It would be useful to be able to define properties in a way that I don't need to
define them in every job.

Example:
Instead of doing this: "ant target
-Ddatabase-src.dir=<hudson_dir>/jobs/database/workspace/database/src"
in every build, I could define the property in system configuration.

I would need to define the path in just one place,
and pass it to ANT like this: -Ddatabase-src.dir=${DATABASE_SRC_DIR}.