README for DBIx::DBStag
========================

*  *  For installation instructions, see the file INSTALL  *  *

Currently DBStag is focused towards postgresql. The test suite will
not work with mysql, but most of the code seems to be fine with it. I
haven't tried with other DBMSs but most of the code should be DBMS
independent.

For documentation on how to use DBIx::DBStag, either

type

  perldoc DBIx/DBStag.pm

or follow the instructions in INSTALL, and type

  man DBIx::DBStag

QUERYING
--------

in perl:
         use DBIx::DBStag;
         my $dbh = DBIx::DBStag->connect("dbi:Pg:dbname=moviedb");
         my $sql = q[
                     SELECT
                      studio.*,
                      movie.*,
                      star.*
                     FROM
                      studio NATURAL JOIN
                      movie NATURAL JOIN
                      movie_to_star NATURAL JOIN
                      star
                     WHERE
                      movie.genre = 'sci-fi' AND star.lastname = 'Fisher';
                    ];
         my $dataset = $dbh->selectall_stag($sql);

in unix:

         selectall_xml.pl -d 'dbi:Pg:dbname=moviedb' -f my_queries/query.sql


STORING DATA
------------

in perl:

$db = DBIx::DBSchema->new(...);
$stag = Data::Stag->parse("file.xml");
$db->store($stag);

in unix:

stag-storenode.pl -d <dsn> file.xml

The DB columns and tables should match the elements

AUTOGENERATING DATABASES
------------------------

It is possible to automatically generate a database schema and
populate it directly from XML files (or from Stag objects or other
Stag compatible files). Of course, this is no substitute for proper
relational design, but often it can be necessary to quickly generate
databases from heterogeneous XML data sources, for the purposes of
data mining.

There are 3 steps involved:

1. Prepare the input XML (for instance, modifying db reserved words).
2. Autogenerate the CREATE TABLE statements, and make a db from these.
3. Store the XML data in the database.

Step 1: Prepare input file
~~~~~~~~~~~~~~~~~~~~~~~~~~

You may need to make modifications to your XML before it can be used
to make a schema. If your XML elements contain any words that are
reserved by your DB you should change these.

Any XML processing tool (eg XSLT) can be used. Alternatively you can
use the script 'stag-mogrify'

e.g. to get rid of '-' characters (this is how Stag treates
attributes) and to change the element with postgresql reserved word
'date', do this:

  stag-mogrify.pl -xml -r 's/^date$/moddate/' -r 's/\-//g' data.xml > data.mog.xml

You may also need to explicitly make elements where you will need
linking tables. For instance, if the relationship between 'movie' and
'star' is many-to-many, and your input data looks like this:

  (movie
   (name "star wars")
   (star
    (name "mark hamill")))

You will need to *interpose* an element between these two, like this:

  (movie
   (name "star wars")
   (movie2star
    (star
     (name "mark hamill"))))

you can do this with the -i switch:

  stag-mogrify.pl -xml -i movie,star,movie2star data.xml > data.mog.xml

or if you simply do:

  stag-mogrify.pl -xml -i star data.xml > data.mog.xml

the mogrifier will simply interpose an element above every time it
sees 'star'; the naming rule is to use the two elements with an
underscore between (in this case, 'movie_star').

Step 2: Generating CREATE TABLE statements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Use the stag-autoddl.pl script;

  stag-autoddl.pl data.mog.xml > table.sql

The default rule is to create foreign keys from the nested element to
the outer element; you will want linking tables tobe treated
differently (a linking table will point to parent and child elements).

  stag-autoddl.pl -l movie2star -l star2character data.mog.xml > table.sql

Once you have done this, load the statements into your db; eg for postgresql
(for other databases, use L<SQL::Translator>)

  psql -a mydb < table.sql

If something goes wrong, go back to step 1 and sort it out!

Note that certain rules are followed: ever table generated gets a
surrogate primary key of type 'serial'; this is used to generate
foreign key relationships. The rule used is primary and foreign key
names are the name of the table with the '_id' suffix.

Feel free to modify the autogenerated schema at this stage (eg add
uniqueness constraints)

Step 3: Store the data in the db
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  stag-storenode.pl -d 'dbi:Pg:mydb' data.mog.xml

You generally don't need extra metadata here; everything can be
infered by introspecting the database.

If this works, you should now be able to retreive XML from the database, eg

  selectall_xml.pl -d 'dbi:Pg:mydb' 'SELECT * FROM x NATURAL JOIN y'