diff --git a/examples/embedded/uberon-external.sssom.tsv b/examples/embedded/uberon-external.sssom.tsv
new file mode 100644
index 00000000..07e7abff
--- /dev/null
+++ b/examples/embedded/uberon-external.sssom.tsv
@@ -0,0 +1,20 @@
+# curie_map:
+#   FBbt: http://purl.obolibrary.org/obo/FBbt_
+#   UBERON: http://purl.obolibrary.org/obo/UBERON_
+#   ZFA: http://purl.obolibrary.org/obo/ZFA_
+#   MYINTERNALNAMESPACE: http://my.internal.ns/vocab/
+#   semapv: https://w3id.org/semapv/
+#   skos: http://www.w3.org/2004/02/skos/core#
+#   dc: http://purl.org/dc/terms/
+# license: https://w3id.org/sssom/license/unspecified
+# mapping_set_id: https://w3id.org/sssom/mappings/12345287613876278135
+# extension_definition:
+#   - key: modified
+#     value: dc:modified
+#   - key: mapping_id
+#     value: MYINTERNALNAMESPACE:mapping_id
+#   - key: funded_by
+#     value: foaf:fundedBy
+subject_id	predicate_id	object_id	mapping_justification	modified	mapping_id	funded_by
+UBERON:0000004	skos:exactMatch	ZFA:0000047	semapv:UnspecifiedMatching	2022-03-01	M6972619762	NIH:RM1-HG010860-01
+UBERON:0000005	skos:exactMatch	FBbt:00005157	semapv:UnspecifiedMatching	2022-02-01	M98879876121	NIH:RM1-HG010860-01
\ No newline at end of file
diff --git a/src/sssom_schema/schema/sssom_schema.yaml b/src/sssom_schema/schema/sssom_schema.yaml
index 86ff1226..b2c3b2f3 100644
--- a/src/sssom_schema/schema/sssom_schema.yaml
+++ b/src/sssom_schema/schema/sssom_schema.yaml
@@ -456,15 +456,38 @@ slots:
     slot_uri: rdfs:seeAlso
     range: string
     multivalued: true
+  extension:
+    description: A way to extend SSSOM mapping fields with your use case specific information. 
+      Any extension must be declaced in the extension_definition element on mapping_set level.
+      Extensions MUST NOT alter the semantics of the mapping, as they will be disregarded by most standard tools,
+      i.e. not included as part of API requests and others.
+    range: key value pair
+    multivalued: true
+  extension_definition:
+    description: A way to extend SSSOM mapping fields with your use case specific information. 
+    # can I make the 'value' slot of type resource for this element, but otherwise re-use the generic key-value pair class?
+    # Or better keep that element optional and simply tread extensions as package that is ignored by transformers?
+    range: key value pair
+    multivalued: true
   other:
-    description: Pipe separated list of key value pairs for properties not part of
-      the SSSOM spec. Can be used to encode additional provenance data.
+    description: An open ended field in which any information can be added that can be captured as a string. It is recommended 
+      to avoid using this field in favour of the 'comment' or 'extenion fields.
     range: string
   comment:
     description: Free text field containing either curator notes or text generated
       by tool providing additional informative information.
     slot_uri: rdfs:comment
     range: string
+  key:
+    description: Generic slot for key, which should correspond to a entity reference
+    range: string
+    # Any more restrictions, like alphabetical?
+    examples:
+      - value: mapping_id
+      - value: audience
+  value:
+    description: Generic slot for a value with no restrictions
+    range: string
 classes:
   mapping set:
     description: Represents a set of mappings
@@ -497,6 +520,8 @@ classes:
     - see_also
     - other
     - comment
+    - extension
+    - extension_definition
   mapping:
     description: Represents an individual mapping between a pair of entities
     slots:
@@ -540,6 +565,7 @@ classes:
     - see_also
     - other
     - comment
+    - extension
     class_uri: owl:Axiom
   mapping registry:
     description: A registry for managing mapping sets. It holds a set of 
@@ -563,3 +589,8 @@ classes:
       - mapping_set_group
       - last_updated
       - local_name
+  key value pair:
+    description: A simple structure to hold key-value pairs
+    slots:
+      - key
+      - value
\ No newline at end of file