[cad-linux] File formats - linked files for object re-use

  • From: Bruno Postle <bruno@xxxxxxxxxx>
  • To: CAD Linux list <cad-linux@xxxxxxxxxxxxx>
  • Date: Thu, 11 Sep 2003 00:23:04 +0100

[Continued: Discussing a data format that uses filesystem structures
instead of monolithic files]

On Mon 08-Sep-2003 at 05:24:05AM +0200, Janek Kozicki wrote:
> ... (one block can be softlinked to many places, attributes could
> also be softlinked (eg - between drawings ...

Using filesystem links as references is efficient in terms of
storage space, but it has certain drawbacks:

*  Links don't survive diff, patch, cvs, zip, http or smb transfer
   (though they are OK with tar, ftp and nfs).

*  Working with thousands of individual files means using tricks
   such as FAM or dnotify to monitor the data - These tools can tell
   if a link has changed but they can't tell if the destination that
   the link points-to has changed.

*  'soft' links can point to anything (including non-existing
   locations), but they can't convey important information such as
   transformations, measurement-units or conditions - such as "link
   to these directories, but ignore the following parts" or "link to
   this object but scale by 10%" - The sort of complex relationships
   that are needed for polymorphic inheritance.

So, I think that a reference/pointer in a distributed CAD format
really needs to be more than just a soft or hard link?


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