Re: Some Documentation Changes

Patch applied. Thanks.

---------------------------------------------------------------------------

Christopher Browne wrote:
> 1. In keeping with the recent discussion that there should be more
> said about views, stored procedures, and triggers, in the tutorial, I
> have added a bit of verbiage to that end.
>
> 2. Some formatting changes to the datetime discussion, as well as
> addition of a citation of a relevant book on calendars.
>
> Index: advanced.sgml
> ===================================================================
> RCS file: /projects/cvsroot/pgsql-server/doc/src/sgml/advanced.sgml,v
> retrieving revision 1.38
> diff -c -u -r1.38 advanced.sgml
> --- advanced.sgml 29 Nov 2003 19:51:36 -0000 1.38
> +++ advanced.sgml 30 Dec 2003 01:58:24 -0000
> @@ -65,10 +65,24 @@
>
> <para>
> Views can be used in almost any place a real table can be used.
> - Building views upon other views is not uncommon.
> + Building views upon other views is not uncommon. You may cut down
> + on the difficulty of building complex queries by constructing them
> + in smaller, easier-to-verify pieces, using views. Views may be
> + used to reveal specific table columns to users that legitimately
> + need access to some of the data, but who shouldn't be able to look
> + at the whole table.
> </para>
> - </sect1>
>
> + <para>
> + Views differ from <quote> real tables </quote> in that they are
> + not, by default, updatable. If they join together several tables,
> + it may be troublesome to update certain columns since the
> + <emphasis>real</emphasis> update that must take place requires
> + identifying the relevant rows in the source tables. This is
> + discussed further in <xref linkend="rules-views-update">.
> + </para>
> +
> + </sect1>
>
> <sect1 id="tutorial-fk">
> <title>Foreign Keys</title>
> @@ -387,6 +401,169 @@
> </para>
> </sect1>
>
> + <sect1 id="tutorial-storedprocs">
> + <title> Stored Procedures </title>
> +
> + <indexterm zone="tutorial-storedprocs">
> + <primary>stored procedures</primary>
> + </indexterm>
> +
> + <para> Stored procedures are code that runs inside the database
> + system. Numerous languages may be used to implement functions and
> + procedures; most built-in code is implemented in C. The
> + <quote>basic</quote> loadable procedural language for
> + <productname>PostgreSQL</productname> is <xref linkid="plpgsql">.
> + Numerous other languages may also be used, including <xref
> + linkid="plperl">, <xref linkid="pltcl">, and <xref
> + linkid="plpython">.
> + </para>
> +
> + <para> There are several ways that stored procedures are really
> + helpful:
> +
> + <itemizedlist>
> +
> + <listitem><para> To centralize data validation code into the
> + database </para>
> +
> + <para> Your system may use client software written in several
> + languages, perhaps with a <quote>web application</quote>
> + implemented in PHP, a <quote>server application</quote> implemented
> + in Java, and a <quote> report writer</quote> implemented in Perl.
> + In the absence of stored procedures, you will likely find that data
> + validation code must be implemented multiple times, in multiple
> + languages, once for each application.</para>
> +
> + <para> By implementing data validation in stored procedures,
> + running in the database, it can behave uniformly for all these
> + systems, and you do not need to worry about synchronizing
> + validation procedures across the languages.</para>
> +
> + </listitem>
> +
> + <listitem><para> Reducing round trips between client and server
> + </para>
> +
> + <para>A stored procedure may submit multiple queries, looking up
> + information and adding in links to additional tables. This takes
> + place without requiring that the client submit multiple queries,
> + and without requiring any added network traffic.
> + </para>
> +
> + <para> As a matter of course, the queries share a single
> + transaction context, and there may also be savings in the
> + evaluation of query plans, that will be similar between invocations
> + of a given stored procedure. </para></listitem>
> +
> + <listitem><para> To simplify queries. </para>
> +
> + <para> For instance, if you are commonly checking the TLD on domain
> + names, you might create a stored procedure for this purpose, and so
> + be able to use queries such as <command> select domain, tld(domain)
> + from domains; </command> instead of having to put verbose code
> + using <function>substr()</function> into each query.
> + </para>
> +
> + <para> It is particularly convenient to use scripting languages
> + like Perl, Tcl, and Python to <quote>grovel through strings</quote>
> + since they are designed for <quote>text processing.</quote></para>
> +
> + <para> The binding to the R statistical language allows
> + implementing complex statistical queries inside the database,
> + instead of having to draw the data out.
> + </listitem>
> +
> + <listitem><para> Increasing the level of abstraction</para>
> +
> + <para> If data is accessed exclusively through stored procedures,
> + then the structures of tables may be changed without there needing
> + to be any visible change in the API used by programmers. In some
> + systems, users are <emphasis>only</emphasis> allowed access to
> + stored procedures to update data, and cannot do direct updates to
> + tables.
> + </para>
> +
> + </listitem>
> +
> + </itemizedlist>
> + </para>
> +
> + <para> These benefits build on one another: careful use of stored
> + procedures can simultaneously improve reliability and performance,
> + whilst simplifying database access code and improving portability
> + across client platforms and languages. For instance, consider that
> + a stored procedure can cheaply query tables in the database to
> + validate the correctness of data provided as input. </para>
> +
> + <para> Instead of requiring a whole series of queries to create an
> + object, and to look up parent/subsidiary objects to link it to, a
> + stored procedure can do all of this efficiently in the database
> + server, improving performance, and eliminating whole classes of
> + errors. </para>
> +
> + </sect1>
> +
> + <sect1 id="tutorial-triggers">
> + <title> Triggers </title>
> +
> + <indexterm zone="tutorial-triggers">
> + <primary>triggers</primary>
> + </indexterm>
> +
> + <para> Triggers allow running a function either before or after
> + update (<command>INSERT</command>, <command>DELETE</command>,
> + <command>UPDATE</command>) operations, which can allow you to do
> + some very clever things. </para>
> +
> + <itemizedlist>
> +
> + <listitem><para> Data Validation </para>
> +
> + <para> Instead of explicitly coding validation checks as part of a
> + stored procedure, they may be introduced as <command>BEFORE</command>
> + triggers. The trigger function checks the input values, raising an
> + exception if it finds invalid input.</para>
> +
> + <para> Note that this is how foreign key checks are implemented in
> + <productname>PostgreSQL</productname>; when you define a foreign
> + key, you will see a message similar to the following:
> +<screen>
> +NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
> +</screen></para>
> +
> + <para> In some cases, it may be appropriate for a trigger function
> + to insert data in order to <emphasis>make</emphasis> the input valid. For
> + instance, if a newly created object needs a status code in a status
> + table, the trigger might automatically do that.</para>
> + </listitem>
> +
> + <listitem><para> Audit logs </para>
> +
> + <para> One may use <command>AFTER</command> triggers to monitor updates to
> + vital tables, and <command>INSERT</command> entries into log tables to
> + provide a more permanent record of those updates. </para>
> + </listitem>
> +
> + <listitem><para> Replication </para>
> +
> + <para> The <application>RServ</application> replication system uses
> + <command>AFTER</command> triggers to track which rows have changed on the
> + <quote>master</quote> system and therefore need to be copied over to
> + <quote>slave</quote> systems.</para>
> +
> + <para> <command>
> + CREATE TRIGGER "_rserv_trigger_t_" AFTER INSERT OR DELETE OR UPDATE ON "my_table"
> + FOR EACH ROW EXECUTE PROCEDURE "_rserv_log_" ('10');
> + </command></para>
> + </listitem>
> +
> + </itemizedlist>
> +
> + <para> Notice that there are strong parallels between what can be
> + accomplished using triggers and stored procedures, particularly in
> + regards to data validation. </para>
> +
> + </sect1>
>
> <sect1 id="tutorial-conclusion">
> <title>Conclusion</title>
> Index: datetime.sgml
> ===================================================================
> RCS file: /projects/cvsroot/pgsql-server/doc/src/sgml/datetime.sgml,v
> retrieving revision 2.39
> diff -c -u -r2.39 datetime.sgml
> --- datetime.sgml 1 Dec 2003 20:34:53 -0000 2.39
> +++ datetime.sgml 30 Dec 2003 01:58:25 -0000
> @@ -11,8 +11,8 @@
> strings, and are broken up into distinct fields with a preliminary
> determination of what kind of information may be in the
> field. Each field is interpreted and either assigned a numeric
> - value, ignored, or rejected.
> - The parser contains internal lookup tables for all textual fields,
> + value, ignored, or rejected.</para>
> + <para> The parser contains internal lookup tables for all textual fields,
> including months, days of the week, and time
> zones.
> </para>
> @@ -1056,21 +1056,21 @@
> years.
> </para>
>
> - <para>
> - The papal bull of February 1582 decreed that 10 days should be dropped
> - from October 1582 so that 15 October should follow immediately after
> - 4 October.
> - This was observed in Italy, Poland, Portugal, and Spain. Other Catholic
> - countries followed shortly after, but Protestant countries were
> - reluctant to change, and the Greek orthodox countries didn't change
> - until the start of the 20th century.
> -
> - The reform was observed by Great Britain and Dominions (including what is
> - now the USA) in 1752.
> - Thus 2 September 1752 was followed by 14 September 1752.
> + <para> The papal bull of February 1582 decreed that 10 days should
> + be dropped from October 1582 so that 15 October should follow
> + immediately after 4 October.</para>
> +
> + <para> This was observed in Italy, Poland, Portugal, and Spain.
> + Other Catholic countries followed shortly after, but Protestant
> + countries were reluctant to change, and the Greek orthodox countries
> + didn't change until the start of the 20th century.</para>
> +
> + <para> The reform was observed by Great Britain and Dominions
> + (including what is now the USA) in 1752. Thus 2 September 1752 was
> + followed by 14 September 1752.</para>
>
> - This is why Unix systems have the <command>cal</command> program
> - produce the following:
> + <para> This is why Unix systems have the <command>cal</command>
> + program produce the following:
>
> <screen>
> $ <userinput>cal 9 1752</userinput>
> @@ -1094,19 +1094,24 @@
> </para>
> </note>
>
> - <para>
> - Different calendars have been developed in various parts of the
> - world, many predating the Gregorian system.
> + <para> Different calendars have been developed in various parts of
> + the world, many predating the Gregorian system.</para>
>
> - For example,
> - the beginnings of the Chinese calendar can be traced back to the 14th
> - century BC. Legend has it that the Emperor Huangdi invented the
> - calendar in 2637 BC.
> + <para> For example, the beginnings of the Chinese calendar can be
> + traced back to the 14th century BC. Legend has it that the Emperor
> + Huangdi invented the calendar in 2637 BC.</para>
>
> - The People's Republic of China uses the Gregorian calendar
> - for civil purposes. The Chinese calendar is used for determining
> - festivals.
> + <para> The People's Republic of China uses the Gregorian calendar
> + for civil purposes. The Chinese calendar is used for determining
> + festivals.
> </para>
> +
> + <para> If you are interested in this sort of thing, <citation>
> + Calendrical Calculations: The Millennium Edition </citation> by by
> + Edward M. Reingold and Nachum Dershowitz is an excellent reference,
> + describing some 25 calendars, and providing software for displaying
> + them and converting between them.</para>
> +
> </sect1>
> </appendix>
> --
> let name="cbbrowne" and tld="libertyrms.info" in String.concat "@" [name;tld];;
> <http://dev6.int.libertyrms.com/>
> Christopher Browne
> (416) 646 3304 x124 (land)
>
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