SIAP and encoding of POS input parameter
dtody at nrao.edu
Wed Jan 21 10:48:20 PST 2009
XML Schema apparently distinguishes between the lexical representation of
a number, and a "canonical" representation which I quoted below. The
lexical representations of integer and float/double appear to permit a
leading "+", whereas the canonical representations do not.
In any case, the XML Schema Datatypes definition is what we adopted
for SSA/DAL2, mainly because it is defined independently of the
implementation language. This does appear to provide a precise
definition, although it could be clarified in the specifications.
> This kind of thing could be put in an IVOA note or might be worth
> codifying in its own RFC. I don't think this belongs in the individual
> DAL services though. Similar things, like what characters are
> valid in String's? Do we have any support for Unicode in parameters?
> could also be addressed.
There is a draft DAL2 architecture document (DAL service architecture
and stnandard profile) which applies to all the second generation
interfaces, which could be a logical place to put this sort of detail.
Since we are mainly concerned with input parameters here (POS etc.) it
is not sufficient to refer to VOTable or ADQL, although it would be
nice if all of these are consistent. Since VOTable is XML-based I
suspect that DAL2 and VOTable at least are consistent since they both
reference or imply XML Schema datatypes.
On Wed, 21 Jan 2009, Doug Tody wrote:
> And here is the reference:
> An excerpt:
> The canonical representation for float is defined by
> prohibiting certain options from the Lexical representation
> (§22.214.171.124). Specifically, the exponent must be indicated by
> "E". Leading zeroes and the preceding optional "+" sign are
> prohibited in the exponent. If the exponent is zero, it must be
> indicated by "E0". For the mantissa, the preceding optional "+"
> sign is prohibited and the decimal point is required.
> On Wed, 21 Jan 2009, Doug Tody wrote:
>> Hi -
>> Tom's mention of XML schema reminded me of what we actually said about
>> Here is what we have in the SSA spec (intended to apply to all of DAL2):
>> Integer numbers are represented as defined in the specification of
>> integers in XML Schema Datatypes. Real numbers are represented
>> as specified for double precision numbers in XML Schema
>> Datatypes. Sexagesimal formatting is not permitted, either for
>> parameter input or in output metadata, other than in ISO 8601
>> formatted time strings (sexagesimal format is fine for a user
>> interface but inappropriate for a lower level machine interface,
>> where it only complicates things).
>> A basic POS is thus a list of integer or real numbers delimited by
>> commas, with the numbers represented as defined in XML Schema Datatypes.
>> - Doug
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