DBIx::DBStag::Cookbook(3pm)				User Contributed Perl Documentation			       DBIx::DBStag::Cookbook(3pm)

NAME

	 DBIx::DBStag::Cookbook - building and querying databases from XML

SYNOPSIS

	 stag-autoddl.pl
	 stag-storenode.pl
	 selectall_xml.pl

DESCRIPTION

       This will give an outline of how to build a normalised relational database from XML source data, set up SQL templates, issue relational
       queries that return hierarchical results (as XML or as perl objects), and autogenerate a web query front end for this data.

       Why would you want to do this? Well, it gives you the full power of the relational model and SQL, combined with the convenience of
       representations which allow for the nesting of data entities (SQL query results are typically flat relations which are inconvenient for
       complex hierarchical data).

       The dataset we will use is the CIA World Factbook.

       The web interface should end up looking something like this - http://www.godatabase.org/cgi-bin/wfb/ubiq.cgi
       <http://www.godatabase.org/cgi-bin/wfb/ubiq.cgi>

   AUTOGENERATING A RELATIONAL DATABASE
       Download CIA world factbook in XML format; this has kindly been made available by The University of Goettingen as part of their Mondial
       database project, see http://www.dbis.informatik.uni-goettingen.de/Mondial/ <http://www.dbis.informatik.uni-goettingen.de/Mondial/> for
       details.

       The actual XML file is available via http://www.dbis.informatik.uni-goettingen.de/Mondial/cia.xml <http://www.dbis.informatik.uni-
       goettingen.de/Mondial/cia.xml>

       Or from <http://www.godatabase.org/wfb/cia.xml>

       Pre-processing

       We need to do some pre-processing of the XML to make it more database-friendly. This is necessitated by the way Stag handles attributes
       (Stag prefers XML documents that have a simple tree format). We also want to turn XXX_id fields into XXX_ciaid, because we prefer to use
       XXX_id for surrogate keys in the database.

	 stag-mogrify.pl -w xml -r 's/text$/quant/'
				-r 's/id$/ciaid/'
				-r 's/(.*)-//'
				cia.xml > cia-pp.xml

       See also http://www.godatabase.org/wfb/cia-pp.xml <http://www.godatabase.org/wfb/cia-pp.xml>

       Generating the SQL DDL

       Next we generate the SQL CREATE TABLE statements

	 stag-autoddl.pl -t cia-pp2.xml cia-pp.xml > cia-schema.sql

       This does further post-processing of the XML, to make it suitable for relational storage; see the file cia-pp2.xml which is generated as a
       side-effect of running the above script.

       Load the database (the following instructions assume you have postgresql on your localhost; please consult your DBMS manual if this is not
       the case)

	 createdb cia
	 psql -a -e cia < cia-schema.sql >& create.log

       (check there are no errors in the log file)

       LOAD THE DATA

       Turn the processed XML into relations:

	 stag-storenode.pl -d dbi:Pg:dbname=cia cia-pp2.xml >& load.log

   FETCHING TREE DATA USING SQL
       You can issue SQL queries (using optional stag-specific extensions) and get the results back in a hierarchical format such as XML

       SQL to XML via the command line

       Fetch countries nested under continents:

	 selectall_xml.pl -d dbi:Pg:dbname=cia
	 "SELECT * FROM continent INNER JOIN country ON (continent.name=country.continent)"

       Or, edit a file containing the SQL (the following query fetches data on countries bordering other countries on different continents)

	 cat > myquery.sql
	 select c1.*, c2.*
	 from country AS c1
		  inner join borders on (c1.country_id = borders.country_id)
		  inner join country AS c2 on (borders.country=c2.ciaid)
	 where c1.continent != c2.continent
	 order by c1.name, c2.name
	 use nesting (set(c1(c2)));

       (the final clause is a DBStag SQL extension - it nests country c2 under country c1)

       Then query for XML

	 selectall_xml.pl -d dbi:Pg:dbname=cia -f myquery.sql > myresults.xml

       SQL to XML via the Interactive Query Shell

       Query the data using the stag query shell (qsh). You type in SQL queries, and get results back as XML (or any other tree format, such as
       indented text or S-Expressions).

       The following can be cut and pasted directly onto the unix command line:

       Simple query rooted at country:

	 stag-qsh -d dbi:Pg:dbname=cia
	 l
	 SELECT * FROM country INNER JOIN country_coasts USING (country_id)
	 WHERE country.name = 'France';

       (type q to quit stag-qsh)

       Or a more advanced query, still rooted at country

	 stag-qsh -d dbi:Pg:dbname=cia
	 l
	 SELECT *
	 FROM country
	      LEFT OUTER JOIN religions USING (country_id)
	      LEFT OUTER JOIN languages USING (country_id)
	      INNER JOIN continent ON (continent.name=country.continent)
	 WHERE continent.ciaid = 'australia'
	 USE NESTING (set(country(religions)(languages)(continent)));

       See DBIx::DBStag for more details on fetching hierarchical data from relational database

   USING TEMPLATES
       If you have a particular pattern of SQL you execute a lot, you can reuse this SQL by creating templates

       Creating Templates

       First create a place for your templates:

	 mkdir ./templates

       (do not change directory after this)

       The following command specifies a colon-separated path for directories containing templates (all templates must end with .stg)

	 setenv DBSTAG_TEMPLATE_DIRS ".:templates:/usr/local/share/sql/templates"

       Auto-generate templates (you can customize these later):

	 stag-autoschema.pl -w sxpr cia-pp2.xml > cia-stagschema.sxpr
	 stag-autotemplate.pl -no_pp -s cia -dir ./templates  cia-stagschema.sxpr

       The first command creates an S-Expression representation of the Schema; the second generates SQL templates from these.

       You may wish to examine a template:

	 more templates/cia-country.stg

       You can hand generate as many templates as you like; see DBIx::DBStag::SQLTemplate for more details

       For more example templates for this schema, see http://www.godatabase.org/cgi-bin/wfb/ubiq.cgi <http://www.godatabase.org/cgi-
       bin/wfb/ubiq.cgi>

       Executing Templates from the Command Line

       now execute a template from the command line:

	 selectall_xml.pl -d dbi:Pg:dbname=cia /cia-country country_name=Austria

       You should get back a tree (rooted in country), that looks similar to this:

	 <set>
	   <country>
	     <country_id>3</country_id>
	     <government>federal republic</government>
	     <population>8023244</population>
	     <total_area>83850</total_area>
	     <name>Austria</name>
	     <inflation>2.3</inflation>
	     ...
	     <languages>
	       <languages_id>1</languages_id>
	       <name>German</name>
	       <num>100</num>
	       <country_id>3</country_id>
	     </languages>
	     ...

       Executing Templates with the Stag Query Shell

       You can also do this interactively using qsh

       First, we need to inform stag-qsh what the schema is. The schema is used to determine which templates are appropriate. Later we will
       discover how to set up a resources file, which will allow stag to infer the schema.

       Call qsh from command line:

	 stag-qsh -d dbi:Pg:dbname=cia -s cia

       Interactive perl/qsh:

	 l
	 t cia-country
	 /borders_country=cid-cia-Germany

       (do not leave spaces at the beginning of the line)

       The above should fetch all countries bordering Germany

       If we prefer objects over hierarchical formats such as XML, we can do this using perl. For example, to print the religions of spanish
       speaking countries:

       Still in qsh (multi-line mode), type the following:

	 # find all Spanish-speaking countries
	 $dataset =
	   $dbh->selectall_stag(-template=>'cia-country',-bind=>{languages_name=>'Spanish'});
	 # get country objects from query results
	 @lcountry = $dataset->get_country;

	 foreach $country (@lcountry) {
	   printf("Country: %s
  Religions:%s
",
		  $country->sget_name,
		  join(' & ',
		       map {
			    $_->get_name.' '.$_->get_quant.'%'
		       } $country->get_religions))
	 }
	 print "

Done!
";
	 q

       See Data::Stag for more details on using Stag objects

   BUILDING A CGI/WEB INTERFACE
       We can construct a generic but powerful default cgi interface for our data, using ubiq.cgi, which should come with your distribution.

       You may have to modify some of the directories below, depending on your web server set up (we assume Apache here).

       We want to create the CGI, and give it access to our templates:

	 mkdir /usr/local/httpd/cgi-bin/cia
	 cp templates/*.stg /usr/local/httpd/cgi-bin/cia
	 cp `which ubiq.cgi` /usr/local/httpd/cgi-bin/cia
	 chmod +x /usr/local/httpd/cgi-bin/cia/ubiq.cgi
	 mkdir /usr/local/httpd/cgi-bin/cia/cache
	 chmod 777 /usr/local/httpd/cgi-bin/cia/cache

       Set up the environment for the CGI script. It must be able to see the templates and the necessary perl libraries (if not installed system-
       wide)

	 cat > /usr/local/httpd/cgi-bin/cia/dbenv.pl
	 $ENV{DBSTAG_DBIMAP_FILE} = "./resources.conf";
	 $ENV{DBSTAG_TEMPLATE_DIRS} = ".:./templates:/usr/local/share/sql/templates";
	 $ENV{STAGLIB} = "/users/me/lib/DBIx-DBStag:/users/me/lib/stag";

       We must create a basic resources file, currently containing one db:

	 cat > /usr/local/httpd/cgi-bin/cia/resources.conf
	 cia		  rdb		    Pg:cia	  schema=cia

       Fields are whitespace delimited; do not leave a space before the initial 'cia'

       (note that if you set DBSTAG_DBIMAP_FILE to the avove file on the command line, you can use the shortened name of cia instead of
       dbi:Pg:dbname=cia)

       You should be able to use the interface via http://localhost/cgi-bin/cia/ubiq.cgi

       You can customize this by overriding some of the existing display functions;

	 cat > /usr/local/httpd/cgi-bin/cia/ubiq-customize.pl
	 # --- CUSTOM SETTINGS
	 {
	  no warnings 'redefine';

	  *g_title = sub {
	      "U * B * I * Q - CIA World Factbook";
	  };
	  *short_intro = sub {
	      "Demo interface to CIA World Factbook"
	  };
	  add_initfunc(sub {
			  $dbname = 'cia';
			  $schema = 'cia';
		      });
	 }

       From here on you can customise the web interface, create new templates, integrate this with other data. Consult DBIx::DBStag and the script
       ubiq.cgi for further details.

   FURTHER EXPLORATION
       This cookbook has focused on an example with relatively simple XML, with only a few layers of nesting.

       There is a more complex example you can download from the Mondial project site here:
       http://www.dbis.informatik.uni-goettingen.de/Mondial/mondial-2.0.xml <http://www.dbis.informatik.uni-goettingen.de/Mondial/mondial-2.0.xml>

       This also integrates data on cities, which increases the depth of the XML tree.

       You could use the tutorial above to try and turn this XML into a database.

WEBSITE

       <http://stag.sourceforge.net>

AUTHOR

       Chris Mungall

	 cjm at fruitfly dot org

COPYRIGHT

       Copyright (c) 2002 Chris Mungall

       This module is free software.  You may distribute this module under the same terms as perl itself

perl v5.12.4							    2010-01-21					       DBIx::DBStag::Cookbook(3pm)