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\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
<
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