CDS.headStuff2
Describing Astronomical Catalogues and Query Results with XML
The present version is dated January 30, 2001.
Participants to the Strasbourg meeting (June 23-25, 1999)
Reference: ``Using XML for Accessing Resources in
Astronomy''
by
F. Ochsenbein1, M. Albrecht2, A. Brighton2, P. Fernique1, D. Guillaume3,
R. Hanisch4, E. Shaya5, A. Wicenec2 2000,
Astronomical Society of the Pacific Conference Series 216,
83
1 CDS, Observatoire Astronomique de Strasbourg, France
2 ESO, Munich, Germany
3 Univ. Illinois, USA
4 STScI, Baltimore, MD, USA
5 GSFC, Greenbelt, MD, USA
We chose to use XML entities (i.e. <tag> ... </tag>) for pieces of data which are normally displayed to the end user, and attributes (i.e. <tag ... name="value" ...>) for specifications which are mostly control information.
Most of the control information is necessary for an automated interpretation for XML front-end tools.
If your browser supports XML, you may try:
<?xml version = "1.0"?>
<!DOCTYPE ASTRO SYSTEM "astrores.dtd">
<ASTRO ID="v0.7">
<DESCRIPTION about="http://astrores.xml.org/ASTRO-Spec-0.2">
See mailing list
</DESCRIPTION>
<!-- DEFINITIONS
a. COOSYS, the system of astronomical coordinates used
b. for photometric system or others..
-->
<DEFINITIONS>
<COOSYS ID="myJ2000"
system="eq_FK5"
equinox="2000."
epoch="2000."/>
</DEFINITIONS>
<!-- The output is made of several tables related together -->
<RESOURCE ID="I/254">
<NAME>GSC1.2</NAME>
<TITLE>The HST Guide Star Catalog, Version 1.2 (Lasker+ 1996)</TITLE>
<DESCRIPTION>
This is an excerpt of the GSC1.2.
This version was re-reduced with PPM catalogue;
see more details about the GSC catalogues at
http://www-gsss.stsci.edu/gsc/gsc.html .
</DESCRIPTION>
<!-- Now comes the definition of each of the individual tables -->
<TABLE ID="gsc_out">
<NAME>gsc.out</NAME>
<TITLE>Output from GSC1.2 Server</TITLE>
<DESCRIPTION>
Default result of GSC1.2 Server around a target
</DESCRIPTION>
<FIELD ID="_r"
ucd="POS_ANG_DIST"
unit="arcmin"
datatype="F"
width="7"
precision="4">
<NAME>_r</NAME>
<DESCRIPTION>Distance from target NGC40</DESCRIPTION>
<VALUES type="actual">
<MIN value="0.0"/>
<MAX value="10.0"/>
</VALUES>
</FIELD>
<FIELD ID="gsc"
datatype="A"
width="10"
ucd="IDENT" >
<NAME>GSC-Id</NAME>
<TITLE>Unique object id</TITLE>
<DESCRIPTION>
The GSC-Id is made of 10 digits, the first 5
representing the place number, and the last 5
the object number on the plate.
</DESCRIPTION>
</FIELD>
<FIELD ID="ra"
ref="#id(myJ2000)"
ucd="POS_EQ_RA"
unit="deg"
datatype="F"
width="9"
precision="5"
format="%RAh %RAm %RAs">
<NAME>RA(J2000)</NAME>
<DESCRIPTION>Right ascension in J2000, epoch of plate</DESCRIPTION>
<VALUES type="actual">
<MIN value="3.0"/>
<MAX value="3.6"/>
</VALUES>
</FIELD>
<FIELD ID="dec"
ref="#id($myJ2000)"
ucd="POS_EQ_DE"
unit="deg"
datatype="F"
width="9"
precision="5"
format="%DEd %DEm %DEs">
<NAME>Dec(J2000)</NAME>
<DESCRIPTION>Declination in J2000, epoch of plate</DESCRIPTION>
</FIELD>
<FIELD ID="pos_err"
unit="arcsec"
datatype="F"
width="4"
precision="1"
ucd="ERROR" >
<NAME>PosErr</NAME>
<DESCRIPTION>Mean error on position</DESCRIPTION>
</FIELD>
<FIELD ID="Pmag"
ucd="PHOT_PHG_MAG"
unit="mag"
datatype="F"
width="5"
precision="2">
<NAME>Pmag</NAME>
<DESCRIPTION>photographic magnitude (see n_Pmag)</DESCRIPTION>
</FIELD>
<FIELD ID="e_Pmag"
ucd="ERROR"
unit="mag"
datatype="F"
width="5"
precision="2">
<NAME>e_Pmag</NAME>
<DESCRIPTION>Mean error on photographic magnitude</DESCRIPTION>
</FIELD>
<FIELD ID="class"
ucd="CLASS_CODE"
datatype="I"
width="1">
<NAME>Class</NAME>
<DESCRIPTION>Class of object (0=star; 3=non-stellar)</DESCRIPTION>
<VALUES type="actual">
<OPTION value="0">star</OPTION>
<OPTION value="3">galaxy</OPTION>
</VALUES>
</FIELD>
<LINK content-role="doc"
title="documentation"
href="http://vizier.cds.unistra.fr/viz-bin/cat/I/254"/>
<LINK content-role="hints"
title="Hints for the display interface"
href="http://vizier.cds.unistra.fr/viz-bin/cat/I/254&-hints"/>
<!-- This section displays the data, in compact CSV form -->
<DATA><CSV colsep="|" headlines="2" ><![CDATA[
_r | GSC-id |RA2000 |DE2000 |Err|Bmag|Err|m
arcmin|----------|deg |deg |arcsrc|mag|mag|
0.0146|0430201297|00 13 00.93|+72 31 19.9|3.6|8.59|0.20|0
0.9704|0430200545|00 12 50.07|+72 30 48.2|0.2|12.18|0.34|0
0.9730|0430200545|00 12 50.04|+72 30 48.1|0.2|12.09|0.20|0
1.5843|0430202363|00 12 44.05|+72 30 22.6|0.2|14.38|0.34|0
2.8586|0430200269|00 12 33.10|+72 29 22.6|0.3|14.96|0.20|3
2.9198|0430200153|00 13 24.64|+72 33 38.3|0.2|12.89|0.20|0
2.9215|0430200153|00 13 24.66|+72 33 38.4|0.2|13.06|0.34|0
3.0487|0430202336|00 12 53.35|+72 34 18.7|0.2|14.38|0.34|0
3.2247|0430200121|00 13 36.48|+72 29 30.2|0.2|12.39|0.21|0
3.2269|0430200121|00 13 36.46|+72 29 29.8|0.2|12.50|0.34|0
]]></CSV></DATA>
</TABLE>
</RESOURCE>
</ASTRO>
<!-- DOCUMENT TYPE DEFINITION FOR THE ASTRONOMICAL RESOURCES
Version 0.9 - 17-Apr-2000 == ID / IDREF definitions
Version 0.8 - 16 Janv 2000 == LINK Modifications
Version 0.7 - 20 Dece 1999 == Allan Brighton's Remarks
Version 0.6 - 06 Nove 1999 == Addition of <CSV> tag
Version 0.5 - 24 Sept 1999
Version 0.4 - 28 july 1999
Version 0.3 - 25 july 1999
Version 0.2 - 12 july 1999
Version 0.1 - 29 june 1999
This DTD describes the architecture of XML documents
for astronomical resources. Astronomical resources means
in this context:
. excerpt tables or complete tables
. lists of table descriptions
. lists of server descriptions
The aim is to give enough knowledge to the user interfaces
to manipulate these resources (units, formats, anchors, natural
language descriptions, nomenclatures, value ranges...).
Syntax policy
=============
- The element names are in uppercase in order to help the reading.
- The attribute names are preferably in lowercase (exception
for ID from the Xpointer standard)
- The attribute values are not set directly in the DTD but indicated
in comments to facilitate the reading and future extensions.
Remarks about the ID attribute
==============================
This DTD use the ID attribute defined by Xpointer standard
in order to refer the elements between them:
The attribute ID can take any authorized values in XML.
Each ID MUST BE UNIQUE in the XML document.
To refer to an element the Xpointer standard is used. For
example attr="myJ2000" refers to the element that contains ID="myJ2000"
in the current XML document. An alternative to this notation has
been introduced with the classical $NAME variable (or ${NAME}). This
notation will be prefered in case of substitutions (URL template,
epochs depending of the row values,...
ex: http://vizier.cds.unistra.fr/viz-bin?-c=$ra+$de&-r=10)
Remarks about DATA element
==========================
The DATA element can indicate different structures depending
of the origin and the size of the DATA.
-> CSV embedded (Character Separated values)
-> Full XML tagging
-> anchor to external data
In case of CSV syntax, headings are authorized to help the reading.
The LINK element has been defined to set together any
URL template for queries, documentation, additional
information... It follows the Xlink syntax.
This attribute does not work with IE...
xmlns:ASTRO CDATA #IMPLIED
-->
<!ELEMENT ASTRO (DESCRIPTION?, DEFINITIONS?, INFO*, RESOURCE+) >
<!ATTLIST ASTRO
ID ID #IMPLIED
>
<!ELEMENT RESOURCE (DEFINITIONS*, NAME?, TITLE?, DESCRIPTION?, INFO*,
FIELD*, TABLE*, LINK* ) >
<!ATTLIST RESOURCE
ID ID #IMPLIED
type (results|meta) "results" >
<!-- Details of the used parameters -->
<!ELEMENT INFO (#PCDATA)>
<!-- ID To refer this element
name Argument's canonical name (ASU);
when absent, the argument can't be used for back queries.
value Argument's contents
-->
<!ATTLIST INFO
ID ID #IMPLIED
name CDATA #IMPLIED
value CDATA #IMPLIED >
<!-- To specify ranges or lists of values
In case of use in <FIELD> tag, the type attribute
can be used to indicate the kind of values.
The multiple attribute specifies that it is
not an exclusive list of value, and in this case
the separator value indicates the character to
separate several values
type legal|actual
multiple yes|no
separator a letter, by default "," -->
<!-- Astronomical table -->
<!-- Note: table may be empty .. thus ================ FIELD* -->
<!ELEMENT TABLE (NAME?, TITLE?, DESCRIPTION?, COOSYS*, FIELD*, LINK*, DATA?) >
<!ATTLIST TABLE
ID ID #IMPLIED >
<!-- 1) In TABLE tag: Catalog or table shortname
ex: "GSC1.2"
2) In FIELD tag: field name
ex: "RA(J2000)" -->
<!ELEMENT NAME (#PCDATA) >
<!-- 1) In TABLE tag: Catalog or table description (paragraph)
ex: "This is an excerpt of the GSC1.2. This version was re-reduced
with PPM catalogue; see more details about..."
2) In FIELD tag: field description (paragraph) -->
<!ELEMENT DESCRIPTION (#PCDATA) >
<!ATTLIST DESCRIPTION
about CDATA #IMPLIED >
<!-- 1) In TABLE tag: Catalog or table title in one line
ex: "The HST Guide Star Catalog, Version 1.2 (Lasker+ 1996)"
2) In FIELD tag: field description (paragraph)
ex: "Right ascension in J2000, epoch of plate" -->
<!ELEMENT TITLE (#PCDATA) >
<!-- Definition of a field -->
<!ELEMENT FIELD (NAME?, TITLE?, DESCRIPTION?, VALUES*, LINK? ) >
<!-- ID To refer this element
unit Unit used for the field (see appendix)
datatype Datatype of field value
F-float, D-double, I-integer, A-ascii
L-boolean (logical), E-exponential
precision Precision of field value: number of significant digits
after the dot (ex: "3")
width number of characters "8"
format indicate the format by a "%fmt" template (as "printf()"
in language C). Use for coordinate format, time and date
formats (ex: "%RAh:%RAmd %DEd:%DEmd" - (see appendix)
ref Reference to the system for this field. For example it can be
a coordinate or a photometric system.
ex : #id("myJ2000") -> The syntax comes from Xpointers
name Alternative to specify the name of the field if it uses
only ascii characters (see the NAME element for the
other possibility)
ucd Unified column descriptor "POS_EQ_RA" (ESO/CDS work)
type To characterize the field
hidden for fields used typically for server/client exchange
no_query for fields which specify some parameters
(e.g. the equinox of a coordinate system)
trigger for fields which contain a parameter for an action
actualvalues Reference to the range or list of actual values
(it is an alternative to the <VALUES> entity in order to
be able to factorize them)
legalvalues Reference to the range or list of legal values
(it's an alternative to the <VALUES> entity in order to
be able to factorize them)
-->
<!ATTLIST FIELD
ID ID #IMPLIED
unit CDATA #IMPLIED
datatype (F|I|D|E|A|L) #IMPLIED
precision CDATA #IMPLIED
width CDATA #IMPLIED
format CDATA #IMPLIED
ref IDREF #IMPLIED
name CDATA #IMPLIED
ucd CDATA #IMPLIED
type (hidden|no_query|trigger) #IMPLIED >
<!-- To specify ranges or lists of values
In case of use in <FIELD> tag, the type attribute
can be used to indicate the kind of values.
The multiple attribute specifies that it is
not an exclusive list of value, and in this case
the separator value indicates the character to
separate several values
type legal|actual
multiple yes|no
separator a letter, by default "," -->
<!ELEMENT VALUES (MIN*, MAX*, OPTION*, NULL?) >
<!ATTLIST VALUES
ID ID #IMPLIED
multiple (yes |no) "no"
type (legal|actual) "legal" >
<!-- Min of a value range
value the min
inclusive yes|no (default: yes) -->
<!ELEMENT MIN (#PCDATA) >
<!ATTLIST MIN
value CDATA #REQUIRED
inclusive (yes |no) "yes" >
<!-- Max of a value range
value the max
inclusive yes|no (default: yes) -->
<!ELEMENT MAX (#PCDATA) >
<!ATTLIST MAX
value CDATA #REQUIRED
inclusive (yes |no) "yes" >
<!-- Item of list of values. The content of the
OPTION tag can be not empty to indicate
a corresponding sentence (ex: value="I/239"
and content: "Hipparcos catalog"
NOTE: OPTION may include VALUE for hierarchical menus.
(therefore OPTION can't have #PCDATA)
-->
<!ELEMENT OPTION (OPTION*) >
<!ATTLIST OPTION
name CDATA #IMPLIED
value CDATA #REQUIRED >
<!-- Specify the value for the null representation
value the null representation -->
<!ELEMENT NULL (#PCDATA) >
<!ATTLIST NULL
value CDATA #REQUIRED >
<!-- Link to relevant information.
The LINK indicates a possibility to retrieve more data,
in a mime type specified in the content-type attribute,
for a purpose sketched in the content-role attribute;
the title attribute is the text which can be proposed
for e.g. a header of a button label,
and the value attribute can propose a text for each
row (using the substitution possibilities)
The link can be defined in one of the 3 forms:
1. Via the href (e.g.. href="http://...?param=${id-field}..." ),
2. Via the action (e.g.. action="http://...")
which acts as the html FORM tag:
the full link is the concatenation of:
-> the action contents
-> each field of the <RESOURCE> with no type or marked as type="hidden"
is appended as ${name}=${value}
where ${name} stands for the contents of the name attribute
of in the FIELD tag
${value} stands for the relevant value
3. Via the gref (the GLU way of specifying the link)
The link may contain $ symbols indicating variable substitution,
(see "Remarks about the ID attribute" above)
The purpose of the link defined by the content-role attribute may
contain the following keys:
query URL template to query the resource
hints URL template to get additional information proposed
by the server for use by the application
doc URL template to get documentation about the resource
.... (other tbd's) -->
<!ELEMENT LINK (#PCDATA) >
<!ATTLIST LINK
ID ID #IMPLIED
content-role (query|hints|doc) #IMPLIED
content-type CDATA #IMPLIED
title CDATA #IMPLIED
value CDATA #IMPLIED
href CDATA #IMPLIED
gref CDATA #IMPLIED
action CDATA #IMPLIED >
<!-- Data of the table. The data may be supplied via a link,
as Character-Separed-Values (CSV) or
as a fully-tagged XML table (TABLEDATA).
For CSV data, the possible attributes are
colsep column separator (by default \t) (ex: "|")
recsep record separator (by default \n) (ex: "\r")
headlines number of heading lines to ignore (comment lines)
For TABLEDATA, made of rows, each row made of cells
Empty tables (no row) are allowed;
but a row cannot be made of zero cell.
-->
<!ELEMENT TABLEDATA (ROW*)>
<!ATTLIST TABLEDATA
headlines CDATA #IMPLIED >
<!ELEMENT ROW (CELL+) >
<!ELEMENT CELL (#PCDATA)>
<!ATTLIST CELL
ref IDREF #IMPLIED >
<!ELEMENT DATA (TABLEDATA | LINK | CSV) >
<!ELEMENT CSV (#PCDATA)>
<!ATTLIST CSV
recsep CDATA #IMPLIED
colsep CDATA #IMPLIED
headlines CDATA #IMPLIED >
<!-- General definitions for default system coordinates and
set of values -->
<!ELEMENT DEFINITIONS (COOSYS*) >
<!-- Coordinate system declaration -->
<!ELEMENT COOSYS (#PCDATA) >
<!-- ID to refer it "myJ2000"
system eq_FK4|eq_FK5|ICRS|ecl_FK4|ecl_FK5|
galactic|supergalactic|xy|barycentric|geo_app
equinox the equinox
epoch the epoch
x Alternative for referring to RA
y Alternative for referring to DE
-->
<!ATTLIST COOSYS
ID ID #IMPLIED
system (eq_FK4|eq_FK5|ICRS|ecl_FK4|ecl_FK5|galactic|supergalactic|xy|barycentric|geo_app) "eq_FK5"
equinox CDATA #IMPLIED
epoch CDATA #IMPLIED
x CDATA #IMPLIED
y CDATA #IMPLIED >
<!-- APPENDIX
"unit" attibute values (FIELD element)
______________________________________
% percent 10-2
A Ampere A
a year 3.15576x10+7s
al light-year 9.46053x10+15m
Angstroem Angstroem (0.1nm) 10-10m
arcmin minute of arc 4.62963x10-5
arcsec second of arc 7.71605x10-7
atm atmosphere 1.01325x10+5Pa (kg.m-1.s-2)
AU astronomical unit 1.49598x10+11m
au astronomical unit 1.49598x10+11m
bar ?bar(10+5Pa) 10+5Pa (kg.m-1.s-2)
barn barn(10-28m2) 10-28m+2
bit binary information unit
byte byte(8bits)
C Coulomb C (s.A)
c c(speed_of_light) 2.99792x10+8m.s-1
cal calorie 4.1854J (kg.m+2.s-2)
cd candela(lumen/sr) cd
ct count
D Debye (dipole) 3.33333x10-30m.s.A
d day 8.64x10+4s
deg degree 2.77778x10-3
dyn dyne(10-5N) 10-5N (kg.m.s-2)
e e(electron_charge) 1.60218x10-19C (s.A)
erg erg(10-7J) 10-7J (kg.m+2.s-2)
eV electron-Volt 1.60218x10-19J (kg.m+2.s-2)
F Farad F (kg-1.m-2.s+4.A+2)
G G(gravitation) 6.67x10-11kg-1.m+3.s-2
g gram 10-3kg
gauss Gauss(10-4T) 10-4T (kg.s-2.A-1)
H Henry H (kg.m+2.s-2.A-2)
h hour 3.6x10+3s
hr hour(use 'h') 3.6x10+3s
Hz Herz Hz (s-1)
inch inch 2.54x10-2m
J Joule J (kg.m+2.s-2)
JD Julian Day 8.64x10+4s
Jy Jansky(10-26W/m2/Hz) 10-26kg.s-2
K Kelvin K
k k(Boltzmann) 1.38062x10-23kg.m+2.s-2.K-1
kg kilogram kg
l litre 10-3m+3
lm lumen 7.95775x10-2cd
lx lux(lm/m2) 7.95775x10-2m-2.cd
lyr light-year (c*yr) 9.46053x10+15m
m metre m
mag magnitude mag
mas milli-second of arc 7.71605x10-10
me electron_mass 9.10956x10-31kg
min minute 6x10+1s
MJD Mod. JD (JD-2400000.5) 8.64x10+4s
mmHg mercury_mm 1.33322x10+2Pa (kg.m-1.s-2)
mol mole mol
month month
mp proton_mass 1.67266x10-27kg
N Newton N (kg.m.s-2)
Ohm Ohm(V/A) Ohm (kg.m+2.s-3.A-2)
Pa Pascal Pa (kg.m-1.s-2)
pc parsec 3.0857x10+16m
ph photon
pi pi(=3.14...) 3.14159
pix pixel
R R(gas_constant) 8.3143kg.m+2.s-2.K-1.mol-1
rad radian 1.59155x10-1
Ry Rydberg(13.6eV) 2.17989x10-18J (kg.m+2.s-2)
S Siemens(A/V) S (kg-1.m-2.s+3.A+2)
s second s
sec second (use 's') s
solLum solar luminosity 3.826x10+26W (kg.m+2.s-3)
solMass solar mass 1.989x10+30kg
solRad solar radius 6.9599x10+8m
sr steradian 7.95775x10-2
Sun Solar unit
T Tesla T (kg.s-2.A-1)
t ton 10+3kg
V Volt V (kg.m+2.s-3.A-1)
W Watt W (kg.m+2.s-3)
Wb Weber(V.s) Wb (kg.m+2.s-2.A-1)
yr year 3.15576x10+7s
"format" attibute value (FIELD element)
______________________________________
COOd entire coord. string in decimal degrees (76.96583 -76.44222)
COO entire coord. string in sex. format (05 07 51.8 -76 26 32)
RA RA in standard sexagesimal form (05 07 51.8)
RAdeg RA in degrees (76.96583)
RAh hours of right ascension (05)
RAhd RA in decimal hours (5.13106)
RAm minutes of RA (07)
RAmd minutes of RA including any fractional minutes (07.9)
RAs seconds of RA (52)
RAsd seconds of RA including fractional seconds (51.8)
DE DE in standard sexagesimal form (-76 26 32.0)
DEdeg DE in degrees (-76.44222)
DEd degrees of DE (-76)
DEm minutes of DE (26)
DEmd minutes of DE including fractional minutes (26.5)
DEs seconds of DE (32)
DEsd seconds of DE including fractional seconds (32.0)
LON longitudinal coord. in degrees (288.48372)
LAT latitudinal coord. in degrees (-32.30250)
-->
<!-- APPENDIX
"time" formats (Astrobrowse and GLU Definitions)
See http://heasarc.gsfc.nasa.gov/ab/time.html
("UTC", "TAI", or "other")
Symbol Meaning Example
====================================================
YYYY 4-digit year 1999
YYYYffff 4-digit year with fractional year 1999.0877
YY 2-digit year 99
DDD 3-digit day of year 032
DDDffffff 3-digit day of year with 6-digit 032.218142
fractional day
MM 2-digit month 02
DD 2-digit day of month 01
DDfff 2-digit day of month with 3-digit 01.218
fractional day
hh 2-digit hour of day 05
mm 2-digit minute of hour 14
ss 2-digit seconds of minute 07
ssff seconds of minute with fraction 07.45
hhffff hours with decimal fraction 05.1242
month name of month in lowercase february
Month name of month (capitalized) February
mon abbrev name of month feb
JD Julian Date 2451210.71814178
TJD Truncated Julian Date 11210.2181417824
MJD Modified Julian Date 51210.2181417824
SHF SHF: short history file time key 602313260
XTE XTE mission day with fractional 1857.21818287037
day
-->
<?xml version="1.0" ?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"
xmlns:HTML="http://www.w3.org/Profiles/XHTML-transitional">
<xsl:template><xsl:apply-templates/></xsl:template>
<xsl:template match="text()"><xsl:value-of/></xsl:template>
<xsl:template match="/">
<HTML>
<HEAD>
<TITLE><xsl:value-of select="ASTRO/RESOURCE/NAME"/></TITLE>
</HEAD>
<BODY>
<H1><xsl:value-of select="ASTRO/RESOURCE/TITLE"/></H1>
<I><xsl:value-of select="ASTRO/RESOURCE/DESCRIPTION"/></I>
<HR/>
<xsl:for-each select="ASTRO/RESOURCE/TABLE">
<H2><xsl:value-of select="TITLE"/></H2>
<H3>Column description:</H3><UL>
<xsl:for-each select="FIELD">
<LI>
<xsl:value-of select="NAME"/>: <xsl:value-of select="TITLE"/> <I><xsl:value-of select="DESCRIPTION"/></I></LI>
</xsl:for-each>
</UL>
<H2>Data:</H2>
<PRE><xsl:value-of select="DATA/CSV"/></PRE>
</xsl:for-each>
<HR/>
</BODY>
</HTML>
</xsl:template>
</xsl:stylesheet>
Version 16 July 1999
The default VizieR Query brings up a description of the various usable parameters.