CSC 750
Service-Oriented Computing
H3
1/10/2007 Solution and Grading Key
1. (8 points) Which of the following statements are true about the distributed truth maintenance system that we
discussed in class?
A. Well-foundedness means that beliefs may not depend upon rules
B. Well-foundedness means that rules must be believed as premises, and cannot be given a justification
C. Well-foundedness means that beliefs of one or more agents cannot be circular
D. Well-foundedness means that if agent Charles has a belief (externally) justified based on agent Diane,
then Diane may not hold a belief (externally) justified based on Charles
Solution: C
2. (8 points) Identify all of the following statements that are true about rules
A. Rules are executable but not inspectable
B. Rules can be written up quickly and achieve a lot more than traditional languages; this is why there is
never a need to create them incrementally
C. We can use description logics and rules together to represent knowledge
D. Rules ensure that if a transaction has been initiated, then it will complete
Solution: C
3. (8 points) We are given four agents: Arvind, Brian, Carolyne, and Julius. As discussed in class, the agents
communicate via asynchronous messaging: the send and receive of a message are separate events. We know that
•Arvind sent a message to Brian on Monday.
•Carolyne sent a message to Julius the following Tuesday.
To fix the terminology, consider two vectors, v1and v2, of equal dimensions.
•We say that v1is smaller than or equal to v2(or v1v2) if and only if each element of v1is smaller than or
equal to the corresponding element of v2.
•We say that v1is smaller than v2(or v1≺v2) if and only if (v1v2and v16=v2).
•We say that v2is greater than v1if and only if v1is smaller than v2.
Identify all of the following statements that are true with reference to vector clocks:
A. The timestamp of Carolyne’s message must be greater than the timestamp of Arvind’s message
B. The timestamp of Carolyne’s message may be smaller than the timestamp of Arvind’s message
C. The timestamp of Carolyne’s message would be greater than the timestamp of Arvind’s message if
Brian sent a message to Carolyne before she sent her message to Julius
D. The timestamp of Carolyne’s message would be greater than the timestamp of Arvind’s message if
Brian sent a message to Carolyne after he received Arvind’s message, and before Carolyne sent her
message to Julius
Solution: B is false because Carolyne’s message has a later timestamp for her local clock than any message
sent by another agent.
Notice that D is false because Carolyne need not have received Brian’s message prior to sending her message
to Julius
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