----- Hans-Juergen says
This unease I immediately share when remembering the fact that in spite of the huge merits of XML technology, it seems almost always out
of the questions to migrate large-scale enterprise data from relational databases to XML. Is this not exactly because XML is too resource-centric in order to provide the fluid interconnectedness which relational databases after all provide?
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I am not sure where you get this opinion. This is done all the time. There are many installations of hundred-terrabyte to petabyte
scale
data collections entirely in XML that either came from Relational DB's at some point or could never be modeled in relational DB's to
begin with.
To *access* this data efficiently you need an XML Database ... or atleast a system with indexing built on top, but you needed that
with RDBMS's.
And the data model that works better with XML tends to be a De-Normalized model , the opposite of that of RDBMS's .. the translation
is usually smooth. Now there are certian "types" of data which RDBMS's tend to be more efficient or "natural" at storing, and some "types" of data that say a Triple store (aka RDF) is more natural. but I wouldn't use the term "large-scale enterprise data"
to be one of the characteristics
that is an indicator of whether Relational or XML databases or RDF are the better model. They all have unique limitations and strengths,
and IMHO it is generally the database engine itself which is the greatest differentiator. Although XML, specifically because of its
resource-centric data model does open types of large (shall I say "Big Data") scaling precisely because data is more localized within a single resource. This allows less number of coupled operations to be required to fetch or store the same amount of information
as in a normalized relational model.
So while there is a cognitive weakness in the resource model of XML there is also strength.
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David A. Lee
