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I suspect your estimate is as close as any, that there are few , percentage-wise, installations of enterprise XML data stores, compared to relational ... but this has nothing to do with XML (IMHO). It has to do with the head-start in time (30 years ?) relational DBs have over XML Databases.
At one point Oracle was a small company too ... It also has to do with the fact that XML is useful *without* a database whereas relational data is practically useless without a database. So the wall you hit with usefulness using data without a database is hit much sooner with relational data then with XML so the only place you see
relational data is in a database. So yes most enterprise databases (and non-enterprise databases) are RDBMS today.
But XML *is* in very large enterprise data centers and works very well there.
So I disagree with the assertion that its
" almost always out of the questions to migrate large-scale enterprise data from relational databases to XML" If it is out of the question its an install base or educational (we already own / hired RDBMS xxx) issue not a technical one. From: Hans-Juergen Rennau [mailto:hrennau@yahoo.de]
David, Von: David Lee <dlee@calldei.com> ----- 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?
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.
---------------------------------------- David A. Lee
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