25. EPN-TAP 2: Querying EPN-TAP

EPN-TAP services are queried like any other TAP service. Use a table browser to see what columns are available or check the standard.

for svcrow in epn_services.table():
  service = pyvo.dal.TAPService(svcrow["accessurl"])
  for table_name in svcrow["tables"].split("#"):
    print("\nQuerying {} on {}".format(
      table_name, svcrow["accessurl"]))
    for row in vohelper.run_sync_resilient(service,
        "SELECT TOP 2 * FROM {} WHERE target_name='Mars'".format(
        table_name).table():
      print(row)

[See epnquery.py]

This looks a bit more complex than before because a single service can have multiple EPN-TAP tables, so we have another iteration to go, and we need to fiddle in the table names into the queries.

Things are a bit more complex than in anything we’ve seen so far because EPN-TAP lets people stick in almost any kind of data into such tables, and what your access_url points to – spectra, profiles of elemental abundances, odd magnetospheric data, or nothing at all – is impossible to tell before at least inspecting the dataproduct_type column (and even then your average non-solar-system astronomer may be stumped… )

Of course, you want to do smarter things than print a row.