stag-storenodep - Online in the Cloud

PROGRAM:

NAME

stag-storenode.pl - script is for storing data in database

SYNOPSIS

stag-storenode.pl -d "dbi:Pg:dbname=mydb;host=localhost" myfile.xml

DESCRIPTION

This script is for storing data (specified in a nested file format such as XML or
S-Expressions) in a database. It assumes a database schema corresponding to the tags in
the input data already exists.

ARGUMENTS
-d DBNAME

This is either a DBI locator or the logical name of a database in the DBSTAG_DBIMAP_FILE
config file

-user USER

db user name

-password PASSWORD

db user password

-u UNIT

This is the node/element name on which to load; a database loading event will be fired
every time one of these elements is parsed; this also constitutes a whole transaction

-c STAGMAPFILE

This is a stag mapping file, indicating which elements are aliases

-p PARSER

Default is xml; can be any stag compatible parser, OR a perl module which will parse the
input file and fire stag events (see Data::Stag::BaseGenerator)

-t TRANSFORMER

This is the name of a perl module that will perform a transformation on the stag
events/XML. See also stag-handle.pl

-noupdate NODELIST

A comma-seperated (no spaces) list of nodes/elements on which no update should be
performed if a unique key is found to be present in the DB

-trust_ids

If this flag is present, the values for primary key values are trusted; otherwise they are
assumed to be surrogate internal IDs that should not be used. In this case they will be
remapped.

-tracenode TABLE/COLUMN

E.g.

-tracenode person/name

Writes out a line on STDERR for every new person inserted/updated

-cache TABLE=MODE

Can be specified multiple times

Example:

-cache

0: off (default)
1: memory-caching ON
2: memory-caching OFF, bulkload ON
3: memory-caching ON, bulkload ON

IN-MEMORY CACHING

By default no in-memory caching is used. If this is set to 1, then an in-memory cache is
used for any particular element. No cache management is used, so you should be sure not to
cache elements that will cause memory overloads.

Setting this will not affect the final result, it is purely an efficiency measure for use
with storenode().

The cache is indexed by all unique keys for that particular element/table, wherever those
unique keys are set

BULKLOAD

If bulkload is used without memory-caching (set to 2), then only INSERTs will be performed
for this element. Note that this could potentially cause a unique key violation, if the
same element is present twice

If bulkload is used with memory-caching (set to 3) then only INSERTs will be performed;
the unique serial/autoincrement identifiers for those inserts will be cached and used.
This means you can have the same element twice. However, the load must take place in one
session, otherwise the contents of memory will be lost

XML TO DB MAPPING

See DBIx::DBStag for details of the actual mapping. Two styles of mapping are allowed:
stag-dbxml and XORT-style XML. You do not have to specify which, they are sufficiently
similar that the loader can accept either.

MAKING DATABASE FROM XML FILES

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 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 -u movie -d 'dbi:Pg:mydb' data.mog.xml

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

The -u|unit switch controls when transactions are committed

You can omit the -u switch, and every node directly under the top node will be stored.
This will also be the transaction unit.

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

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

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