tapquery can query remote databases using the Table Access
Protocol (TAP) services by submitting Astronomical Data Query Language
queries to them and retrieving the results. TAP and ADQL are Virtual
Observatory protocols.
Queries can be submitted in either synchronous or asynchronous
mode, as determined by the sync parameter. In asynchronous mode, if
the query has not been deleted by the time the command exits (see the
delete parameter), the result can be picked up at a later stage using
the tapresume command. Table uploads are supported, so it is possible
(if the service supports this functionality), to upload a local table to the
remote database, perform a query involving it, such as a join with a remote
table of some sort, and receive the result. This powerful facility gives you
crossmatches between local and remote tables.
This command does not provide any facility for querying the
service for either table or capability metadata, so you will need to know
about the service capabilities and database structure from some other source
(possibly TOPCAT).
Note: this command has been introduced at STILTS version
2.3, at which time most available TAP services are quite new and may not
fully conform to the standards, and usage patterns are still settling down.
For this reason you may find that some TAP services do not behave quite as
expected; it is also possible that in future versions the command behaviour
or parameters will change in line with changing service profiles or in the
light of user experience.
- nupload=<count>
The number of upload tables for this task. For each of
the upload tables N there will be associated parameters
ufmtN,
uploadN and
ucmdN.
- ufmtN=<in-format>
Specifies the format of upload table #N as specified by
parameter
uploadN. The known formats are listed in SUN/256. This flag
can be used if you know what format your table is in. If it has the special
value
(auto) (the default), then an attempt will be made to detect the
format of the table automatically. This cannot always be done correctly
however, in which case the program will exit with an error explaining which
formats were attempted. This parameter is ignored for scheme-specified tables.
- uploadN=<tableN>
The location of upload table #N. This may take one of the
following forms:
- A filename.
- A URL.
- The special value "-", meaning standard input. In this
case the input format must be given explicitly using the ufmtN
parameter. Note that not all formats can be streamed in this way.
- A scheme specification of the form
:<scheme-name>:<scheme-args>.
- A system command line with either a "<" character at
the start, or a "|" character at the end
("<syscmd" or "syscmd|"). This
executes the given pipeline and reads from its standard output. This will
probably only work on unix-like systems.
In any case, compressed data in one of the supported compression formats (gzip,
Unix compress or bzip2) will be decompressed transparently.
- ucmdN=<cmds>
Specifies processing to be performed on upload table #N
as specified by parameter
uploadN, before any other processing has
taken place. The value of this parameter is one or more of the filter commands
described in SUN/256. If more than one is given, they must be separated by
semicolon characters (";"). This parameter can be repeated multiple
times on the same command line to build up a list of processing steps. The
sequence of commands given in this way defines the processing pipeline which
is performed on the table.
Commands may alteratively be supplied in an external file, by
using the indirection character '@'. Thus a value of
"@filename" causes the file filename to be read for
a list of filter commands to execute. The commands in the file may be
separated by newline characters and/or semicolons, and lines which are blank
or which start with a '#' character are ignored.
- ocmd=<cmds>
Specifies processing to be performed on the output table,
after all other processing has taken place. The value of this parameter is one
or more of the filter commands described in SUN/256. If more than one is
given, they must be separated by semicolon characters (";"). This
parameter can be repeated multiple times on the same command line to build up
a list of processing steps. The sequence of commands given in this way defines
the processing pipeline which is performed on the table.
Commands may alteratively be supplied in an external file, by
using the indirection character '@'. Thus a value of
"@filename" causes the file filename to be read for
a list of filter commands to execute. The commands in the file may be
separated by newline characters and/or semicolons, and lines which are blank
or which start with a '#' character are ignored.
- omode=out|meta|stats|count|checksum|cgi|discard|topcat|samp|tosql|gui
The mode in which the result table will be output. The
default mode is
out, which means that the result will be written as a
new table to disk or elsewhere, as determined by the
out and
ofmt parameters. However, there are other possibilities, which
correspond to uses to which a table can be put other than outputting it, such
as displaying metadata, calculating statistics, or populating a table in an
SQL database. For some values of this parameter, additional parameters
(
<mode-args>) are required to determine the exact behaviour.
Possible values are
- out
- meta
- stats
- count
- checksum
- cgi
- discard
- topcat
- samp
- tosql
- gui
Use the
help=omode flag or see SUN/256 for more information.
- out=<out-table>
The location of the output table. This is usually a
filename to write to. If it is equal to the special value "-" (the
default) the output table will be written to standard output.
This parameter must only be given if omode has its default
value of "out".
- ofmt=<out-format>
Specifies the format in which the output table will be
written (one of the ones in SUN/256 - matching is case-insensitive and you can
use just the first few letters). If it has the special value
"
(auto)" (the default), then the output filename will be
examined to try to guess what sort of file is required usually by looking at
the extension. If it's not obvious from the filename what output format is
intended, an error will result.
This parameter must only be given if omode has its default
value of "out".
- upnameN=<adql-identifier>
Identifier to use in server-side expressions for uploaded
table #N. In ADQL expressions, the table should be referred to as
"
TAP_UPLOAD.<label>".
The value must syntactically be an ADQL identifier
([A-Za-z][A-Za-z0-9_]*).
- tapurl=<url-value>
The base URL of a Table Access Protocol service. This is
the bare URL without a trailing "/[a]sync".
In the usual case, the default values of the various endpoints
(sync and async query submission, tables metadata, service-provided examples
etc) use this URL as a parent and append standard sub-paths.
In some cases however, determination of the endpoints is more
complicated, as determined by the interface parameter which may cause
endpoints to be read from the capabilities document at
tapurl/capabilities, and by other endpoint-specific parameters
(syncurl, asyncurl, tablesurl, capabilitiesurl,
availabilityurl, examplesurl) for fine tuning.
- interface=tap1.0|tap1.1|cap
Defines how the service endpoints and the version of the
TAP protocol to use for queries is determined. This may take one of the
following (case-insensitive) values:
- TAP1.0: The standard TAP endpoints are used, without examining the
service's capabilities document. The service is queried using version 1.0
of the TAP protocol.
- TAP1.1: The standard TAP endpoints are used, without examining the
service's capabilities document. The service is queried using version 1.1
of the TAP protocol.
- cap: The service's capabilities document is examined, and the
endpoints listed there are used.
The capabilities document, if used, is read from
tapurl/capabilities unless the capabilitiesurl parameter is
defined, in which case that is used.
The baseline value of all the TAP service endpoints (sync,
async, tables, capabilities, examples) are
determined by this parameter, but each of those endpoint values may be
overridden individually by other endpoint-specific parameters
(syncurl, asyncurl, tablesurl, capabilitiesurl,
availabilityurl, examplesurl)
For default (unauthenticated) access, the default value is usually
suitable.
- adql=<query-text>
Astronomical Data Query Language string specifying the
TAP query to execute. ADQL/S resembles SQL, so this string will likely start
with "SELECT".
- parse=true|false
Determines whether an attempt will be made to check the
syntax of the ADQL prior to submitting the query. If this is set true, and if
a syntax error is found, the task will fail with an error before any attempt
is made to submit the query.
- sync=true|false
Determines whether the TAP query is submitted in
synchronous or asynchronous mode. Synchronous (
true) means that the
result is retrieved over the same HTTP connection that the query is submitted
from. This is uncomplicated, but means if the query takes a long time it may
time out and the results will be lost. Asynchronous (
false) means that
the job is queued and results may be retrieved later. Normally this command
does the necessary waiting around and recovery of the result, though with
appropriate settings you can get
tapresume to pick it up for you later
instead. In most cases
false (the default) is preferred.
- maxrec=<nrow>
Sets the requested maximum row count for the result of
the query. The service is not obliged to respect this, but in the case that it
has a default maximum record count, setting this value may raise the limit. If
no value is set, the service's default policy will be used.
- destruction=<iso8601>
Posts an updated value of the UWS DESTRUCTION parameter
to the query job before it starts. This only makes sense for asynchronous jobs
(
sync=false).
The supplied value should be an ISO-8601-like string, giving the
new requested job destruction time. The service is not obliged to honour
this request. See UWS v1.0, sec 2.2.3.3.
- executionduration=<seconds>
Posts an updated value of the UWS EXECUTIONDURATION
parameter to the query job before it starts. This only makes sense for
asynchronous jobs (
sync=false).
The supplied value is an integer giving the maximum number of
wall-clock seconds for which the job is permitted to execute before being
forcibly terminated. A value of zero indicates unlimited duration. The
service is not obliged to honour this request. See UWS v1.0, sec
2.2.3.4.
- compress=true|false
If true, the service is requested to provide HTTP-level
compression for the response stream (Accept-Encoding header is set to
"
gzip", see RFC 2616). This does not guarantee that
compression will happen but if the service honours this request it may result
in a smaller amount of network traffic at the expense of more processing on
the server and client.
- upvotformat=TABLEDATA|BINARY|BINARY2
Determines how any uploaded tables will be serialized for
transmission to the TAP server. The supplied string is the name of one of the
defined VOTable serialization formats. The choice shouldn't affect any
results, though it may affect required bandwidth, and some services may
(though should not) have non-standard requirements for serialization format.
- language=<lang-name>
Language to use for the ADQL-like query. This will
usually be "ADQL" (the default), but may be set to some other value
supported by the service, for instance a variant indicating a different ADQL
version. Note that at present, setting it to "PQL" is not sufficient
to submit a PQL query.
- poll=<millisec>
Interval to wait between polling attempts, in
milliseconds. Asynchronous TAP queries can only find out when they are
complete by repeatedly polling the server to find out the job's status. This
parameter allows you to set how often that happens. Attempts to set it too low
(<50) will be rejected on the assumption that you're thinking in seconds.
- progress=true|false
If this parameter is set true, progress of the job is
reported to standard output as it happens.
- delete=finished|never|always|now
Determines under what circumstances the UWS job is to be
deleted from the server when its data is no longer required. If it is not
deleted, then the job is left on the TAP server and it can be accessed via the
normal UWS REST endpoints or using
tapresume until it is destroyed by
the server.
Possible values:
- finished: delete only if the job finished, successfully or not
- never: do not delete
- always: delete on command exit
- now: delete and return immediately