Why XML Over the Relational Model?

Simon St.Laurent simonstl at simonstl.com
Sun Jan 3 16:51:55 GMT 1999

At 04:06 PM 1/2/99 -0600, len bullard wrote:
>The tutorial by example does raise the question often asked 
>and seldom answered by the XML community:  precisely 
>why should developers choose this approach (XML 
>and Java objects) over a commercial relational 
>database given the ease by which this example can be done 
>using standard SQL, script, and an  
>HTML browser?  As this same question occupied 
>many of the venerable CALS developers for some period, 
>have any new answers emerged for XML?
>The only one I can think of is that we didn't have 
>the DOM.

The primary answer I give this question is flexibility, though there is a
significant cost in efficiency.  XML documents can easily hold structures
that make relational databases choke, though finding data in an XML
document describing a table will be a lot slower than finding that data
when it's stored in a relational database.  If you're storing data that
doesn't live happily in columns, rows, and tables, and especially if you
need access to it across platforms and languages, XML is a lot more
capable, though not as quick.

XLink also has promise in this regard, offering far more flexible and
descriptive connections between data sources (aka documents) than the
relatively (and quite efficiently) austere connections between tables in an
RDBMS.  How this works out in the long run will depend on how that spec and
XPointer come out, but there is promise as well.  (The discussions
surrounding XML query languages may have more direct impact, though.)

XML isn't going to replace RDBMS systems, though it may relieve them of
some burdens for which they weren't particularly well suited in the first
place.  As David Megginson puts it:

>Different species, but they can be taught to play together nicely.

Sounds good to me!

Simon St.Laurent
XML: A Primer / Cookies
Sharing Bandwidth 
Building XML Applications (February)

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