Using python for a CAD program

David Cuthbert dacut at kanga.org
Sat May 20 09:19:24 CEST 2006


Terry Hancock wrote:
> I disagree that transactions are bad for CAD -- they may have
> a different semantic role and the needed granularity may be
> different, but the need to roll data back to an earlier revision
> is just as present in drawings as it is for code or financial
> transactions.

Sure, but that's called source control.  So you do need transactions, 
but for the entire database state, not on database operations.  (This 
was certainly true at Cadence -- there was a thriving third-party market 
for handling source control on CDBA databases, and I never encountered 
any code which operated on the database in a transactional manner. 
OpenAccess did have some basic support for transactions, but I never 
heard of anyone using them.)

Some kind of transactionality is needed for undo/redo, but this is 
usually done in a different (some might say "more efficient", others 
might say "hackier") method than how transactions are implemented for 
RDBMS (that I've dealt with, anyway).  I suspect this can be attributed 
to two major factors: concurrent access is never an issue in such 
systems, and the number of database objects representing a given state 
is far larger than in, say, e-commerce.




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