[help-GIFT] Understanding MRML

[Ralf Juengling]

Hi GIFT maintainers,

I would like to ask some questions about the MRML protocol; Wolfgang
encouraged me to post them to this list...
I found it hard to understand the protocol merely by reading your '99 TR
and still have quite a couple of questions. (I'll state them in several
postings since they are not highly related to each other...)

At first, I shall outline my rough understanding of some points; please
correct me if I'm wrong in what follows:
Since MRML messages are not validated, the DTD is to be taken as a
documentation of the protocol. In the TR you speak of an "MRML 
standard" which is a minimal set of tags and attributes, clients
and servers are supposed to use and understand respectively. 

Introducing new tags and attributes to support new functionality is
encouraged by the MRML inventors. GIFT itself uses many "non-standard
tags" which are flagged by th "cui-" prefix. Is the set of 
non-standard tags used by GIFT an "extension" of MRML? If so, why
isn't it treated this way, i.e. described by a document at
http://www.mrml.net/extensions ?

I feel some things were left unspecified, which should be to ensure 
interoparability. Let's consider for instance the value of the "type"
attribute of the "query-paradigm" tag. Besides its use in determining
which collections can be queried by which "algorithms", the tag-name
suggests, that it determines the *kind of query* (supported by the
query engine/algorithm, the client respectively). Thus, as I understand
it, the legal values of the "type" attribute should be specified by the
MRML protocol.
Think for instance of a the two classical query schemes "query by
keyword" vs "query by example". I can imagine an MRML-compliant client
which is supposed to merely support keyword queries. When it connects
to a CBIRS which on the other hand merely supports QBE, it should be
able to recognize that no queries can be made. 
If this isn't determined by the "query-paradigm" elements, what is
the way to go?

Thanks,
have a nice day,
Ralf

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Ralf Jüngling
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