Figure 2-7 shows the same model organized according to the starry skies positional conventions that will be adopted in this book. That is, the asterisks (the “many” side of the relationships) are always to the left or toward the top of the diagram.

This has the effect of putting entity classes representing tangible objects (such as Party) in the lower right area of the diagram, and putting those represent­ing the less tangible roles, interactions, and transactions (such as Observation) in the upper left.

Note that even without prior knowledge of the laboratory, you can see that the focus of the dia­gram is Laboratory Test conducted on Sample, and the results describing each Sample (Observations). Some entity class

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