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Why is the book in parts? It was scanned almost 20 years ago, when multi-megabyte files were still challenging for some tools to deal with. I'm guessing as a single file, it would be 50+ MB.
(Note that the book was written before PDF existed.)
Yup, I'm the author. As I recall, I didn't have much input on the cover. Whoever did the design must have liked the look of the figures. However, as you see, they're pretty hard to interpret with the attribute names removed.
The diagrams are indeed hypergraphs. They are taken from Chapter 12 of the book, and are simplifications of Figures 12.44 and 12.45. The solid lines enclose relation schemes, and the dotted line represent "objects", which here signify groups of relations it makes sense to join. There's a scan of the text at http://web.cecs.pdx.edu/~maier/TheoryBook/TRD.html if you want to look at the figure originals.