[docs] fix API xreferences in tutorial

docs/source/tutorial.rst

@@ -17,7 +17,7 @@ temporary (i.e. not preserved across system reboots) directory.
    it or, alternatively, as an argument to the :class:`~.core.LegendMetadata`
    constructor. Recommended if a custom legend-metadata_ is needed.
 
-:class:`~.core.LegendMetadata` is a :class:`~.textdb.textdb` object, which
+:class:`~.core.LegendMetadata` is a :class:`~.textdb.TextDB` object, which
 implements an interface to a database of text files arbitrary scattered in a
 filesystem. ``TextDB`` does not assume any directory structure or file naming.
 
@@ -83,7 +83,7 @@ Mappings of metadata to time periods, data taking systems etc. are specified
 through YAML files (`specification
 <https://legend-exp.github.io/legend-data-format-specs/dev/metadata>`_).
 If a ``validity.yaml`` file is present in a directory, ``TextDB``
-exposes the :meth:`~.textdb.textdb.on` interface to perform a query.
+exposes the :meth:`~.textdb.TextDB.on` interface to perform a query.
 
 Let's assume the ``legend-metadata`` directory from the example above contains
 the following file:
@@ -151,7 +151,7 @@ channel map:
 Remapping and grouping metadata
 -------------------------------
 
-A second important method of ``TextDB`` is :meth:`.textdb.map`, which allows to
+A second important method of ``TextDB`` is :meth:`.TextDB.map`, which allows to
 query ``(key, value)`` dictionaries with an alternative unique key defined in
 ``value``. A typical application is querying parameters in a channel map
 corresponding to a certain DAQ channel:
@@ -167,10 +167,10 @@ corresponding to a certain DAQ channel:
  ...
 
 If the requested key is not unique, an exception will be raised.
-:meth:`.textdb.map` can, however, handle non-unique keys too and return a
+:meth:`.TextDB.map` can, however, handle non-unique keys too and return a
 dictionary of matching entries instead, keyed by an arbitrary integer to allow
-further :meth:`.textdb.map` calls. The behavior is achieved by using
-:meth:`.textdb.group` or by setting the ``unique`` argument flag. A typical
+further :meth:`.TextDB.map` calls. The behavior is achieved by using
+:meth:`.TextDB.group` or by setting the ``unique`` argument flag. A typical
 application is retrieving all channels attached to the same CC4:
 
 >>> chmap = lmeta.hardware.configuration.channelmaps.on(datetime.now())