FAQ: successive releases in the same or separate directories?

Should successive releases of a 3rd party product maintained in a vob, be installed on top of each other or as separate elements?

There are pros and cons, but roughly, I answer: on top.

Version exclusion

If saved as versions of the same elements, files belonging to different releases will be supported as true configuration items with ClearCase support. ClearCase will ensure that not two different versions are used in the same configuration.
If the files are different elements, there is no such guarantee.

Shared items

Different releases may share items, especially text files (headers, configuration files, sources...). It may be worthwhile tracking the actual changes!

Convenience of use

If the paths change, the rules in our own makefiles, or our soft links, or something will have to be changed. This will propagate the dependencies, and make switching back and forth between versions more difficult.

Ease of update

Of course it is easier to dump releases in different directories: trying to maintain version trees may require significant renaming and moving, and has to be done by hand.
The benefits are not always obvious, and thus the tradeoffs hard to evaluate.