NAME

       XML::Filter::Sort::BufferMgr - Implementation class used by XML::Filter::Sort

DESCRIPTION

       The documentation is targetted at developers wishing to extend or replace this class.  For
       user documentation, see XML::Filter::Sort.

       Two classes are used to implement buffering records and spooling them back out in sorted
       order as SAX events.  One instance of the XML::Filter::Sort::Buffer class is used to
       buffer each record and one or more instances of the XML::Filter::Sort::BufferMgr class are
       used to manage the buffers.

API METHODS

       The API of this module as used by XML::Filter::Sort::Buffer consists of the following
       sequence of method calls:

       1.  When the first 'record' in a sequence is encountered, XML::Filter::Sort creates a
           XML::Filter::Sort::BufferMgr object using the "new()" method.

       2.  XML::Filter::Sort calls the buffer manager's "new_buffer()" method to get a
           XML::Filter::Sort::Buffer object and all SAX events are directed to this object until
           the end of the record is encountered.  The following events are supported by the
           current buffer implementation:

             start_element()
             characters()
             comment()
             processing_instruction()
             end_element()

       3.  When the end of the record is detected, XML::Filter::Sort calls the buffer manager's
           "close_buffer()" method, which in turn calls the buffer's "close()" method.  The
           "close()" method returns a list of values for the sort keys and the buffer manager
           uses these to store the buffer for later recall.  Subsequent records are handled as
           per step 2.

       4.  When the last record has been buffered, XML::Filter::Sort calls the buffer manager's
           "to_sax()" method.  The buffer manager retrieves each of the buffers in sorted order
           and calls the buffer's "to_sax()" method.

       Each buffer attempts to match the sort key paths as SAX events are received.  Once a value
       has been found for a given key, that same path match is not attempted against subsequent
       events.  For efficiency, the code to match each key is compiled into a closure.  For even
       more efficiency, this compilation is done once when the XML::Filter::Sort object is
       created.  The "compile_matches()" method in the buffer manager class calls the
       "compile_matches()" method in the buffer class to achieve this.

DATA STRUCTURES

       In the current implementation, the XML::Filter::Sort::BufferMgr class simply uses a hash
       to store the buffer objects.  If only one sort key was defined, only a single hash is
       required.  The values in the hash are arrayrefs containing the list of buffers for records
       with identical keys.

       If two or more sort keys are defined, the hash values will be XML::Filter::Sort::BufferMgr
       objects which in turn will contain the buffers.  The following illustration may clarify
       the relationship (BM=buffer manager, B=buffer):

                                        BM
                        +----------------+---------------+
                        |                                |
                       BM                               BM
                  +-----+--------+                 +-----+----------+
                  |              |                 |                |
                 BM             BM                BM               BM
            +-----+----+    +----+------+     +----+----+    +------+------+
            |     |    |    |    |      |     |    |    |    |      |      |
         [B,B,B] [B] [B,B] [B] [B,B] [B,B,B] [B] [B,B] [B] [B,B] [B,B,B] [B,B]

       This layered storage structure is transparent to the XML::Filter::Sort object which
       instantiates and interacts with only one buffer manager (the one at the top of the tree).

COPYRIGHT

       Copyright 2002 Grant McLean <grantm@cpan.org>

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.