[XML4LIB] Databases or XML

Andrea Giuliano a.giuliano at iccu.sbn.it
Tue Feb 12 12:38:36 EST 2002


A. Bullen wrote:

 >Dear all,
 >
 >At the urging of Roy Tennant, I am asking you all the same question that
 >I asked him.
 >
 >Please pardon a rather naive question. I am a database programmer; that
 >is, I put library SQL/ODBC connected databases on Internet-accesible
 >platforms and build Web interfaces to them using Perl and Java. I have,
 >of course, heard a great deal about XML and the revolution in
 >information presentation. My question to use is: why do I need to work
 >in XML when I can do everything in a sense better by using a database? I
 >can replace XSLT/DTDs etc. with server side includes that detect browser
 >types, and present the screen to the client accordingly by having a
 >series of if/then statements in my presentation code. In short, I can
 >build dynamically presented pages 'til the cows come home. What am I
 >missing?
 >
 >I appreciate any comments or thoughts you might have on my dilemna.
 >
 >Sincerely,
 >Andrew Bullen
 >Illinois State Library
 >
Dear Andrew,

as someone already pointed out on the list, XML is a good choice to
exchange data between application, because of the tree structure of an
XML document, a very versatile data structure. But, from a mathematical
point of view, relational databases are graphs, and trees are just a
very particular kind of graphs. So every tree is itself a graph but, on
the other hand, not evey graph can be arranged as a tree. So you can run
across a database which cannot be arranged as a tree, whatever you do.

XML has the ID-IDREF feature to give a document a graph structure,
creating links between nodes that are on different branches of the tree
(just like symbolic links in UNIX filesystem). But I have not a good
practice with such a feature, except for DocBook documents, not a good
example when speaking of databases. Though, it could be a way to map a
database in a XML document .

Anyway, I think the only reason to do this is to serialize part of the
content of a database in order to upload this content in another
database, maybe much different from the source. In this respect, clearly
XML is an alternative to MARC formats.

Best regards.

-- 
(To reply to this message, remove ".abc" from the address)

Andrea Giuliano, Ph. D.
Virtual System Administrator
ICCU - Istituto Centrale per il Catalogo Unico
Viale Castro Pretorio 105, Rome - ITALY
Tel. +39064989509, Fax +39064059302





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