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On Dec 23, 2003, at 7:48 AM, Qiang Song wrote:
> I am
> still not very clear about the raw storage form for XML
> documents.is it in pure text format?If true,how to execute the query
> and
> update operations.how to index for documents.if using DOM to build a
> tree
> from pure-text XML document before executing query or update,then i
> think
> it will be very low-efficiency.
>
I'd just echo what Michael Kay said -- doing this well is hard, and the
companies who work in this area generally do not say much about their
internal technologies. The point of "native XML" databases is NOT that
the data is stored internally in a standard XML text or Infoset/DOM
format, but that one uses XML interfaces such as DTDs/Schemas,
XPath/XQuery, and SAX/DOM to interact with the DB *as if* it were just
a huge text file or DOM tree.
For details on how people have addressed these challenges, you should
probably look at the open source NXDs such as Apache Xindice, dbXML,
and Sleepycat.
Ultimately, each implementation makes engineering tradeoffs that make
their approach more or less optimal for small vs large quantities of
data, large documents or small documents, XML representing unstructured
documents or structured data, optimized for reading or optimized for
updating, etc. The only real way to determine whether a specific
product (and the technology it is built on) is suitable for a specific
application is to prototype it and run benchmarks with realistic data
in the actual hardware/software environment. Don't believe ANY
marketing or benchmarking about performance of NXDs vs one another or
vs alternatives until you verify it under the conditions that YOU
expect.
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