[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Purpose of XML (was: irrelevant title)
First, please don't reply to an existing post when
starting a new thread. Even if you change the title (which you didn't) it makes
following the thread more difficult.
I think we've all been in this position of being told
to use a particular technology for a development, and not being told why.
Sometimes the reasons are good reasons, sometimes they are bad ones. It's
impossible to assess whether it's a good reason in your particular case without
knowing a lot more about the project requirements and environment. It might even
be true that the choice is suboptimal when you take the narrow perspective of
one particular development, but makes sense when viewed from a broader or
longer-term perspective.
I think the primary Purpose of XML (nice
capitalization) in data applications (as distinct from documents) is to achieve
loose coupling of systems. Generally, systems that exchange data using XML are
less tightly coupled than systems that communicate using other technologies.
Loose coupling here means greater flexibility to change either of the systems
without impacting the other, or to add new systems into the mix without
impacting either.
To take an example of extreme tight coupling, I once
came across a system where two companies exchanged data in the form of a binary
image of a SQL Server database. Consequence: neither company could upgrade to a
new SQL server version until the other company did the same (in fact, I think it
couldn't even change the hardware platform). SQL access from one system to
another is not as tightly coupled as that, but it is still constraining: it will
make it difficult to change the data provider to use a different (non-SQL)
technology, and it will be difficult to exploit the extracted data to serve the
needs of a third application. In addition, because SQL data is tabular rather
than hierarchical, it can be very difficult to introduce data structure changes
such as allowing products to have multiple prices in different currencies
without major impact.
Michael Kay
http://www.saxonica.com/
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