Z39.50 and the Web
Breakout Session at July 2000 ZIG Meeting
Preliminary Agenda
Revised July 8
- Z39.50 URL definition: does it need revision; what functionality should it support?
-
Distributed directory of Z39.50 servers. See
ServerList DTD
-
Record Source Schema and related issues. (
Synopsis)
- GRS vs. XML
- how to import a GRS schema definition
-
grs capability to distinguish the cases of "element not there", "element empty", "element not requested", and
the "diagnostic", for which there are no xml analogies.
-
GRS-1 can carry metadata which does not pertain to the record as a static database object, but which relates
to the context of the query which retrieved it. The best example is probably the HitVector which identifies
the parts of a record which match a query. Together with the variant mechanism, this allows the client to
request only the parts of the record which match the query. If Z39.50 is to be used to search large full-text
documents or similar, this is an important feature.
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GRS-1 can be contrasted to XML in that GRS is a retrieval record syntax while XML is a generic document
format. As such GRS imposes more constraints on retrieval data than does XML. Some things that GRS-1 defines
at a structural level will require Profiling for XML. Without that profiling, clients applications will have
fewer options for analysing and re-using data from different applications. But by requiring "proifiling" we
lose much of what xml promises to begin with: interoperability, portability, off-the-shelf support, ...
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On the other hand, XML can associate Style Sheets with specific DTDs (and, presumably, with schemas). These
style sheets may be used to control the display of records in dynamic ways. In a sense this is fundamentally
different from the Z39.50 model, which talks about structured information and tries to allow client
applications to make the most possible sense to retrieved records. The objective is not necessarily to display
the data - in fact, Z39.50 says little or nothing about displaying data. The immediate presentation of
retrieval records to the user is one possible application, but not the only one. Others include updating local
databases (such as bibliographic catalogues or bibliographies), merging data from different sources to present
a single result set to the user (a primary objective of Z39.50). Style sheets that are oriented towards
display really offer little assistance here. It is essential that the underlying structure of the data is
constrained sufficiently that commonality of metadata elements may be recognised and dealt with. This doesn't
necessarily mean that XML is a bad thing, but if implementors jump into it carelessly, XML-structured records
will have little more application than SUTRS or HTML. If the ZIG is to embrace XML, then it must lay down the
ground rules for best practices, or else forfeit a good 50% of what makes Z39.50 universally useful in the
first place (structured retrieval).
- Z39.50 Transport. TCP? HTTP? SOAP?
- XML Query
- RDF