Homework 1
Michael Moore
Tim Jinfei Yin
Q 2.1 : Answer questions A-F for Fig 2.15 (pp. 65) for the planar configuration of nodes, directed arcs
and areas. Each answer is a non-negative whole number.
A. What is the maximum number of directed arcs associated with an area?
4 arcs
B. What is the minimum number of directed arcs associated with an area?
2 arcs
C. What is the maximum number of left-bounding area for a given arc?
1 area
D. What is the minimum number of left-bounding area for a given arc?
0 areas
E. What is the maximum number of nodes for a given area?
4 nodes
F. What is the minimum number of nodes for a given area?
2 nodes
Q 2.2 : Answer questions A-F in context of the EER diagram in Fig 2.16 (pp. 65), where answers are
restricted to 0, 1 or many.
Are there any surprises (e.g. ambiguities, violation of your knowledge of geometry)? Explain the
surprises in terms of the purpose of conceptual data model such as EER. Suggest ways to improve EER
diagram to address the surprises. Limit your narrative to 100 words.
From the book: “A directed arc must have exactly one area on its left and one area on its right” and
“...this disallows areas with no bounding arcs...”. Those two phrases contradict. We decided that the
exception to the rule would be that there is an un-bounded plane on which the arcs are drawn, and that
this plane counts as an area, but does not require any arcs.
Although not strictly ambiguous, it was intuitive that an arc could have a single node which was the
beginning and ending node. The EER diagram does not seem to exclude this case.
A. What is the maximum number of directed arcs associated with an area?
many
B. What is the minimum number of directed arcs associated with an area?
0 – Using the note above, and information from page 179 in the book, we decided that the un-bounded
plane counts as an area, the minimal case is 0 arcs, with the plane being the only area.
The book says “...the existence of the specially distinguished area that is the external...”
C. What is the maximum number of left-bounding area for a given arc?
1
D. What is the minimum number of left-bounding area for a given arc?
1
E. What is the maximum number of nodes for a given area?
many
F. What is the minimum number of nodes for a given area?
0 – Using the note above, and information from page 179 in the book, we decided that the un-bounded
plane counts as an area, the minimal case is 0 arcs, with the plane being the only area.
The book says “...the existence of the specially distinguished area that is the external...”