diff --git a/SDT/schema4.0/docs/SDT_Components.md b/SDT/schema4.0/docs/SDT_Components.md
index 5162873528e54afe87b2c2f6cbfaf8b0894ecf3e..2a629f4b5161b0ba4c177e6f53bc1ef31fe7e4eb 100644
--- a/SDT/schema4.0/docs/SDT_Components.md
+++ b/SDT/schema4.0/docs/SDT_Components.md
@@ -116,7 +116,6 @@ Typical *ModuleClasses* might be equivalent to "power ON/OFF", "Open/Close", "Pa
 
 #### Attributes
 - **name** : Name of the *ModuleClass*. The name must be unique in the scope of the [Domain](#Domain). Required.
-- **optional**: Boolean that indicates whether a *ModuleClass* is optional or mandatory. Optional, the default is *false*.
 - **semanticURI** : An attribute that contains a URI to a semantic description of the element. Optional.
 - **minOccurs** : An optional string attribute that indicates the minimum cardinality of a *ModuleClass*, for example, in a [DeviceClass](#DeviceClass) definition. Optional. The default is "1".  
 Note, if only the *minOccurs* attribute is specified, it can't be greater than 1, because the default value for *maxOccurs* is 1.