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- To: "Roger L. Costello" <email@example.com>, <firstname.lastname@example.org>
- Subject: RE: [xml-dev] Designing XML to Support Information Evolution
- From: "Hunsberger, Peter" <Peter.Hunsberger@STJUDE.ORG>
- Date: Mon, 17 May 2004 13:01:12 -0500
- Thread-index: AcQ8L2V7U8ZIgcWWTwWd5kHRhhqiogAB/xYg
- Thread-topic: [xml-dev] Designing XML to Support Information Evolution
Roger L. Costello <email@example.com> writes:
> Here are some lessons I learned. I believe these lessons apply to all
XML information structures where you have a requirement to
> evolve the information structure by moving the information (e.g., move
the Picker around to different lots), changing the
> information values (e.g., a Pickers harvests ripe grapes, thereby
decreasing the value of <ripe-grapes> on a lot), and where
> parallel processing of the information is desired/needed. I don't
know if these lessons apply everywhere.
> 1. How you structure your information in XML has a tremendous impact
on the processing of the information.
> 2. Hierarchy makes processing information hard! There exists a
relationship between hierarchy of information and the
> complexity of code to process the information. The relationship is
roughly: the greater the hierarchy, the greater the
> complexity of code to process the information (Some hierarchy is
good, of course. But the amount of hierarchy that is
> good is probably much less than one might imagine, certainly less than
I thought, as described above.)
Hierarchy makes processing non-hierarchical data hard. As others have
suggested, it would seem that you created a hierarchy where none was
needed. You can always normalize a hierarchy in a database (eg.
set/subset relational models for example), but when trying to reflect a
hierarchy for presentation purposes a hierarchy is the best way to
represent hierarchical data... Gluing back together parent child
relationships can also be inefficient!
> 3. Flat data is good data! Flatten out the hierarchy of your data.
It makes the information flexible and easier to process.
For raw data: definitely. You touched on this indirectly, but I think
it's worth noting that for things like SAX pipelines, deep data
structures allow less concurrency; in a pipeline, you can only start on
a element when you know the previous step has finished with it, deep
hierarchies obviously slow that event down. When we need a hierarchy we
have a metadata model that maps the hierarchy, the data that gets mapped
to this structure is flat.
> 4. Order hurts! Requiring a strict order of the information makes for
a brittle design. It is only when I allowed the lots
> and pickers to occur in any order that the flexibility and simplicity
> Comments? /Roger