dimer_to_west" date="1630000000" author="Ni moi !"
                   parent="4" probability="1">
 
-          <arrow x= "0" y="0" z="0" site="1" weight="0"/>
-          <arrow x= "1" y="0" z="0" site="2" weight="0"/>
-          <arrow x= "0" y="0" z="0" site="2" weight="1"/>
-          <arrow x="-1" y="0" z="0" site="1" weight="1"/>
+            <arrow site="1" weight="0"><coord axis="x" at="0"/></arrow>
+            <arrow site="2" weight="0"><coord axis="x" at="1"/></arrow>
+            <arrow site="2" weight="1"><coord axis="x" at="0"/></arrow>
+            <arrow site="1" weight="1"><coord axis="x" at="1"/></arrow>
 
       </transition>
 
     </transitions>
 
 </gem-graph-model>
-
diff --git a/schemas/models_0.2.xmls b/schemas/models_0.2.xmls
index 2c8a0a9..f106f88 100644
--- a/schemas/models_0.2.xmls
+++ b/schemas/models_0.2.xmls
@@ -1,9 +1,9 @@
 <?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="node_id" type="xs:integer"/>
+<xs:attribute name="parent" type="xs:integer"/>
 <xs:attribute name="date" type="xs:integer"/>
 <xs:attribute name="name" type="xs:string"/>
 <xs:attribute name="lang" type="xs:string"/>
@@ -11,12 +11,7 @@
 <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:integer"/>
-<xs:attribute name="x" type="xs:integer" default="0"/>
-<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="0"/>
 <xs:attribute name="weight" type="xs:integer" default="0"/>
 
@@ -27,14 +22,6 @@
       <xs:attribute ref="author"/>
 </xs:attributeGroup>
 
-<xs:attributeGroup name="xyz_site_nb">
-      <xs:attribute ref="x"/>
-      <xs:attribute ref="y"/>
-      <xs:attribute ref="z"/>
-      <xs:attribute ref="site"/>
-      <xs:attribute ref="weight"/>
-</xs:attributeGroup>
-
 <xs:element name="g_ref">
     <xs:complexType>
         <xs:simpleContent>
@@ -48,31 +35,38 @@
 
 <xs:element name="quote" substitutionGroup="g_ref"/>
 
-<xs:element name="axis">
+<xs:element name="coord">
     <xs:complexType>
-        <xs:sequence>
-            <xs:element minOccurs="0" ref="quote"/>
-        </xs:sequence>
-        <xs:attribute name="name"  type="xs:string" use="required"/>
-        <xs:attribute name="size"  type="xs:integer" use="required"/>
+        <xs:attribute name="axis" type="xs:string" use="required"/>
+        <xs:attribute name="at" type="xs:integer" use="required"/>
+    </xs:complexType>
+</xs:element>
+
+<xs:element name="dimension">
+    <xs:complexType>
+    <xs:sequence minOccurs="1" maxOccurs="unbounded">
+        <xs:element ref="coord"/>
+    </xs:sequence>
     </xs:complexType>
 </xs:element>
 
 <xs:element name="arrow">
     <xs:complexType>
-        <xs:sequence>
-            <xs:element minOccurs="0" ref="quote"/>
+        <xs:sequence minOccurs="1" maxOccurs="unbounded">
+            <xs:element ref="coord"/>
         </xs:sequence>
-        <xs:attributeGroup ref="xyz_site_nb"/>
+        <xs:attribute name="site" use="required"/>
+        <xs:attribute name="weight" use="required"/>
     </xs:complexType>
 </xs:element>
 
 <xs:element name="condition">
     <xs:complexType>
-        <xs:sequence>
-            <xs:element minOccurs="0" ref="quote"/>
+        <xs:sequence minOccurs="1" maxOccurs="unbounded">
+            <xs:element ref="coord" minOccurs="1" maxOccurs="unbounded"/>
         </xs:sequence>
-        <xs:attributeGroup ref="xyz_site_nb"/>
+        <xs:attribute name="site" use="required"/>
+        <xs:attribute name="weight" use="required"/>
         <xs:attribute ref="node_id" use="required"/>
         <xs:attribute ref="parent" use="required"/>
     </xs:complexType>
@@ -89,16 +83,6 @@
 
 <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="transition">
     <xs:complexType>
         <xs:sequence minOccurs="1" maxOccurs="unbounded">
@@ -113,50 +97,38 @@
 
 <xs:element name="gem-graph-model">
 <xs:complexType>
-<xs:sequence>
+<xs:sequence minOccurs="1" maxOccurs="1">
     <xs:element name="identity">
         <xs:complexType>
-          <xs:sequence>
+          <xs:sequence minOccurs="1" maxOccurs="1">
               <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="g_ref"/>
+              <xs:element ref="g_ref" minOccurs="1" maxOccurs="1"/>
           </xs:sequence>
         </xs:complexType>
     </xs:element>
 
-        <xs:element name="parameters">
+    <xs:element name="parameters">
         <xs:complexType>
-        <xs:sequence>
+        <xs:sequence minOccurs="1" maxOccurs="1">
 
             <xs:element name="simulation">
                 <xs:complexType>
-                <xs:sequence>
-
+                <xs:sequence minOccurs="1" maxOccurs="1">
                     <xs:element name="max_thread" type="xs:integer"/>
-
                     <xs:element name="max_cycles" type="xs:integer"/>
-
                 </xs:sequence>
                 </xs:complexType>
             </xs:element>
 
             <xs:element name="space-param">
                 <xs:complexType>
-                <xs:sequence>
-
-                    <xs:element name="dimension">
-                          <xs:complexType>
-                          <xs:sequence minOccurs="1" maxOccurs="unbounded">
-                                <xs:element ref="axis"/>
-                        </xs:sequence>
-                        </xs:complexType>
-                  </xs:element>
-
+                <xs:sequence minOccurs="1" maxOccurs="1">
+                    <xs:element ref="dimension"/>
                     <xs:element name="site_multiplicity" type="xs:integer"/>
-
               </xs:sequence>
               </xs:complexType>
           </xs:element>
@@ -169,16 +141,16 @@
       <xs:element name="objects">
           <xs:complexType>
           <xs:sequence minOccurs="1" maxOccurs="unbounded">
-              <xs:element ref="state"/>
+              <xs:element ref="object"/>
           </xs:sequence>
           <xs:attributeGroup ref="id_date_author"/>
           </xs:complexType>
       </xs:element>
 
-      <xs:element name="savestates">
+      <xs:element name="savedstates">
           <xs:complexType>
           <xs:sequence minOccurs="0" maxOccurs="unbounded">
-              <xs:element ref="space"/>
+              <xs:element ref="state"/>
           </xs:sequence>
           <xs:attributeGroup ref="id_date_author"/>
           </xs:complexType>