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Re: Some clarificatiosn -- RE: [Question] How to do incremental parsing?

On 05/07/2001 18:33:39 "Xu, Mousheng  (SEA)" wrote:

>* What is "persistent DOM"?

I brought this up, so I had better provide an answer.  DOM itself is a set of interfaces, so it says nothing about how the actual XML data is stored.  The first DOM implementations stored the parsed information in a tree in memory, which meant that the size was more or less limited by the physical memory of your computer.  A persistent DOM is one where the parsed information is stored in a database.  Calls to DOM methods then cause the required parts of that information to be paged into memory, in just the same way that JDBC/ODBC/ADO calls result in some of the information in your database being paged into memory.  The result is that a persistent DOM can be as big as your database allows (which is typically a lot more than your physical memory), but if you only need to touch part of that information, then only that part ever gets loaded into memory.

As I noted before, having to page from a database into memory can be slower than having the whole thing constantly in memory, but that's OK, because existing databases are fast enough to do serious enterprise processing with, so there is no reason why a persistent DOM should be any less capable of "fast enough" processing of large volumes of enterprise (or other) data.

Anthony B. Coates
(1) Content Distribution Architect - Project Gazelle
(2) Leader of XML Architecture & Design - Chief Technology Office
Reuters Plc, London.

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