Model 1 ?Person Writes
Model 2 ?Person Writes UNIQUE No
Yes
Model 3 ?Person Writes UNIQUE Annually
Monthly
Weekly
Daily
Hourly
Model 4 ?Person Writes Fun_letters
Long_letters
Perfumed_letters
On_colored_paper
When_they_want_somthing
About_their_cats
The first model represents letter writing as a "unary" concept.
If "Writes" is present it means the person writes letters.
Absence is ambiguous and could mean the person doesn't write
or there is no data.The second model is "binary"; it represents an either/or situation. "Writes" will be present for both "No" and "Yes" objects. A query on "Writes" might be used to identify people for whom letter writing status is truly known.
The third model supports a "fuzzy" notion of letter writing. "Writes_me_letters" is used here to imply that a person writes to some extent, the frequency varying across some spectrum.
The final model is even fuzzier since "Writes" might imply that any or all of the categories that follow it apply.
It is possible to construct very complex trees using nothing but "cascades" of labels to represent more than one concept.
?Person Writes UNIQUE No
Yes Frequency UNIQUE Annually
Monthly
Weekly
Daily
Hourly
Qualities Fun_letters
Long_letters
Perfumed_letters
On_colored_paper
When_they_want_somthing
About_their_cats
Entering this data:
Person Sarah Annually Long_letters About_their_catsResults in this display:

[Thanks to Otto Ritter for introducing the "unary", "binary" and "fuzzy" concepts to me]
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