Folks, Quiz1 has been graded.
Here's a response that got 10/10:
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D3 and D4, both are based on the fact that a tree is well-formed if each leaf has only one reference to its parent (this is what we call "back-reference" or BR). In particular, the directories need to fulfil:
- D3: the directory needs to form a tree with a single root with arcs that are defined as the reverse of the back-references. One detail here is that during the process of moving a subtree this condition is a little looser: each arc is mapped to one or more BR, and at least one of them should fulfil this condition.
- D4: Each Directory reference (arc of the tree) is defined by a BR that will expire after it. Basically, this means that we keep the structure well-formed by making sure that there are only arcs created from well-defined back-references.
In short, both constraints tell us how to properly define a tree from a structure that we know how to properly constraint in order to have a well-formed tree.
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The question was: "Which constraints ensure that the directory tree remains well-structured?" In other words: "Which constraints ensure that the directory tree remains a tree?" Some of you interpreted the question as: "Which concepts/techniques ensure that the system operates correctly/well?" Understandably, you felt that the question was too hard (indeed, to answer the latter question, one would need to summarize most of the paper).
We did not want anyone to fail for misinterpreting the question, especially since this was our first quiz. Hence, we awarded 6/10 to those of you who gave a reasonable answer, e.g., summarized correctly the key points made during the lecture. Also, we did not penalize responses that included more constraints than the ones asked for.
For the future: Our intention is that quiz/exam questions be precise and that they can be answered in the allotted time without stress. If you think that a question is vague and/or could not possibly be answered in time, please raise your hand and ask for a clarification.
