[sugar] Dependency Handling in the Journal

[Marco Pesenti Gritti]

On Fri, 2007-04-13 at 17:31 -0500, Ian Bicking wrote:
> Benjamin M. Schwartz wrote:
> > I posted this on the wiki, but I thought I'd mention it here.  I think the
> > journal should track inter-file dependencies.
> > 
> > Many files we create depend on other files.  The most common example is probably
> > documents that contain pictures.  In some document formats, these pictures are
> > copied into the document, and in others they are referenced by location.  To
> > avoid wasting storage space, we would like to insert pictures by reference
> > (like in .html or .dvi) rather than include them (like in a .pdf).
> 
> Another option here is copy-on-write, where effectively if you use a 
> resource you make a copy of it.  So if you insert a picture into an HTML 
> file, then the picture is "copied" into it.  It doesn't have to be 
> physically copied (to save space) but can just be copied when it needs 
> to be (e.g., if the original image is edited or deleted).
> 
> This seems simple to explain to users (because you don't have to explain 
> it to users at all, things Just Work).  It requires a richer sense of a 
> resource than just a file -- a web page, for instance, is not just an 
> HTML file, but a whole set of files that include all the embedded resources.
> 

I think this is the behavior we want in most cases if not in all. Once
an object is inserted into a different document, it's conceptually a
copy, applying the changes to the original would be confusing.

Marco