RQTS : tag order

Gregor Hagedorn G.Hagedorn at BBA.DE
Mon Dec 13 16:21:15 CET 1999

Bob Morris wrote:

> Here's a proposed requirement for data exchange, brought home by one
> of Leigh's examples:
> <RQT> It should be possible from the data itself, perhaps together
> with external resources to which it refers, for software to determine
> whether the order matters for any collection of tags in the
> data.</RQT>

I agree, especially that the software should be able to determine it.
Regarding XML, tags, and DTDs, I believe, the assumption is that
order does not matter, wherease an order can be imposed on attributes
within a tag, correct?

> One answer is "order always matters". That would be regrettable. For
> example, being able to detect that some list is unordered can make it
> easier to know whether two data streams represent the same
> object. (That's probably a deeper desideratum.)

Does order matters for our problem? Where would it matter, any
examples from descriptive data?

In fact, thinking in my own relational information model, we have a
problem here: Some parts of the structure will be relating to
records, i.e. instances of an entity type. In my thinking, the order
of items to be described, and the order of characters used to perform
the description should NOT matter. It is a plausible user requirement
to report any of them in any order.

That does not mean that characters or states do not have an order,
but this order is secondary, and multiple orders are desirable. Being
ordered should not be a requirement of the exchange format.

However, there are other data elements that refer to attributes of
entities. Ordering them makes some parsing operations easier.
However, what fundamental advantages would it have to impose an order
on them?

Finally, some item are ordered, e.g. it will be desirable to impose
an order on multiple states in a descriptions. Written in (loose)

1,1/<rarely>2 -> Flowers blue or rarely white

may be different from

1,2/1<rarely> -> Flowers white or rarely blue

However, I believe that the DELTA method of using a text-sequence is
not necessarily the best solution. Alternatively, a data element may
be introduced to store the ordering information. For example,
DeltaAccess handles this problem with the numeric SEQ attribute of
the DESCR entity.

Gregor Hagedorn                 G.Hagedorn at bba.de
Institute for Plant Virology, Microbiology, and Biosafety
Federal Research Center for Agriculture and Forestry (BBA)
Koenigin-Luise-Str. 19          Tel: +49-30-8304-2220
14195 Berlin, Germany           Fax: +49-30-8304-2203

Often wrong but never in doubt!

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