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Relational databases are a horrible way of storing recursive data. Apart
from anything else, recursive queries cannot be done using first order
predicate logic (i.e. SQL, without extensions). If you must do it, Joe Celko
seems to have made a career out of telling people how to do it, but it's no
picnic. Better to choose a container that fits the shape of your data.
Michael Kay
http://www.saxonica.com/
> -----Original Message-----
> From: Robert Koberg [mailto:rob@koberg.com]
> Sent: 24 May 2006 20:53
> To: xml-dev
> Subject: [xml-dev] hierarchical XML in a relational DB
> structure - moving nodes
>
> Hi,
>
> I want to use a relational database to store data that is
> nested and where the order is preserved. I am having a hard
> time wrapping my head around how to do the following mostly
> because I don't have much experience with relational databases.
>
> I am looking at mapping a structure like so:
>
> <node id="1">
> <node id="11">
> <node id="111">
> <node id="1111"/>
> <node id="1112"/>
> <node id="1113"/>
> </node>
> <node id="112"/>
> <node id="113"/>
> <node id="114"/>
> </node>
> <node id="12">
> <node id="121"/>
> <node id="122"/>
> <node id="123"/>
> </node>
> </node>
>
> To a relational database that might have a table representing it like:
>
> Node
> -------
> id
> parentId
> parentIndexPosition
>
> First question: Is using an index position the best way to
> maintain the position? (or is preceding and/or following
> sibling better? or something
> else?)
>
> OK, lets say I have imported some data/XML into the above
> table, giving appropriate parents and index positions.
>
> Next, say I want to move /node/node[2]/node[@id=121] to the
> position /node/node[1]/node[1].
>
> How do you handle updating the index position of other nodes?
> All children of /node/node[@id=12] will need their
> parentIndexPosition moved down one. And all children of
> /node/node[@id=11] will need their parentIndexPosition moved
> up one. (the ID attributes where abritrarily created and
> should not indicate position)
>
> Is there a built in mechanism to do this type of thing in
> relational databases? If not how would an UPDATE look?
>
> Are there any java libraries or articles out there that
> handle this type of thing? (I am having a hard time finding
> anything with google)
>
> thanks,
> -Rob
>
>
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