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+=head1 NAME
+
+DBD::File::HowTo - Guide to create DBD::File based driver
+
+=head1 SYNOPSIS
+
+  perldoc DBD::File::HowTo
+  perldoc DBI
+  perldoc DBI::DBD
+  perldoc DBD::File::Developers
+  perldoc DBI::DBD::SqlEngine::Developers
+  perldoc DBI::DBD::SqlEngine
+  perldoc SQL::Eval
+  perldoc DBI::DBD::SqlEngine::HowTo
+  perldoc SQL::Statement::Embed
+  perldoc DBD::File
+  perldoc DBD::File::HowTo
+  perldoc DBD::File::Developers
+
+=head1 DESCRIPTION
+
+This document provides a step-by-step guide, how to create a new
+C<DBD::File> based DBD. It expects that you carefully read the L<DBI>
+documentation and that you're familiar with L<DBI::DBD> and had read and
+understood L<DBD::ExampleP>.
+
+This document addresses experienced developers who are really sure that
+they need to invest time when writing a new DBI Driver. Writing a DBI
+Driver is neither a weekend project nor an easy job for hobby coders
+after work. Expect one or two man-month of time for the first start.
+
+Those who are still reading, should be able to sing the rules of
+L<DBI::DBD/CREATING A NEW DRIVER>.
+
+Of course, DBD::File is a DBI::DBD::SqlEngine and you surely read
+L<DBI::DBD::SqlEngine::HowTo> before continuing here.
+
+=head1 CREATING DRIVER CLASSES
+
+Do you have an entry in DBI's DBD registry? For this guide, a prefix of
+C<foo_> is assumed.
+
+=head2 Sample Skeleton
+
+    package DBD::Foo;
+
+    use strict;
+    use warnings;
+    use vars qw(@ISA $VERSION);
+    use base qw(DBD::File);
+
+    use DBI ();
+
+    $VERSION = "0.001";
+
+    package DBD::Foo::dr;
+
+    use vars qw(@ISA $imp_data_size);
+
+    @ISA = qw(DBD::File::dr);
+    $imp_data_size = 0;
+
+    package DBD::Foo::db;
+
+    use vars qw(@ISA $imp_data_size);
+
+    @ISA = qw(DBD::File::db);
+    $imp_data_size = 0;
+
+    package DBD::Foo::st;
+
+    use vars qw(@ISA $imp_data_size);
+
+    @ISA = qw(DBD::File::st);
+    $imp_data_size = 0;
+
+    package DBD::Foo::Statement;
+
+    use vars qw(@ISA);
+
+    @ISA = qw(DBD::File::Statement);
+
+    package DBD::Foo::Table;
+
+    use vars qw(@ISA);
+
+    @ISA = qw(DBD::File::Table);
+
+    1;
+
+Tiny, eh? And all you have now is a DBD named foo which will is able to
+deal with temporary tables, as long as you use L<SQL::Statement>. In
+L<DBI::SQL::Nano> environments, this DBD can do nothing.
+
+=head2 Start over
+
+Based on L<DBI::DBD::SqlEngine::HowTo>, we're now having a driver which
+could do basic things. Of course, it should now derive from DBD::File
+instead of DBI::DBD::SqlEngine, shouldn't it?
+
+DBD::File extends DBI::DBD::SqlEngine to deal with any kind of files.
+In principle, the only extensions required are to the table class:
+
+    package DBD::Foo::Table;
+
+    sub bootstrap_table_meta
+    {
+	my ( $self, $dbh, $meta, $table ) = @_;
+
+	# initialize all $meta attributes which might be relevant for
+	# file2table
+
+	return $self->SUPER::bootstrap_table_meta($dbh, $meta, $table);
+    }
+
+    sub init_table_meta
+    {
+	my ( $self, $dbh, $meta, $table ) = @_;
+
+	# called after $meta contains the results from file2table
+	# initialize all missing $meta attributes
+
+	$self->SUPER::init_table_meta( $dbh, $meta, $table );
+    }
+
+In case C<DBD::File::Table::open_file> doesn't open the files as the driver
+needs that, override it!
+
+    sub open_file
+    {
+	my ( $self, $meta, $attrs, $flags ) = @_;
+	# ensure that $meta->{f_dontopen} is set
+	$self->SUPER::open_file( $meta, $attrs, $flags );
+	# now do what ever needs to be done
+    }
+
+Combined with the methods implemented using the L<SQL::Statement::Embed>
+guide, the table is full working and you could try a start over.
+
+=head2 User comfort
+
+C<DBD::File> since C<0.39> consolidates all persistent meta data of a table
+into a single structure stored in C<< $dbh->{f_meta} >>. While DBD::File
+provides only readonly access to this structure, modifications are still
+allowed.
+
+Primarily DBD::File provides access via setters C<get_file_meta>,
+C<set_file_meta> and C<clear_file_meta>. Those methods are easily
+accessible by the users via the C<< $dbh->func () >> interface provided
+by DBI. Well, many users don't feel comfortize when calling
+
+    # don't require extension for tables cars
+    $dbh->func ("cars", "f_ext", ".csv", "set_file_meta");
+
+DBD::File will inject a method into your driver to increase the user
+comfort to allow:
+
+    # don't require extension for tables cars
+    $dbh->foo_set_meta ("cars", "f_ext", ".csv");
+
+Better, but here and there users likes to do:
+
+    # don't require extension for tables cars
+    $dbh->{foo_tables}->{cars}->{f_ext} = ".csv";
+
+This interface is provided when derived DBD's define following in
+C<init_valid_attributes> (please compare carefully with the example in
+DBI::DBD::SqlEngine::HowTo):
+
+    sub init_valid_attributes
+    {
+	my $dbh = $_[0];
+
+	$dbh->SUPER::init_valid_attributes ();
+
+	$dbh->{foo_valid_attrs} = {
+	    foo_version 	=> 1,	# contains version of this driver
+	    foo_valid_attrs	=> 1,	# contains the valid attributes of foo drivers
+	    foo_readonly_attrs	=> 1,	# contains immutable attributes of foo drivers
+	    foo_bar		=> 1,	# contains the bar attribute
+	    foo_baz		=> 1,   # contains the baz attribute
+	    foo_manager		=> 1,	# contains the manager of the driver instance
+	    foo_manager_type	=> 1,	# contains the manager class of the driver instance
+	    foo_meta            => 1,   # contains the public interface to modify table meta attributes
+	};
+	$dbh->{foo_readonly_attrs} = {
+	    foo_version 	=> 1,	# ensure no-one modifies the driver version
+	    foo_valid_attrs	=> 1,	# do not permit to add more valid attributes ...
+	    foo_readonly_attrs	=> 1,	# ... or make the immutable mutable
+	    foo_manager		=> 1,	# manager is set internally only
+	    foo_meta            => 1,   # ensure public interface to modify table meta attributes are immutable
+	};
+
+	$dbh->{foo_meta} = "foo_tables";
+
+	return $dbh;
+    }
+
+This provides a tied hash in C<< $dbh->{foo_tables} >> and a tied hash for
+each table's meta data in C<< $dbh->{foo_tables}->{$table_name} >>.
+Modifications on the table meta attributes are done using the table
+methods:
+
+    sub get_table_meta_attr { ... }
+    sub set_table_meta_attr { ... }
+
+Both methods can adjust the attribute name for compatibility reasons, e.g.
+when former versions of the DBD allowed different names to be used for the
+same flag:
+
+    my %compat_map = (
+		       abc => 'foo_abc',
+		       xyz => 'foo_xyz',
+		     );
+    __PACKAGE__->register_compat_map( \%compat_map );
+
+If any user modification on a meta attribute needs reinitialization of
+the meta structure (in case of C<DBD::File> these are the attributes
+C<f_file>, C<f_dir>, C<f_ext> and C<f_lockfile>), inform DBD::File by
+doing 
+
+    my %reset_on_modify = (
+			    foo_xyz => "foo_bar",
+			    foo_abc => "foo_bar",
+			  );
+    __PACKAGE__->register_reset_on_modify( \%reset_on_modify );
+
+The next access to the table meta data will force DBD::File to re-do the
+entire meta initialization process.
+
+Any further action which needs to be taken can handled in
+C<table_meta_attr_changed>:
+
+    sub table_meta_attr_changed
+    {
+	my ($class, $meta, $attrib, $value) = @_;
+	...
+	$class->SUPER::table_meta_attr_changed ($meta, $attrib, $value);
+    }
+
+This is done before the new value is set in C<$meta>, so the attribute
+changed handler can act depending on the old value.
+
+=head2 Testing
+
+Now you should have your own DBD::File based driver. Was easy, wasn't it?
+But does it work well?  Prove it by writing tests and remember to use
+dbd_edit_mm_attribs from L<DBI::DBD> to ensure testing even rare cases.
+
+=head1 AUTHOR
+
+This guide is written by Jens Rehsack. DBD::File is written by Jochen
+Wiedmann and Jeff Zucker.
+
+The module DBD::File is currently maintained by
+
+H.Merijn Brand < h.m.brand at xs4all.nl > and
+Jens Rehsack  < rehsack at googlemail.com >
+
+=head1 COPYRIGHT AND LICENSE
+
+Copyright (C) 2010 by H.Merijn Brand & Jens Rehsack
+
+All rights reserved.
+
+You may freely distribute and/or modify this module under the terms of
+either the GNU General Public License (GPL) or the Artistic License, as
+specified in the Perl README file.
+
+=cut