Re: Hierarchical databases and semistructured data

From: Morten <morten_at_kikobu.com>
Date: Thu, 21 Feb 2002 12:44:24 +0100
Message-ID: <3C74DD98.3010900@kikobu.com>

I had completely missed the point of model variation in the article, embarrasing. Thank you very much for the enlightenment.

Morten

Jan Hidders wrote:
> "Morten" <morten_at_kikobu.com> wrote in message
> news:3C73F433.2090001_at_kikobu.com...
>

>>Incidentally, I have the book and Buneman's semistructured data article.
>>Their models for semistructured data bring up another question.
>>Do you happen to know if this model has changed - or if there are just
>>several ways of expressing the same model.
>>

>
> The latter. Peter Buneman actually discusses several possiblities in his
> tutorial which are more or less equivalent. The version where only edges are
> labeled is mathematically more elegant, but the one with the labeled leaves
> is more common.
>
>

>>The mismatch is illustrated
>>by the figure in the article, and the figure on page 33 in the book,
>>basically the leaves of the tree in the book have value, whereas they
>>are "void" in the article, but have a label of a "type" (rather than a
>>symbol I assume)
>>

>
> Peter Buneman actually gives three models. The first model has unlabeled
> nodes and labeled edges where the labels can be symbols or a value. The
> second model has edges labeled with symbols, internal nodes unlabeled and
> the leaf nodes are labeled with a value. The third model also labels the
> internal nodes with symbols. I believe, by the way, that he makes a small
> mistake when he presents the third model. The formulation should have been:
>
> type base = int | string | ... | symbol
> type tree = base | label x set(label x tree)
>
> otherwise the type base is never used in the tree.
>
> -- Jan Hidders
>
>
>
Received on Thu Feb 21 2002 - 05:44:24 CST