[DAS] Re: RFC DAS-Headers

[Lincoln Stein]

(I know I'm replying late to this, but I'm chronically trying to catch
up on backlogged e-mail)

Brian, Matthew,

I've run into exactly this problem myself with DAS/1.  The parser has
to read into the XML a bit until it gets to the first tag, and then
configure itself to read the rest of the document.  A little
inconvenient, but it doesn't seem to add that much overhead.  

Two comments:

  1) Adding new HTTP headers seems an un-SOAPish way to identify the
     payload.  The SOAP headers and envelope are supposed to do this.

  2) The client ought to be able to ask the server for the schema that
     it wants.  When the two connect, there should be a service
     discovery in which the two exchange capabilities documents.

So do we really need schema discovery at the time of document
transmittal, or should this be moved to an earlier phase?

Lincoln

Brian Gilman writes:
 > Yes but you need to instantiate a parser to parse the document. It would
 > be better to know the doctype upfront and then instantiate your parser
 > (Doc handler). I don't want to have to chain together a bunch of doc
 > handlers to get to the right paring facility. If we put this stuff in then
 > header then all we have to do is read this and instantiate the right
 > parser at runtime. 
 > 	
 > 	We put this information in our DASMetaData object in OmniDAS and
 > pull it out when we parse documents to eventually bind to objects. This
 > makes our life very easy and frees us up to do other more interesting work
 > down stream. 
 > 
 > 
 > 			-B
 > 
 > -----------------------
 > Brian Gilman <gilmanb@genome.wi.mit.edu>
 > Sr. Software Engineer MIT/Whitehead Inst. Center for Genome Research
 > One Kendall Square, Bldg. 300 / Cambridge, MA 02139-1561 USA
 > phone +1 617  252 1069 / fax +1 617 252 1902
 > 
 > 
 > On Tue, 13 Nov 2001, Matthew Pocock wrote:
 > 
 > > Hi Brian,
 > > 
 > > Shouldn't the XML document tell you this info already in the doctype 
 > > declaration?
 > > 
 > > Matthew
 > > 
 > > Brian Gilman wrote:
 > > 
 > > > DAS transmits data through HTTP and XML. Specifically, DAS transmits data
 > > > using the GFF XML schema. This schema may not suit all DAS users needs and
 > > > may be better served by another XML schema. Therefore, I propose adding
 > > > two new headers to the output of a DAS server whether it is DAS 1.0 or DAS
 > > > 2.0. 
 > > > 
 > > > 	X-DAS-SchemaName --> The name of the DTD which is used for
 > > > encoding encoded as a URL
 > > > 
 > > > 	X-DAS-SchemaVersion --> The version in the form of x.xx
 > > > 
 > > > 	This will allow applications to dynamically instantiate a parser
 > > > for the DTD instance document which is being transmitted and not tether
 > > > users of DAS to a particular DTD. 
 > > > 
 > > > 			-B
 > > > 
 > > > -----------------------
 > > > Brian Gilman <gilmanb@genome.wi.mit.edu>
 > > > Sr. Software Engineer MIT/Whitehead Inst. Center for Genome Research
 > > > One Kendall Square, Bldg. 300 / Cambridge, MA 02139-1561 USA
 > > > phone +1 617  252 1069 / fax +1 617 252 1902
 > > > 
 > > > 
 > > > 
 > > 
 > > 
 > > 
 > > 

-- 
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Lincoln D. Stein                           Cold Spring Harbor Laboratory
lstein@cshl.org			                  Cold Spring Harbor, NY

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