A fairly decent solution would be to have parameter arrays that could be
indexed, but that's on PTC to come up with.
A modern solution would be to have no historical information on the
drawing itself and depend on the PDM system to handle that. I've seen
some small drawings where the change block has enough information to
un-draw the changes (Zone B2 2.550 dimension was 2.540, for example)
All the important information about the management and control of the
drawing should be in the PDM system and only enough information on the
drawing to see if it's a match to what's in the PDM system. The PDM
system itself should annotate anything that is copied out with revision
and sign-off status information, and also who copied it out and when.
Taken to the extreme - Why are there signature blocks on CAD drawings
when there is no realistic way to sign a CAD file? Even if it is opened
by each signer, they are modifying the drawing from what the previous
signer saw, in a way that is not limited to adding the signature. With
the PDM system, the signed-off drawing should be the same for all of the
signers.
Back to the revision tables - sometimes there is interest in having
individual sheet revisions. Typically all sheets of a drawing are in a
single file, and you can't change any one sheet without changing the
whole file, so why complicate life? I suppose one could make a separate
file for each sheet, but that would make sheet numbering an additional
headache. It's one thing to deal with a drawing where a sheet may or may
not have been altered, but nothing like the joy of trying to tell
someone which of the three sheet 5s need to have their sheet number changed.
To speed access to history information, I had a semi PDM system (Wiki
based) with individual drawing pages that included copies of all
revisions and all changes and included detailed descriptions of what
changed and why it changed. It linked to any related analyses or other
support material. Often I used Photoshop to overlay the old version with
the change or the new version**. This check file was also attached. It
wasn't a workflow management system that controlled the release status
of drawings, but it nicely covered the info most people want when they
are curious about how a drawing/design got that way.
Dave S.
** Why Photoshop? Because it can (manually) handle views and notes and
balloons that are moved either on the same sheet or to another sheet,
and re-flow or re-pagination of text, and could compare scanned versions
of drawings with re-drawn plotted versions. The overlay file could keep
the entire check markup for all the versions/revisions of a drawing. In
Photoshop Elements it was entirely manual, but in Photoshop, a lot of
the overlay work was automated. I tried GIMP, but at the time it was
sluggish for certain selection processes. It might be faster or newer
hardware might be good enough.