Deprecating image and spectrum as registry servicetype-s

In an attempt to accomodate the concerns brought up in
astropy#449 (comment),
we also explain a bit why image and spectrum are being deprecated.
we still raise deprecation warnings (rather than something else), as
that is, I think, what we are doing (and should be doing): We are saying
that we discourage people to use these two strings and reserve the
right to drop them one day.

CHANGES.rst

@@ -49,6 +49,9 @@ Enhancements and Fixes
 Deprecations and Removals
 -------------------------
 
+- Deprecating the use of "image" and "spectrum" in registry Servicetype
+  constraints [#449]
+
 
 1.5.2 (2024-05-22)
 ==================

docs/registry/index.rst

@@ -303,13 +303,13 @@ instance.  The opening example could be written like this:
 
   >>> from astropy.coordinates import SkyCoord
   >>> my_obj = SkyCoord.from_name("Bellatrix")
-  >>> for res in registry.search(waveband="infrared", servicetype="spectrum"):
+  >>> for res in registry.search(waveband="infrared", servicetype="ssap"):
   ...     print(res.service.search(pos=my_obj, size=0.001))
   ...
 
 In reality, you will have to add some error handling to this kind of
 all-VO queries: in a wide and distributed network, some service is
-always down.  See `Appendix: Robust All-VO Queries`_
+always down.  See `Appendix: Robust All-VO Queries`_.
 
 The central point is: With a ``servicetype`` constraint,
 each result has a well-defined ``service`` attribute that contains some
@@ -644,3 +644,7 @@ run all-VO queries without reading at least this sentence):
      148.204840298431    29.1690999975089
            243.044008          -51.778222
    321.63278049999997 -54.579285999999996
+
+Note that even this is not enough to reliably cover use cases like „give
+me all images of M1 in the X-Ray in the VO“.  In some future version,
+pyVO will come with higher-level functionality for such tasks.

pyvo/registry/rtcons.py

@@ -11,10 +11,12 @@
 """
 
 import datetime
+import warnings
 
 from astropy import units as u
 from astropy import constants
 from astropy.coordinates import SkyCoord
+from astropy.utils.exceptions import AstropyDeprecationWarning
 import numpy
 
 from ..dal import query as dalq
@@ -356,16 +358,15 @@ class Servicetype(Constraint):
 
     The constraint normally is a custom keyword, one of:
 
-    * ``image`` (image services; at this point equivalent to sia, but
-      scheduled to include sia2, too)
     * ``sia`` (SIAP version 1 services)
     * ``sia2`` (SIAP version 2 services)
-    * ``spectrum``, ``ssa``, ``ssap`` (all synonymous for spectral
-      services, prefer ``spectrum``)
+    * ``ssa``, ``ssap`` (synonymous for SSAP services)
     * ``scs``, ``conesearch`` (synonymous for cone search services, prefer
       ``scs``)
     * ``line`` (for SLAP services)
     * ``tap``, ``table`` (synonymous for TAP services, prefer ``tap``)
+    * ``image`` (a deprecated alias for sia)
+    * ``spectrum`` (a deprecated alias for ssap)
 
     You can also pass in the standards' ivoid (which
     generally looks like
@@ -377,6 +378,15 @@ class Servicetype(Constraint):
     Multiple service types can be passed in; a match in that case
     is for records having any of the service types passed in.
 
+    Contrary to what the names of the service types may suggest,
+    “image” and "spectrum" do *not* select all resources serving images
+    or spectra.  For instance, at the moment you would have to search for
+    images served in three different ways: SIAv1, SIAv2, and ObsTAP. Against
+    that, “image” only selects SIAv1, and "spectrum" similarly omits ObsTAP.  A
+    global discovery module is under active development to provide global
+    dataset discovery. When it is ready, these two misleading options may be
+    removed.
+
     The match is literal (i.e., no patterns are allowed); this means
     that you will not receive records that only have auxiliary
     services, which is what you want when enumerating all services
@@ -401,6 +411,13 @@ def __init__(self, *stds):
         self.extra_fragments = []
 
         for std in stds:
+            if std in ('image', 'spectrum'):
+                warnings.warn(AstropyDeprecationWarning(
+                    f"The '{std}' servicetype is deprecated.  See"
+                    " https://pyvo.readthedocs.io/en/latest/api/pyvo.registry"
+                    ".Servicetype.html#pyvo.registry.Servicetype"
+                    " for more information."))
+
             if std in SERVICE_TYPE_MAP:
                 self.stdids.add(SERVICE_TYPE_MAP[std])
             elif "://" in std:

pyvo/registry/tests/test_rtcons.py

@@ -9,6 +9,8 @@
 from astropy.time import Time
 from astropy import units as u
 from astropy.coordinates import SkyCoord
+from astropy.utils.exceptions import AstropyDeprecationWarning
+
 import numpy
 import pytest
 
@@ -141,13 +143,13 @@ def test_fulluri(self):
                 == "standard_id IN ('http://extstandards/invention')")
 
     def test_multi(self):
-        assert (rtcons.Servicetype("http://extstandards/invention", "image"
+        assert (rtcons.Servicetype("http://extstandards/invention", "sia"
                                    ).get_search_condition(FAKE_GAVO)
                 == "standard_id IN ('http://extstandards/invention',"
                 " 'ivo://ivoa.net/std/sia')")
 
     def test_includeaux(self):
-        assert (rtcons.Servicetype("http://extstandards/invention", "image"
+        assert (rtcons.Servicetype("http://extstandards/invention", "sia"
                                    ).include_auxiliary_services().get_search_condition(FAKE_GAVO)
                 == "standard_id IN ('http://extstandards/invention',"
                 " 'http://extstandards/invention#aux',"
@@ -179,6 +181,16 @@ def test_sia2_aux(self):
                     " OR standard_id like 'ivo://ivoa.net/std/sia#query-2.%'"
                     " OR standard_id like 'ivo://ivoa.net/std/sia#query-aux-2.%'"))
 
+    def test_image_deprecated(self):
+        with pytest.warns(AstropyDeprecationWarning):
+            assert (rtcons.Servicetype("image").get_search_condition(FAKE_GAVO)
+                == "standard_id IN ('ivo://ivoa.net/std/sia')")
+
+    def test_spectrum_deprecated(self):
+        with pytest.warns(AstropyDeprecationWarning):
+            assert (rtcons.Servicetype("spectrum").get_search_condition(FAKE_GAVO)
+                == "standard_id IN ('ivo://ivoa.net/std/ssa')")
+
 
 @pytest.mark.usefixtures('messenger_vocabulary')
 class TestWavebandConstraint: