XMLFilter chaining question...

[G. Todd Miller - XML Tech Ctr - Development]

Question: In the sample program UseXMLFilters.java (located in 
 xml-xalan/java/samples/UseXMLFilters) it appears that 3 XMLFilters
 (filter1, filter2, and filter3 in diagram) are being chained together
 into a pipeline, a Serializer is plugged into filter3 as a
 ContentHandler, and an XMLReader is plugged into filter1 as a parent.
 And then, the input XML document is being feed into the *last*
 filter in the pipeline:


  XMLReader       foo1.xsl   foo2.xsl   foo3.xsl          foo.xml
   |   ^             |          |         |                |
   |   |             |          |         |                |
   |   |             v          v         v                |
   |   |  xml   +----------+----------+-----------+  xml   |
   |   +----<---|          |          |           |<-------+
   |            | filter1  |  filter2 |  filter3  |
   +----->------|          |          |           |------> Serializer
   sax evts     +----------+----------+-----------+

 So the app program calls filter3.parse("foo.xml"); filter3 turns around
 and calls filter2.parse("foo.xml"); filter2 turns around and calls
 filter1.parse("foo.xml"); filter1 finally hands off the xml doc to
 an XMLReader, the reader parses the doc and produces SAX parser
 events. The parser events are input to filter1; transformed; output
 of transform is sent to filter2; transformed; output to filter3
 transformed and then output to Serializer.

 (If I am correct in this analysis) then the question: why have the
 Xml input doc be 'forwarded' from the end of the pipe to the beginning,
 to be read?   Why not design the pipeline such as:
 

                 foo1.xsl   foo2.xsl   foo3.xsl   
   foo.xml           |          |         |      
      |              |          |         |      
      |              v          v         v
      |         +----------+----------+-----------+ 
      v         |          |          |           |
  XMLReader---->| filter1  |  filter2 |  filter3  |------> Serializer
                |          |          |           |
                +----------+----------+-----------+


Thanks for any insights/corrections to this,

-Todd


=======================================================================
G. Todd Miller                        Sun Microsystems Computer Company
Software Systems Engineer             2 Network Drive, MS UBUR02-201
GE&IS XML Tech Center                 Burlington, MA 01803-0903
                                      781 442-0176
                                      781 442-1437 (fax)
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