Standard way to represent null attribute values in XML? [duplicate]

Question

Possible Duplicate:
What is the correct way to represent null XML elements?

Is there a standard way to represent null attribute values in XML?

We have an existing XML format that expects fragments similar to:

<items>
  <item key="key_goes_here" value="value_goes_here" />
  ...
</items>

The original format didn't anticipate the need to distinguish between a null value and an empty string value -- however, that is important (now).

My gut says to create a new format that avoids attributes for nullable values, and use elements for them instead:

<items>
  <item key="key_goes_here_and_is_never_null">
    <value xsi:nil="true" /> 
  </item>
</items>

That said, I'd rather keep attributes if there's a standard way to represent null attribute values in XML.

Answer 1

I don't know about any standard, but how about using

<item key="key" />

for items that don't have a value,

<item key="key">
    <value /> 
</item>

for items that have an empty string as a value and

<item key="key">
    <value>This is the value</value> 
</item>

for items that actually have a value?