diff --git a/internal-dev/cheminf-ext.owl b/internal-dev/cheminf-ext.owl
index bc0c161c..f8e51dae 100644
--- a/internal-dev/cheminf-ext.owl
+++ b/internal-dev/cheminf-ext.owl
@@ -54,7 +54,7 @@
 
     <owl:Class rdf:about="http://purl.enanomapper.org/onto/ENM_8000030">
         <rdfs:subClassOf rdf:resource="http://semanticscience.org/resource/CHEMINF_000123"/>
-        <rdfs:isDefinedBy>Descriptors that have been obtained through modelling.</rdfs:isDefinedBy>
+        <obo:IAO_0000115>Descriptors that have been obtained through modelling.</obo:IAO_0000115>
         <rdfs:label xml:lang="en">predicted descriptors</rdfs:label>
     </owl:Class>
     
@@ -62,7 +62,7 @@
 
     <owl:Class rdf:about="http://purl.enanomapper.org/onto/ENM_8000031">
         <rdfs:subClassOf rdf:resource="http://semanticscience.org/resource/CHEMINF_000123"/>
-        <rdfs:isDefinedBy>Descriptors that have been obtained through modelling.</rdfs:isDefinedBy>
+        <obo:IAO_0000115>Descriptors that have been obtained through modelling.</obo:IAO_0000115>
         <rdfs:label xml:lang="en">calculated descriptors</rdfs:label>
     </owl:Class>
     
@@ -70,7 +70,7 @@
 
     <owl:Class rdf:about="http://purl.enanomapper.org/onto/ENM_8000032">
         <rdfs:subClassOf rdf:resource="http://semanticscience.org/resource/CHEMINF_000123"/>
-        <rdfs:isDefinedBy>A class of descriptors derived using CDK, the Chemistry Development Kit.</rdfs:isDefinedBy>
+        <obo:IAO_0000115>A class of descriptors derived using CDK, the Chemistry Development Kit.</obo:IAO_0000115>
         <rdfs:label xml:lang="en">cdk descriptors</rdfs:label>
     </owl:Class>
     
@@ -78,7 +78,7 @@
 
     <owl:Class rdf:about="http://purl.enanomapper.org/onto/ENM_1200002">
         <rdfs:subClassOf rdf:resource="http://semanticscience.org/resource/CHEMINF_000464"/>
-        <rdfs:isDefinedBy>PMCID is a unique identifier for publications archived in PubMed Central, which may also be indexed in PubMed. </rdfs:isDefinedBy>
+        <obo:IAO_0000115>PMCID is a unique identifier for publications archived in PubMed Central, which may also be indexed in PubMed. </obo:IAO_0000115>
         <rdfs:label xml:lang="en">PubMedCentral Identifier (PMCID)</rdfs:label>
     </owl:Class>
 
@@ -86,7 +86,7 @@
 
     <owl:Class rdf:about="http://purl.enanomapper.org/onto/ENM_1200003">
         <rdfs:subClassOf rdf:resource="http://semanticscience.org/resource/CHEMINF_000102"/>
-        <rdfs:isDefinedBy>A crystal structure following the formula ABX3</rdfs:isDefinedBy>
+        <obo:IAO_0000115>A crystal structure following the formula ABX3</obo:IAO_0000115>
         <rdfs:label xml:lang="en">perovskite</rdfs:label>
     </owl:Class>
 
@@ -94,10 +94,18 @@
 
     <owl:Class rdf:about="http://purl.enanomapper.net/onto/ENM_8461735">
         <rdfs:subClassOf rdf:resource="http://purl.obolibrary.org/obo/BFO_0000019"/>
-        <rdfs:isDefinedBy>Increased energy price of a reaction due to steric effects (the atomic spacial arrangement in a molecule or ion)</rdfs:isDefinedBy>
+        <obo:IAO_0000115>Increased energy price of a reaction due to steric effects (the atomic spacial arrangement in a molecule or ion)</obo:IAO_0000115>
         <rdfs:label xml:lang="en">Steric hindrance</rdfs:label>
     </owl:Class>
 
+    <!-- http://purl.enanomapper.net/onto/ENM_6390284 -->
+
+    <owl:Class rdf:about="http://purl.enanomapper.net/onto/ENM_6390284">
+        <rdfs:subClassOf rdf:resource="http://semanticscience.org/resource/CHEMINF_000101"/>
+        <obo:IAO_0000115>Point defects in the bulk or surface of a material</obo:IAO_0000115>
+        <rdfs:label xml:lang="en">Oxygen vacancies</rdfs:label>
+    </owl:Class>
+
 </rdf:RDF>