Hugh, you and Thomas Beale are apparently colleagues at Ocean, and this is
what Thomas said in the past day or two:
well, yes and no. If you try to make the relational model have anything
to do with the clinical information model, you will usually hit a wall.
Instead, relational databases can be used very effectively as a
low-level store of blobs keyed by path. I wrote a web page on this
aproach which we still have not transferred to the new site, but will in
the next week or so - it may shed some light on the matter.
> The argument of Object databases versus Relational databases is an old
> one that I expect most people have already chosen their camp based
> upon their personal career experiences.
>
I used to think that (seriously) until I realised how bad relational
databases are at storing real-world models of anything but how great
they are as a method of storing blobs, paths, indexable values and so
on, in a totally generic way (i.e. where the schema will not change
regardless of changes in the content of the data, or even its domain
level information model). I believe that the textbook theory of using
either E-R models or object models to represent any but the most generic
things in the real world is relatively useless, for anything but a
demonstration database or small, unchanging application (does such
exist?). For anything real, it doesn't work because a) real-world things
are almost always hierarchical compositions (due to our human way of
describing them) and b) real-world things keep changing (modiyfing the
schema of a database is a pain in the neck when you have 200m records
and 50 tables). Using relational in the classical way works for things
like tax and bank databases because the data are not 'real' things, but
tabular accounting constructs.
* * *
Can I assume that what Thomas here advocates, ("relational databases can be
used very effectively as a low-level store of blobs keyed by path") is
what how the ocean persistence layer actually works? Beyond this, Thomas
apparently has little use for the capacities of Sql-type RDBMS systems to
handle clinical information. Does the Ocean system ultimately amount to
blobs keyed by paths (presumably string paths)? If so, what kind of blobs,
XML blobs, or some other structured text system?
Thanks for your efforts to enlighten me. In that you are making progress :).
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