chaining @headers and cycles [was: Re: function and impacts...]

On 25 Sep 2008, at 4:24 AM, Henri Sivonen wrote:
>> [...]
>
> Here's an example of a table with at least one headers/id cycle:
> http://www.usdoj.gov/jmd/fass/afvreport2005.htm
>
> Regardless of how common this is, if headers cells can be chained  
> AND authors can add arbitrary header associations, it is *possible*  
> to construct a cyclic header chain. A proper spec must, then,  
> define in detail what an agent is to do with cycles.

Here's one processing rule that I would submit for consideration:

Grow a running set of the nodes that are included in self 
+recursivelyRelatedBy@headers.  When an @headers arc (one ID
appearing in an @headers attribute) leads to a node
already in that set, drop _that arc_ (quietly) and continue to
follow the rest.

This allows for mutual dependency without creating
a non-terminating process.

> (What does existing client software do, btw?)

I'll try to get this confirmed, but AFAIK the present implementation
does not chain @headers references.  I just reads, when asked, the
contents of the cells mentioned in the @headers of the cell where
the focus was when the AT was asked for more info.  Maybe in  
conjunction with the first-in-row, first-in-column heuristic headers.

Al

> -- 
> Henri Sivonen
> hsivonen@iki.fi
> http://hsivonen.iki.fi/
>
>
>