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Policy Definition Problems
Policy Definition faces a number of problems. Perhaps the most critical is the scalability of rules.
How many rules does it take to restrict or allow a certain behavior? Will the rule sets still be manageable after a while?
Will a default deny or a default allow policy be appropriate? And will default deny work on a global level? This can cause complete system lockup if improperly used but is much safer because no program can escape (e.g. a newly installed program)
Do rules work only on instance level (e.g. on file /tmp/foo/bar.xml) or only on class level (e.g. all objects of type "file") or both. And how are sets of resources defined? Usually some kind of wildcard (globbing) system is needed like /tmp/*)
What kind of logical operations are possible within rules: counters, and, or etc. Can identity information be used as well (e.g. rule x applies if user is y)
And last but not least the way the rules are expressed. Most policies follow a subject, action, object pattern here which matches the way many natural languages express access rights and restrictions.