Problems understanding the XMATCH
benjamin.gufler at in.tum.de
Tue Mar 21 06:32:16 PST 2006
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I have some problems understanding the XMATCH which I hope can be solved
with your help.
First of all, there is a little mistake (a forgotten update?) in the
XMATCH section of the ADQL specification (page 6, section 2.2.4):
"The XMATCH has three parameters; first two parameters are table names
to be cross-matched, the third parameter is the sigma value for the
chi-square match, and the final (fourth) parameter, N, represents the
This should imo be: "The XMATCH has *four* parameters;..."
The thing I don't understand is the translation of a XMATCH from ADQL/s
to ADQL/x and back. As described above, XMATCH in ADQL/s has 4
parameters: two tables, the sigma and the cross-matching mode.
The XML schema for ADQL/x defines the corresponding(?) xMatchType as a
sequence of at least two tables (where a table must be either of the
"includeTableType" or the "dropTableType"), a comparison operator and a
My questions are:
1. How can the translation of a crossmatch from ADQL/s to ADQL/x ever
result in a list of more than two tables and where do I get tables
of the dropTableType from?
2. How can a cross-match in ADQL/x containing more than two tables, or
tables of the dropTableType, be translated to ADQL/s?
3. The tables in ADQL/s' XMATCH "function" become <Table../> elements in
ADQL/x, the sigma value is mapped to the <Sigma../> element. How to
translate the cross-matching mode (an integer, as I believe), into a
comparison operator, that is, one of "=", "<>", ">", ">=", "<", "<="?
I appreciate every comment on these questions.
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