Format of concatenated UCD's

[Frederic V. "Rick" Hessman]

On 3 Jun 2005, at 10:09 am, Norman Gray wrote:

>
> Frederic,
>
> On 2005 Jun 2 , at 18.24, Frederic V. "Rick" Hessman wrote:
>
>> The point is that the concatenation of UCDs in its present form  
>> (using a
>> semicolon) is effectively an array of UCD strings.  The question is  
>> only
>> which character is defined as the separator.   Since blanks are not  
>> allowed
>> in UCDs, then a blank is as good a separator as a semicolon.  Our
>> argument is that - from an XML perspective - blanks are MUCH BETTER
>> separators, since blanks permit us to check the syntax of a UCD entry
>> in principle whereas a semicolon-separated array of UCD strings looks
>> like a simple string to XML parsers.
>
> UCDs are orthogonal to XML, thus changing the UCD syntax because one  
> particular XML technology allows you to peek inside attribute values  
> (which are opaque in the XML data model), is the tail wagging the dog.
>
> Also, any meaningful checking of UCDs is going to have to do more than  
> split the UCD at semicolons, so having your XML parser API do that for  
> you doesn't seem much of a win.
>
> Blanks would also be a bad intra-UCD separator, since that would stop  
> blanks being the natural inter-UCD separator.  With the semicolon, one  
> can naturally talk of a space-separated list of UCDs, with whatever  
> meaning is appropriate in the context; without it, one cannot.

You're right about having to worry about "intra-" versus "inter-" ;  
will have to think some more :-(

You're wrong about XML attributes being "opaque" or "anonymous": they  
have a clearly defined
base/type.  If you define them as a string, it's because you've chosen  
to make them "opaque" to
the parser, but many attributes aren't strings.    "Opaque" strings are  
good for simple names but not
necessarily good for UCDs.

I would like to also disagree about UCDs and XML being orthogonal: a  
document with a UCD which doesn't
conform to the standard is at best faulty and at worse a sign that it  
has been garbled in transmission,
so you have to check the syntax at some point anyway.  The question is  
whether  you want to be very
forgiving about garbage UCD's (which most XML parsers won't like if  
they get to check the syntax) and
whether you want to maintain 2 parsers instead of 1 (assuming we could  
get XML parsers to do UCDs
as well).

Thanks for the bounce :-)

Rick

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Dr. Frederic V. Hessman      Hessman at Astro.physik.Uni-Goettingen.DE
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