linkend="glossary-role">roles</glossterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="sql-revoke"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-role">
   <glossterm>Role</glossterm>
   <glossdef>
    <para>
     A collection of access privileges to the
     <glossterm linkend="glossary-database">instance</glossterm>.
     Roles are themselves a privilege that can be granted to other roles.
     This is often done for convenience or to ensure completeness
     when multiple <glossterm linkend="glossary-user">users</glossterm> need
     the same privileges.
    </para>
    <para>
     For more information, see
     <xref linkend="sql-createrole"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-rollback">
   <glossterm>Rollback</glossterm>
   <glossdef>
    <para>
     A command to undo all of the operations performed since the beginning
     of a <glossterm linkend="glossary-transaction">transaction</glossterm>.
    </para>
    <para>
     For more information, see
     <xref linkend="sql-rollback"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-routine">
   <glossterm>Routine</glossterm>
   <glossdef>
    <para>
     A defined set of instructions stored in the database system
     that can be invoked for execution.
     A routine can be written in a variety of programming
     languages.  Routines can be
     <glossterm linkend="glossary-function">functions</glossterm>
     (including set-returning functions and
     <glossterm linkend="glossary-trigger">trigger functions</glossterm>),
     <glossterm linkend="glossary-aggregate">aggregate functions</glossterm>,
     and <glossterm linkend="glossary-procedure">procedures</glossterm>.
    </para>
    <para>
     Many routines are already defined within <productname>PostgreSQL</productname>
     itself, but user-defined ones can also be added.
    </para>
   </glossdef>
  </glossentry>

  <glossentry>
   <glossterm>Row</glossterm>
   <glosssee otherterm="glossary-tuple" />
  </glossentry>

  <glossentry id="glossary-savepoint">
   <glossterm>Savepoint</glossterm>
   <glossdef>
    <para>
     A special mark in the sequence of steps in a
     <glossterm linkend="glossary-transaction">transaction</glossterm>.
     Data modifications after this point in time may be reverted
     to the time of the savepoint.
    </para>
    <para>
     For more information, see
     <xref linkend="sql-savepoint"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry id="glossary-schema">
   <glossterm>Schema</glossterm>
   <glossdef>
    <para>
     A schema is a namespace for
     <glossterm linkend="glossary-sql-object">SQL objects</glossterm>,
     which all reside in the same
     <glossterm linkend="glossary-database">database</glossterm>.
     Each SQL object must reside in exactly one schema.
    </para>
    <para>
     All system-defined SQL objects reside in schema <literal>pg_catalog</literal>.
    </para>
   </glossdef>
   <glossdef>
    <para>
     More generically, the term <firstterm>schema</firstterm> is used to mean
     all data descriptions (<glossterm linkend="glossary-table">table</glossterm> definitions,
     <glossterm linkend="glossary-constraint">constraints</glossterm>, comments, etc.)
     for a given <glossterm linkend="glossary-database">database</glossterm> or
     subset thereof.
    </para>
    <para>
     For more information, see
     <xref linkend="ddl-schemas"/>.
    </para>
   </glossdef>
  </glossentry>

  <glossentry>
   <glossterm>Segment</glossterm>
   <glosssee otherterm="glossary-file-segment" />
  </glossentry>

  <glossentry id="glossary-select">
   <glossterm>Select</glossterm>
   <glossdef>
    <para>
     The <acronym>SQL</acronym> command used to request data from a
     <glossterm linkend="glossary-database">database</glossterm>.
     Normally, <command>SELECT</command> commands are not expected to modify the
     <glossterm linkend="glossary-database">database</glossterm>