Re: [xsl] element in most preferred language expression?

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2008-05-12 17:37 -0700, Jack Bates wrote:
> For the most part, everything we could want from our API can be
> expressed in XPath. One challenge I am facing is multilingual data.
>
> Many of our object's properties may be translated into foreign
> languages. Happily, I think there is an analogue in XML: the xml:lang
> attribute.

And the analogue in XPath:  the lang() function

> The HTTP Accept-Language request header contains a list of the user's
> language preferences and associated weights.
>
> Our API can express the value of a property in a given language. I think
> the corresponding XPath expression would be something
> like: ./title[@xml:lang = "fr"]

I disagree.  That is too literal for xml:lang because if there was a 
property with xml:lang="fr-ca" (Canadian French) and not one with 
xml:lang="fr" (French), then you would inappropriately assume there 
is no French available.

There is also the issue of case ... lang() correctly supports a 
caseless match while your proposal does not.

There is also the issue of ancestry ... an ancestor of the element 
will in fact specify the language of the element when the element 
doesn't have an xml:lang= attribute.

But ... I haven't typically seen lang() used in a predicate and I can 
see an issue.

The XPath expression "title[lang('fr')]" (you don't need the leading 
"./") would return more than one title if the children of the context 
element included:

  <title xml:lang="FR">Bonjour!</title>
  <title xml:lang="fr-ca">Salut!</title>

... but that XPath expression does return the set of matching titles 
without having to do an iteration.

There is no way to weigh either of these as "closer" to 'fr' than the 
other when you use the lang() function.  So you will have to decide 
what to do when more than one item is returned for a given 
language.  If you know your data set won't have such ambiguity, then 
there won't be a problem using lang() as I suggest.

> - the challenge is expressing the value of a property in the most
> preferred language. I can do this in code, by iterating over the user's
> language preferences, getting the property value in each language until
> I get a non-empty node set. However I would like to capture this
> behaviour behind our API. Ideally a developer could express the value of
> a property in the user's most preferred language in a single expression.
> Furthermore, this expression could be combined with other expressions,
> to get for example, the titles of all an object's children, in the
> user's most preferred language.
>
> What is the closest XPath expression which could get the value of an
> element in a most preferred language?

  "title[lang($preferredLanguage)]"

> What advice do you have for how to express this in our API?

Sorry ... no suggestions ... I'm focused on the XPath and how I teach 
the XSLT.  I'll let others comment on the API.

I hope this helps.

. . . . . . . . . . . . Ken

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