<?xml version="1.0" encoding="UTF-8"?>
<entity_model xmlns="http://www.entitymodelling.org/ERmodel">
<entity_type>
   <name>element</name>
   <presentation>
       <x>0.1</x>
       <y>0.1</y>
   </presentation>
   <value>
      <name>name</name>
      <type>string</type>
	  <identifying/>
   </value>
   <value>
      <name>symbol</name>
      <type>string</type>
   </value>
   <value>
      <name>atomic number</name>
      <type>integer</type>
   </value>
   <value>
      <name>relative atomic mass</name>
      <type>float</type>
   </value>
   <value>
      <name>melting point</name>
      <type>float</type>
   </value>
      <value>
      <name>boiling point</name>
      <type>float</type>
   </value>
      <value>
      <name>density</name>
      <type>float</type>
	  <optional/>
   </value>
   <composition>
       <type>valency</type>
	   <cardinality>OneOrMore</cardinality>
	   <identifying/>
   </composition>
</entity_type>
<entity_type>
   <name>valency</name>
   <presentation>
       <below>element</below>
   </presentation>
   <value>
      <name>number</name>
      <type>integer</type>
	  <identifying/>
   </value>
   </entity_type>
</entity_model>