[sc34wg3] Null in the data model

[Patrick Durusau]

Greetings,

A couple of questions about "null" in the latest draft of the data model:

Wording:

>    Null is used to indicate that properties have no value; 
> it does not necessarily indicate that the value of the property 
> is unknown. In this model null can never be contained in a set.
> 

Not really sure what it means to indicate that a property has no value 
but at the same time it may be known? Seems to me that if it has no 
value, by definition the value cannot be known.

Or is this an allusion to possible processing that might make the 
property known? Seems like at any point the value is either known or not?

XML Infoset:

The XML infoset deliberately avoids the use of "null" in favor of 
"unknown" and "no value." 
(http://www.w3.org/TR/2001/REC-xml-infoset-20011024/, see 1 
Introduction, under heading "'Unknown' and 'No Value'")

> Some properties may sometimes have the value unknown or no value, 
> and it is said that a property value is unknown or that a property 
> has no value respectively. These values are distinct from each other 
> and from all other values. In particular they are distinct from the 
> empty string, the empty set, and the empty list, each of which simply 
> has no members. This specification does not use the term null since 
> in some communities it has particular connotations which may not match 
> those intended here. 

If we are going to rely upon the XML Infoset, shouldn't we be following 
its practice of "no value" rather than the more problematic "null?"

(Not that I am conceding that the XML Infoset is appropriate outside of 
XTM but if a majority of the committee wants to follow it, I am 
concerned that we actually do what we say we are doing.)

Hope everyone is having a great day!

Patrick

-- 
Patrick Durusau
Director of Research and Development
Society of Biblical Literature
Patrick.Durusau@sbl-site.org
Chair, V1 - Text Processing: Office and Publishing Systems Interface
Co-Editor, ISO 13250, Topic Maps -- Reference Model

Topic Maps: Human, not artificial, intelligence at work!