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>
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/> for details.The actual XML file is available via <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>
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 XMLSQL 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 templatesCreating 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>
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\n Religions:%s\n",
$country->sget_name,
join(' & ',
map {
$_->get_name.' '.$_->get_quant.'%'
} $country->get_religions))
}
print "\n\nDone!\n";
\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>
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 MungallThis module is free software. You may distribute this module under the same terms as perl itself