XML encoding rules

The APDU are defined according to this simplified ASN1 similar document. The protocol-elements are specified as structured types (SEQUENCE, CHOICE, SEQUENCEOF, SEQUENCEOFCHOICE) and simple-types.

The xml-encoding is done according to the following rules:

1. The encoding starts at the the top-level declaration _COSEMpdu which defines the CHOICE of all possible protocol-elements.
   
2. A CHOICE is encoded as an xml-element having the name of the choice member:
   
   <GetRequest>
     <GetRequestNormal>
       ...
     </GetRequestNormal>
   </GetRequest>
   
   
3. A SEQUENCE is encoded as an xml-element containing as many xml-elements as sequence members and whose names are the corresponding member-names. A member marked as OPTIONAL may be omitted:
   
   <AttributeDescriptor>
     <ClassId Value="0008" />
     <InstanceId Value="0000010000FF" />
     <AttributeId Value="02" />
   </AttributeDescriptor>
   
   
4. A SEQUENCEOF is encoded as an xml-element, with a Qty attribute that specifies the number of items. The items are encoded as xml-elements whose names are the type name of the item:
   
   <AttributeDescriptorList Qty="02">
     <_AttributeDescriptorWithSelection>
       ...
     </_AttributeDescriptorWithSelection>
     <AttributeDescriptorWithSelection>
       ...
     </AttributeDescriptorWithSelection>
   <AttributeDescriptorList>
   
   
5. A SEQUENCEOFCHOICE is encoded as an xml-element with a Qty attribute that specifies the number of items. Each item is encoded as an xml-element whose name is the member name of the CHOICE:
   
   <ReadRequest Qty="02">
     <VariableName Value="C008" />
     <ParameterisedAccess>
       ...
     </ParameterizedAccess>
   </ReadRequest>
   
   
6. An ENUMERATED is encoded as an (empty) xml-element with a Value attribute:
   
   <DataAccessError Value="ObjectUnavailable" />
   
   
   
7. All other types are simple types. They are encoded as (empty) xml-elements with a Value attribute encoded as a string of 2 hex-characters per octet:
   
   <DoubleLong Value="01020304" />