Provided by: libdbix-dbstag-perl_0.12-1_all 
NAME
DBIx::DBStag - Relational Database to Hierarchical (Stag/XML) Mapping
SYNOPSIS
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'
USE NESTING
(set(studio(movie(star))))
];
my $dataset = $dbh->selectall_stag($sql);
my @studios = $dataset->get_studio;
# returns nested data that looks like this -
#
# (studio
# (name "20th C Fox")
# (movie
# (name "star wars") (genre "sci-fi")
# (star
# (firstname "Carrie")(lastname "Fisher")))))
# iterate through result tree -
foreach my $studio (@studios) {
printf "STUDIO: %s\n", $studio->get_name;
my @movies = $studio->get_movie;
foreach my $movie (@movies) {
printf " MOVIE: %s (genre:%s)\n",
$movie->get_name, $movie->get_genre;
my @stars = $movie->get_star;
foreach my $star (@stars) {
printf " STARRING: %s:%s\n",
$star->get_firstname, $star->get_lastname;
}
}
}
# manipulate data then store it back in the database
my @allstars = $dataset->get("movie/studio/star");
$_->set_fullname($_->get_firstname.' '.$_->get_lastname)
foreach(@allstars);
$dbh->storenode($dataset);
exit 0;
Or from the command line:
unix> selectall_xml.pl -d 'dbi:Pg:dbname=moviebase' \
'SELECT * FROM studio NATURAL JOIN movie NATURAL \
JOIN movie_to_star NATURAL JOIN star \
USE NESTING (set(studio(movie(star))))'
Or using a predefined template:
unix> selectall_xml.pl -d moviebase /mdb-movie genre=sci-fi
DESCRIPTION
This module is for mapping between relational databases and Stag objects (Structured Tags - see
Data::Stag). Stag objects can also be represented as XML. The module has two main uses:
Querying
This module can take the results of any SQL query and decompose the flattened results into a tree
data structure which reflects the foreign keys in the underlying relational schema. It does this by
looking at the SQL query and introspecting the database schema, rather than requiring metadata or an
object model.
In this respect, the module works just like a regular DBI handle, with a few extra methods.
Queries can also make use of predefined templates
Storing Data
DBStag objects can store any tree-like datastructure (such as XML documents) into a database using
normalized schema that reflects the structure of the tree being stored. This is done using little or
no metadata.
XML can also be imported, and a relational schema automatically generated.
For a tutorial on using DBStag to build and query relational databases from XML sources, please see
DBIx::DBStag::Cookbook
HOW QUERY RESULTS ARE TURNED INTO STAG/XML
This is a general overview of the rules for turning SQL query results into a tree like data structure.
You don't need to understand all these rules to be able to use this module - you can experiment by using
the selectall_xml.pl script which comes with this distribution.
Mapping Relations
Relations (i.e. tables and views) are elements (nodes) in the tree. The elements have the same name as
the relation in the database.
These nodes are always non-terminal (ie they always have child nodes)
Mapping Columns
Table and view columns of a relation are sub-elements of the table or view to which they belong. These
elements will be data elements (i.e. terminal nodes). Only the columns selected in the SQL query will be
present.
For example, the following query
SELECT name, job FROM person;
will return a data structure that looks like this:
(set
(person
(name "fred")
(job "forklift driver"))
(person
(name "joe")
(job "steamroller mechanic")))
The data is shown as a lisp-style S-Expression - it can also be expressed as XML, or manipulated as an
object within perl.
Handling table aliases
If an ALIAS is used in the FROM part of the SQL query, the relation element will be nested inside an
element with the same name as the alias. For instance, the query
SELECT name FROM person AS author WHERE job = 'author';
Will return a data structure like this:
(set
(author
(person
(name "Philip K Dick"))))
The underlying assumption is that aliasing is used for a purpose in the original query; for instance, to
determine the context of the relation where it may be ambiguous.
SELECT *
FROM person AS employee
INNER JOIN
person AS boss ON (employee.boss_id = boss.person_id)
Will generate a nested result structure similar to this -
(set
(employee
(person
(person_id "...")
(name "...")
(salary "...")
(boss
(person
(person_id "...")
(name "...")
(salary "..."))))))
If we neglected the alias, we would have 'person' directly nested under 'person', and the meaning would
not be obvious. Note how the contents of the SQL query dynamically modifies the schema/structure of the
result tree.
NOTE ON SQL SYNTAX
Right now, DBStag is fussy about how you specify aliases; you must use AS - you must say
SELECT name FROM person AS author;
instead of
SELECT name FROM person author;
Nesting of relations
The main utility of querying using this module is in retrieving the nested relation elements from the
flattened query results. Given a query over relations A, B, C, D,... there are a number of possible tree
structures. Not all of the tree structures are meaningful or useful.
Usually it will make no sense to nest A under B if there is no foreign key relationship linking either A
to B, or B to A. This is not always the case - it may be desirable to nest A under B if there is an
intermediate linking table that is required at the relational level but not required in the tree
structure.
DBStag will guess a structure/schema based on the ordering of the relations in your FROM clause. However,
this guess can be over-ridden at either the SQL level (using DBStag specific SQL extensions) or at the
API level.
The default algorithm is to nest each relation element under the relation element preceding it in the
FROM clause; for instance:
SELECT * FROM a NATURAL JOIN b NATURAL JOIN c
If there are appropriately named foreign keys, the following data will be returned (assuming one column
'x_foo' in each of a, b and c)
(set
(a
(a_foo "...")
(b
(b_foo "...")
(c
(c_foo "...")))))
where 'x_foo' is a column in relation 'x'
This is not always desirable. If both b and c have foreign keys into table a, DBStag will not detect this
- you have to guide it. There are two ways of doing this - you can guide by bracketing your FROM clause
like this:
SELECT * FROM (a NATURAL JOIN b) NATURAL JOIN c
This will generate
(set
(a
(a_foo "...")
(b
(b_foo "..."))
(c
(c_foo "..."))))
Now b and c are siblings in the tree. The algorithm is similar to before: nest each relation element
under the relation element preceding it; or, if the preceding item in the FROM clause is a bracketed
structure, nest it under the first relational element in the bracketed structure.
(Note that in MySQL you may not place brackets in the FROM clause in this way)
Another way to achieve the same thing is to specify the desired tree structure using a DBStag specific
SQL extension. The DBStag specific component is removed from the SQL before being presented to the DBMS.
The extension is the USE NESTING clause, which should come at the end of the SQL query (and is
subsequently removed before processing by the DBMS).
SELECT *
FROM a NATURAL JOIN b NATURAL JOIN c
USE NESTING (set (a (b)(c)));
This will generate the same tree as above (i.e. 'b' and 'c' are siblings). Notice how the nesting in the
clause is the same as the nesting in the resulting tree structure.
Note that 'set' is not a table in the underlying relational schema - the result data tree requires a
named top level node to group all the 'a' relations under. You can call this top level element whatever
you like.
If you are using the DBStag API directly, you can pass in the nesting structure as an argument to the
select call; for instance:
my $xmlstr =
$dbh->selectall_xml(-sql=>q[SELECT *
FROM a NATURAL JOIN b
NATURAL JOIN c],
-nesting=>'(set (a (b)(c)))');
or the equivalent -
my $xmlstr =
$dbh->selectall_xml(q[SELECT *
FROM a NATURAL JOIN b
NATURAL JOIN c],
'(set (a (b)(c)))');
If you like, you can also use XML here (only at the API level, not at the SQL level) -
my $seq =
$dbh->selectall_xml(-sql=>q[SELECT *
FROM a NATURAL JOIN b
NATURAL JOIN c],
-nesting=>q[
<set>
<a>
<b></b>
<c></c>
</a>
</set>
]);
As you can see, this is a little more verbose than the S-Expression
Most command line scripts that use this module should allow pass-through via the '-nesting' switch.
Aliasing of functions and expressions
If you alias a function or an expression, DBStag needs to know where to put the resulting column; the
column must be aliased.
This is inferred from the first named column in the function or expression; for example, the SQL below
uses the minus function:
SELECT blah.*, foo.*, foo.x-foo.y AS z
The z element will be nested under the foo element
You can force different nesting using a double underscore:
SELECT blah.*, foo.*, foo.x - foo.y AS blah__z
This will nest the z element under the blah element
If you would like to override this behaviour and use the alias as the element name, pass in the
-aliaspolicy=>'a' arg to the API call. If you wish to use the table names without nesting, use
-aliaspolicy=>'t'.
Conformance to DTD/XML-Schema
DBStag returns Data::Stag structures that are equivalent to a simplified subset of XML (and also a
simplified subset of lisp S-Expressions).
These structures are examples of semi-structured data - a good reference is this book -
Data on the Web: From Relations to Semistructured Data and XML
Serge Abiteboul, Dan Suciu, Peter Buneman
Morgan Kaufmann; 1st edition (January 2000)
The schema for the resulting Stag structures can be seen to conform to a schema that is dynamically
determined at query-time from the underlying relational schema and from the specification of the query
itself.
If you need to generate a DTD you can ause the stag-autoschema.pl script, which is part of the Data::Stag
distribution
QUERY METHODS
The following methods are for using the DBStag API to query a database
connect
Usage - $dbh = DBIx::DBStag->connect($DSN);
Returns - L<DBIx::DBStag>
Args - see the connect() method in L<DBI>
This will be the first method you call to initiate a DBStag object
The DSN may be a standard DBI DSN, or it can be a DBStag alias
selectall_stag
Usage - $stag = $dbh->selectall_stag($sql);
$stag = $dbh->selectall_stag($sql, $nesting_clause);
$stag = $dbh->selectall_stag(-template=>$template,
-bind=>{%variable_bindinfs});
Returns - L<Data::Stag>
Args - sql string,
[nesting string],
[bind hashref],
[template DBIx::DBStag::SQLTemplate]
Executes a query and returns a Data::Stag structure
An optional nesting expression can be passed in to control how the relation is decomposed into a tree.
The nesting expression can be XML or an S-Expression; see above for details
selectall_xml
Usage - $xml = $dbh->selectall_xml($sql);
Returns - string
Args - See selectall_stag()
As selectall_stag(), but the results are transformed into an XML string
selectall_sxpr
Usage - $sxpr = $dbh->selectall_sxpr($sql);
Returns - string
Args - See selectall_stag()
As selectall_stag(), but the results are transformed into an S-Expression string; see Data::Stag for more
details.
selectall_sax
Usage - $dbh->selectall_sax(-sql=>$sql, -handler=>$sax_handler);
Returns - string
Args - sql string, [nesting string], handler SAX
As selectall_stag(), but the results are transformed into SAX events
[currently this is just a wrapper to selectall_xml but a genuine event generation model will later be
used]
selectall_rows
Usage - $tbl = $dbh->selectall_rows($sql);
Returns - arrayref of arrayref
Args - See selectall_stag()
As selectall_stag(), but the results of the SQL query are left undecomposed and unnested. The resulting
structure is just a flat table; the first row is the column headings. This is similar to
DBI->selectall_arrayref(). The main reason to use this over the direct DBI method is to take advantage of
other stag functionality, such as templates
prepare_stag PRIVATE METHOD
Usage - $prepare_h = $dbh->prepare_stag(-template=>$template);
Returns - hashref (see below)
Args - See selectall_stag()
Returns a hashref
{
sth=>$sth,
exec_args=>\@exec_args,
cols=>\@cols,
col_aliases_ordered=>\@col_aliases_ordered,
alias=>$aliasstruct,
nesting=>$nesting
};
STORAGE METHODS
The following methods are for using the DBStag API to store nested data in a database
storenode
Usage - $dbh->storenode($stag);
Returns -
Args - L<Data::Stag>
SEE ALSO: The stag-storenode.pl script
Recursively stores a stag tree structure in the database.
The database schema is introspected for most of the mapping data, but you can supply your own (see later)
The Stag tree/XML must be a direct mapping of the relational schema. Column and table names must
correspond to element names. Elements may be nested. Different styles of XML-Relational mapping may be
used: XORT-style and the more compact Stag-style
XORT-style mapping
With a XORT-style mapping, elements corresponding to tables can be nested under elements corresponding to
foreign keys.
For example, if the relational schema has a foreign key from table person to table address, the following
XML is permissable:
<person>
<name>..</name>
<address_id>
<address>
</address>
</address_id>
</person>
The address node will be stored in the database and collapsed to whatever the value of the primary key
is.
Stag-style mapping
Stag-style is more compact, but sometimes relies on the presence of a dbstag_metadata element to specify
how foreign keys are mapped
Operations
Operations are specified as attributes inside elements, specifying whether the nod should be inserted,
updated, looked up or stored/forced. Operations are optional (default is force/store).
<person op="insert">
<name>fred</name>
<address_id op="lookup">
<streetaddr>..</>
<city>..</>
</address_id>
</person>
The above will always insert into the person table (which may be quite dangerous; if an entry with the
same unique constraint exists, an error will be thrown). Assuming (streetaddr,city) is a unique
constraint for the address table, this will lookup the specified address (and not modify the table) and
use the returned pk value for the person.address_id foreign key
The operations are:
force (default)
looks up (by unique constraints) first; if exists, will do an update. if does not exist, will do an
insert
insert
insert only. DBMS will throw error if row with same UC exists
update
update only. DBMS will throw error if a row the with the specified UC cannot be found
lookup
finds the pk value using one of the unique constraints present in the XML node
delete NOT IMPLEMENTED
deletes row that has matching UC
Operations can be used in either XORT or Stag mode
Macros
Macros can be used with either XORT or Stag style mappings. Macros allow you to refer to the same node
later on in the XML
<person op="lookup" id="joe">
<name>joe</name>
</person>
<person op="lookup" id="fred">
<name>fred</name>
</person>
...
<person_relationship>
<type>friend</type>
<person1_id>joe</person1_id>
<person2_id>fred</person2_id>
</person_relationship>
Assuming name is a unique constraint for person, and person_relationship has two foreign keys named
person1_id and person2_id linking to the person table, DBStag will first lookup the two person rows by
name (throwing an error if not present) and use the returned pk values to populate the
person_relationship table
How it works
Before a node is stored, certain subnodes will be pre-stored; these are subnodes for which there is a
foreign key mapping FROM the parent node TO the child node. This pre-storage is recursive.
After these nodes are stored, the current node is either INSERTed or UPDATEd. The database is
introspected for UNIQUE constraints; these are used as keys. If there exists a row in the database with
matching key, then the node is UPDATEd; otherwise it is INSERTed.
(primary keys from pre-stored nodes become foreign key values in the existing node)
Subsequently, all subnodes that were not pre-stored are now post-stored. The primary key for the
existing node will become foreign keys for the post-stored subnodes.
force_safe_node_names
Usage - $dbh->force_safe_node_names(1);
Returns - bool
Args - bool [optional]
If this is set, then before storage, all node names are made DB-safe; they are lowercased, and the
following transform is applied:
tr/a-z0-9_//cd;
mapping
Usage - $dbh->mapping(["alias/table.col=fktable.fkcol"]);
Returns -
Args - array
Creates a stag-relational mapping (for storing data only)
Occasionally not enough information can be obtained from db introspection; you can provide extra mapping
data this way.
Occasionally you stag objects/data/XML will contain aliases that do not correspond to actual SQL
relations; the aliases are intermediate nodes that provide information on which foreign key column to use
For example, with data like this:
(person
(name "...")
(favourite_film
(film (....))
(least_favourite_film
(film (....)))))
There may only be two SQL tables: person and film; person would have two foreign key columns into film.
The mapping may look like this
["favourite_film/person.favourite_film_id=film.film_id",
"least_favourite_film/person.least_favourite_film_id=film.film_id"]
The mapping can also be supplied in the xml that is loaded; any node named "dbstag_metadata" will not be
loaded; it is used to supply the mapping. For example:
<personset>
<dbstag_mapping>
<map>favourite_film/person.favourite_film_id=film.film_id</map>
<map>least_favourite_film/person.least_favourite_film_id=film.film_id</map>
</dbstag_mapping>
<person>...
mapconf
Usage - $dbh->mapconf("mydb-stagmap.stm");
Returns -
Args - filename
sets the conf file containing the stag-relational mappings
This is not of any use for a XORT-style mapping, where foreign key columns are explicitly stated
See mapping() above
The file contains line like:
favourite_film/person.favourite_film_id=film.film_id
least_favourite_film/person.least_favourite_film_id=film.film_id
noupdate_h
Usage - $dbh->noupdate_h({person=>1})
Returns -
Args - hashref
Keys of hash are names of nodes that do not get updated - if a unique key is queried for and does not
exist, the node will be inserted and subnodes will be stored; if the unique key does exist in the db,
then this will not be updated; subnodes will not be stored
trust_primary_key_values
Usage - $dbh->trust_primary_key_values(1)
Returns - bool
Args - bool (optional)
The default behaviour of the storenode() method is to remap all surrogate PRIMARY KEY values it comes
across.
A surrogate primary key is typically a primary key of type SERIAL (or AUTO_INCREMENT) in MySQL. They are
identifiers assigned automatically be the database with no semantics.
It may be desirable to store the same data in two different databases. We would generally not expect the
surrogate IDs to match between databases, even if the rest of the data does.
(If you do not use surrogate primary key columns in your load xml, then you can ignore this accessor)
You should NOT use this method in conjunction with Macros
If you use primary key columns in your XML, and the primary keys are not surrogate, then youshould set
this. If this accessor is set to non-zero (true) then the primary key values in the XML will be used.
If your db has surrogate/auto-increment/serial PKs, and you wish to use these PK columns in your XML, yet
you want to make XML that can be exported from one db and imported into another, then the default
behaviour will be fine.
For example, if we extract a 'person' from a db with surrogate PK id and unique key ssno, we may get
this:
<person>
<id>23</id>
<name>fred</name>
<ssno>1234-567</ssno>
</person>
If we then import this into an entirely fresh db, with no rows in table person, then the default
behaviour of storenode() will create a row like this:
<person>
<id>1</id>
<name>fred</name>
<ssno>1234-567</ssno>
</person>
The PK val 23 has been mapped to 1 (all foreign keys that point to person.id=23 will now point to
person.id=1)
If we were to first call $sdbh->trust_primary_key_values(1), then person.id would remain to be 23. This
would only be appropriate behaviour if we were storing back into the same db we retrieved from.
tracenode
Usage - $dbh->tracenode('person/name')
Traces on STDERR inserts/updates on a particular element type (table), displaying the sub-element (column
value).
is_caching_on ADVANCED OPTION
Usage - $dbh->is_caching_on('person', 1)
Returns - number
Args - number
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
clear_cache
Usage - $dbh->clear_cache;
Returns -
Args - none
Clears the in-memory cache
Caches are not automatically managed - the API user is responsible for making suring the cache does not
get too big
cache_summary
Usage - print $dbh->cache_summary->xml
Returns - L<Data::Stag>
Args -
Gives a summary of the size of the in-memory cache by keys. This can be used for automatic cache
management:
$person_cache = $dbh->cache_summary->get_person;
my @index_nodes = $person_cache->tnodes;
foreach (@index_nodes) {
if ($_->data > MAX_PERSON_CACHE_SIZE) {
$dbh->clear_cache;
}
}
SQL TEMPLATES
DBStag comes with its own SQL templating system. This allows you to reuse the same canned SQL or similar
SQL qeuries in different contexts. See DBIx::DBStag::SQLTemplate
find_template
Usage - $template = $dbh->find_template("my-template-name");
Returns - L<DBIx::DBStag::SQLTemplate>
Args - str
Returns an object representing a canned paramterized SQL query. See DBIx::DBStag::SQLTemplate for
documentation on templates
list_templates
Usage - $templates = $dbh->list_templates();
Returns - Arrayref of L<DBIx::DBStag::SQLTemplate>
Args -
Returns a list of ALL defined templates - See DBIx::DBStag::SQLTemplate
find_templates_by_schema
Usage - $templates = $dbh->find_templates_by_schema($schema_name);
Returns - Arrayref of L<DBIx::DBStag::SQLTemplate>
Args - str
Returns a list of templates for a particular schema - See DBIx::DBStag::SQLTemplate
find_templates_by_dbname
Usage - $templates = $dbh->find_templates_by_dbname("mydb");
Returns - Arrayref of L<DBIx::DBStag::SQLTemplate>
Args - db name
Returns a list of templates for a particular db
Requires resources to be set up (see below)
RESOURCES
Generally when connecting to a database, it is necessary to specify a DBI style DSN locator. DBStag also
allows you specify a resource list file which maps logical names to full locators
The following methods allows you to use a resource list
resources_list
Usage - $rlist = $dbh->resources_list
Returns - arrayref to a hashref
Args - none
Returns a list of resources; each resource is a hash
{name=>"mydbname",
type=>"rdb",
schema=>"myschema",
}
SETTING UP RESOURCES
The above methods rely on you having a file describing all the relational dbs available to you, and
setting the env var DBSTAG_DBIMAP_FILE set (this is a : separated list of paths).
This is alpha code - not fully documented, API may change
Currently a resources file is a whitespace delimited text file - XML/Sxpr/IText definitions may be
available later
Here is an example of a resources file:
# LOCAL
mytestdb rdb Pg:mytestdb schema=test
# SYSTEM
worldfactbook rdb Pg:worldfactbook@db1.mycompany.com schema=wfb
employees rdb Pg:employees@db2.mycompany.com schema=employees
The first column is the nickname or logical name of the resource/db. This nickname can be used instead of
the full DBI locator path (eg you can just use employees instead of
dbi:Pg:dbname=employees;host=db2.mycompany.com
The second column is the resource type - rdb is for relational database. You can use the same file to
track other system datasources available to you, but DBStag is only interested in relational dbs.
The 3rd column is a way of locating the resource - driver:name@host
The 4th column is a ; separated list of tag=value pairs; the most important tag is the schema tag.
Multiple dbs may share the same schema, and hence share SQL Templates
COMMAND LINE SCRIPTS
DBStag is usable without writing any perl, you can use command line scripts and files that utilise tree
structures (XML, S-Expressions)
selectall_xml.pl
selectall_xml.pl -d <DSN> [-n <nestexpr>] <SQL>
Queries database and writes decomposed relation as XML
Can also be used with templates:
selectall_xml.pl -d <DSN> /<templatename> <var1> <var2> ... <varN>
selectall_html.pl
selectall_html.pl -d <DSN> [-n <nestexpr>] <SQL>
Queries database and writes decomposed relation as HTML with nested tables indicating the nested
structures.
stag-storenode.pl
stag-storenode.pl -d <DSN> <file>
Stores data from a file (Supported formats: XML, Sxpr, IText - see Data::Stag) in a normalized
database. Gets it right most of the time.
TODO - metadata help
stag-autoddl.pl
stag-autoddl.pl [-l <linktable>]* <file>
Takes data from a file (Supported formats: XML, Sxpr, IText - see Data::Stag) and generates a
relational schema in the form of SQL CREATE TABLE statements.
ENVIRONMENT VARIABLES
DBSTAG_TRACE
setting this environment will cause all SQL statements to be printed on STDERR, as well as a full
trace of how nodes are stored
BUGS
The SQL parsing can be quite particular - sometimes the SQL can be parsed by the DBMS but not by DBStag.
The error messages are not always helpful.
There are probably a few cases the SQL SELECT parsing grammar cannot deal with.
If you want to select from views, you need to hack DBIx::DBSchema (as of v0.21)
TODO
Use SQL::Translator to make SQL DDL generation less Pg-specific; also for deducing foreign keys (right
now foreign keys are guessed by the name of the column, eg table_id)
Can we cache the grammar so that startup is not so slow?
Improve algorithm so that events are fired rather than building up entire structure in-memory
Tie in all DBI attributes accessible by hash, i.e.: $dbh->{...}
Error handling
WEBSITE
<http://stag.sourceforge.net>
AUTHOR
Chris Mungall <cjm AT fruitfly DOT org>
COPYRIGHT
Copyright (c) 2004 Chris Mungall
This module is free software. You may distribute this module under the same terms as perl itself