is2150_hw3_stm57

is2150_hw3_stm57 - Steven Madara IS2150 Prof. Joshi Due:...

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Steven Madara IS2150 – Prof. Joshi Due: 10/6/09 HW #3 1. Section 2.6 (1a) Alicerc Bobrc cyndyrc Alice o,x r Bob r o,x Cyndy r r,w r,w,o,x (1b) Alicerc Bobrc cyndyrc Alice o,x r r Bob o,x Cyndy r r,w r,w,o,x (2a) command delete_all_rights(p,q,s) delete read from a[q,s]; delete write from a[q,s]; delete execute from a[q,s]; delete append from a[q,s]; delete list from a[q,s]; delete modify from a[q,s]; delete own from a[q,s]; end (2b) command delete_all_rights(p,q,s) if modify in a[p,s] then delete read from a[q,s]; delete write from a[q,s]; delete execute from a[q,s]; delete append from a[q,s]; delete list from a[q,s]; delete modify from a[q,s]; delete own from a[q,s]; end (2c) command delete_all_rights(p,q,s) create object d; enter write into a[q,d]; if own in a[q,d]
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then delete write from a[q,d]; if modify in a[p,s] and write in a[q,d] then delete read from a[q,s]; delete write from a[q,s]; delete execute from a[q,s]; delete append from a[q,s]; delete list from a[q,s]; delete modify from a[q,s]; delete own from a[q,s]; destroy object d; end Section 3.5 (1a) In the ACM model we are only testing for the presence (not absence) of rights in the entries. These tests are made up of primitive tests – each of these tests checking for the presence of a right in the ACM entry. For A[s 1 ,o 1 ] and A[s 2 ,o 2 ] – different tests are run to check for the presence of a given right in each. If you then look at the same tests for A[s 1 ,o 1 ] and A[s 1 ,o 2 ] = A[s 1 ,o 2 ] U A[s 2 ,o 2 ], all of the tests that were performed on A[s 2 ,o 2 ] will now be performed on A[s 1 ,o 2 ]. A[s 1 ,o 1 ] has not changed so the results of the test will not be different. A[s 1 ,o 2 ] will also have the same test results since it is still checking for the presence of a right (A[s 1 ,o 2 ] is a superset of A[s 2 ,o 2 ]). The output of these primitive tests has not changed, so the overall output will not change. (1b) No, the above would not hold true if one could test for the absence of rights as well as for the presence of rights. 2) (1) Partial Order 33 23 32 13 22 31 12 21 11 (2) A lattice is the combination of a set of elements S and a relation R meeting the following criteria: R is reflexive, antisymmetric, and transitive on the elements of S. (Let ‘*’ represent the “less than or equal to” relation, for below) R is reflexive (a*a for all s that exist in S)
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This note was uploaded on 02/07/2012 for the course SIS 2150 taught by Professor Joshi during the Fall '11 term at Pittsburgh.

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is2150_hw3_stm57 - Steven Madara IS2150 Prof. Joshi Due:...

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