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Is the DLMS .xsd file correct?

From: Steve Underwood <steveu@coppice.org>
Date: Wed, 8 Jun 2016 19:02:14 +0800
To: xmlschema-dev@w3.org
Message-ID: <e4390edd-1726-a19b-d661-2e36ca42c0a1@coppice.org>

DLMS is a communications protocol for Smart Grid applications. At 
there is an XSD file for the XML representation of DLMS. In this file 
can be found the following snippet:

     <xsd:elementname="dedicated-key" minOccurs="0" type="xsd:hexBinary"/>
     <xsd:elementname="response-allowed" default="true" 
     <xsd:elementname="proposed-quality-of-service" minOccurs="0" 
     <xsd:elementname="proposed-dlms-version-number" type="Unsigned8"/>
     <xsd:elementname="proposed-conformance" type="Conformance"/>
     <xsd:elementname="client-max-receive-pdu-size" type="Unsigned16"/>

By the DLMS protocol definition, the first 3 items in that sequence 
should be optional. The minOccurs="0" elements cause items 1 and 3 to be 
correctly treated as optional. However, with the parsers I have tried 
(e.g. libxml2) the second item is handled as a required element. From 
reading the XSD spec it seems that second item should contain 
minOccurs="0", because that is the only way to make items optional. I 
suspect someone has incorrectly assumed that default="true" makes the 
item optional, but I see nothing in the XSD spec to support that.

Can any XSD expert comment on this?

Received on Wednesday, 8 June 2016 13:12:46 UTC

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