Doc: add a glossary entry for "domain".

Anton Voloshin and Jürgen Purtz, reviewed by Laurenz Albe

Discussion: https://postgr.es/m/2ea65bdf-1380-f088-02bd-ff1a31ed265c@postgrespro.ru

doc/src/sgml/charset.sgml

@@ -346,7 +346,8 @@ initdb --locale=sv_SE
     collation.  (The built-in collatable data types are
     <type>text</type>, <type>varchar</type>, and <type>char</type>.
     User-defined base types can also be marked collatable, and of course
-    a domain over a collatable data type is collatable.)  If the
+    a <glossterm linkend="glossary-domain">domain</glossterm> over a
+    collatable data type is collatable.)  If the
     expression is a column reference, the collation of the expression is the
     defined collation of the column.  If the expression is a constant, the
     collation is the default collation of the data type of the

doc/src/sgml/earthdistance.sgml

@@ -50,7 +50,8 @@
   <para>
    Data is stored in cubes that are points (both corners are the same) using 3
    coordinates representing the x, y, and z distance from the center of the
-   Earth.  A domain <type>earth</type> over <type>cube</type> is provided, which
+   Earth.  A <glossterm linkend="glossary-domain">domain</glossterm>
+   <type>earth</type> over type <type>cube</type> is provided, which
    includes constraint checks that the value meets these restrictions and
    is reasonably close to the actual surface of the Earth.
   </para>

doc/src/sgml/glossary.sgml

@@ -390,8 +390,7 @@
      A restriction on the values of data allowed within a
      <glossterm linkend="glossary-table">table</glossterm>,
      or in attributes of a
-     <!-- XXX Should have term "domain". Need term "type" for that. -->
-     <firstterm>domain</firstterm>.
+     <glossterm linkend="glossary-domain">domain</glossterm>.
     </para>
     <para>
      For more information, see
@@ -508,6 +507,20 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-domain">
+   <glossterm>Domain</glossterm>
+   <glossdef>
+    <para>
+     A user-defined data type that is based on another underlying data type.
+     It acts the same as the underlying type except for possibly restricting
+     the set of allowed values.
+    </para>
+    <para>
+     For more information, see <xref linkend="domains"/>.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-durability">
    <glossterm>Durability</glossterm>
    <glossdef>

doc/src/sgml/information_schema.sgml

@@ -2577,7 +2577,8 @@
   <title><literal>domains</literal></title>
 
   <para>
-   The view <literal>domains</literal> contains all domains defined in the
+   The view <literal>domains</literal> contains all
+   <glossterm linkend="glossary-domain">domains</glossterm> defined in the
    current database.  Only those domains are shown that the current user has
    access to (by way of being the owner or having some privilege).
   </para>

doc/src/sgml/lo.sgml

@@ -55,7 +55,8 @@
 
   <para>
    The module also provides a data type <type>lo</type>, which is really just
-   a domain of the <type>oid</type> type.  This is useful for differentiating
+   a <glossterm linkend="glossary-domain">domain</glossterm> over
+   the <type>oid</type> type.  This is useful for differentiating
    database columns that hold large object references from those that are
    OIDs of other things.  You don't have to use the <type>lo</type> type to
    use the trigger, but it may be convenient to use it to keep track of which

doc/src/sgml/rowtypes.sgml

@@ -84,7 +84,8 @@ CREATE TABLE inventory_item (
   restriction of the current implementation: since no constraints are
   associated with a composite type, the constraints shown in the table
   definition <emphasis>do not apply</emphasis> to values of the composite type
-  outside the table.  (To work around this, create a domain over the composite
+  outside the table.  (To work around this, create a
+  <glossterm linkend="glossary-domain">domain</glossterm> over the composite
   type, and apply the desired constraints as <literal>CHECK</literal>
   constraints of the domain.)
  </para>