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4. Entity-relationship diagram

This diagram shows the relationship between the elements of the schema. The boxes represent entities. The lines between the boxes represent relationships. The numbers at each end of the connecting lines show the minimum and maximum number of entities at each end of the relationship.

For example, each document has a root element note-set. It contains zero or more day-notes elements, each of which represents a set of notes in one day (and in only one state). Each day-notes element pertains to one and only one note-set.