Update index.bs

Author: GabrielaRubioDomingo

specs/index.bs

@@ -999,6 +999,11 @@ The Data Type <{HOC}> contains [=HOC=] data. It is referenced in a [=Transport C
         <td>String
         <td>M
         <td>The id of the <{HOC}>
+      <tr>
+        <td><dfn>hubType</dfn>
+        <td>String
+        <td>M
+        <td>The id of the <{HOC}>
   </table>
   <figcaption>Properties of data type `HOC`</figcaption>
 </figure>
@@ -1273,10 +1278,34 @@ It MUST be encoded as a String using one of the following values:
 :: for transport mode `inland waterway`
 
 : <dfn>Hub</dfn>
-:: for hub operations
+:: for hub operations ISSUE: Hub operations should maybe be excluded from here, as these transport modes are defined for TOC, and HOC is defined separately
 
 </dl>
 
+### Data Type <dfn enum>HubType</dfn> ### {#dt-transport-mode}
+
+The Data Type {{HubType}} is an enumeration of the main hub types as defined in the [[!GLEC]] Framework.
+
+It MUST be encoded as a String using one of the following values:
+
+<dl dfn-type="enum-value" dfn-for="HubType">
+
+: <dfn>Transshipment</dfn>
+:: for transport mode `road`
+
+: <dfn>StorageAndTransshipment</dfn>
+:: for transport mode `rail`
+
+: <dfn>Warehouse</dfn>
+:: for transport mode `air`
+
+: <dfn>LiquidBulkTerminal</dfn>
+:: for transport mode `sea`
+
+: <dfn>MaritimeContainerTerminal</dfn>
+:: for transport mode `inland waterway`
+
+</dl>
 
 ### Data Type <dfn>Decimal</dfn> ### {#dt-decimal}