eyeprolog

Annotation

Who said what, and when?

A statement often comes with metadata: who stated it and when it was recorded. This example keeps the statement and its annotations together as one piece of data and uses ordinary rules to project the parts it wants to report.

Run it in the playground · Source

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The question

Bob stated, on 7 July 2021, that a is named “Alice”. How do we record the claim and its provenance without asserting everything as global facts?

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The annotation as data

annotation(t, (
  name(a, "Alice"),
  statedBy(t, bob),
  recorded(t, "2021-07-07")
)).

The second argument is a comma term: one data value that bundles three members. Nothing inside it is a fact of the program yet. t names the annotated statement so its metadata can refer to it.

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Walking the bundle

context_member((Left, _right), Member) :- context_member(Left, Member).
context_member((_left, Right), Member) :- context_member(Right, Member).
context_member(Member, Member) :- Member \= (_left, _right).

name(S, O) :-
  annotation(_t, Context),
  context_member(Context, name(S, O)).

log_nameOf(T, name(S, O)) :-
  annotation(T, Context),
  context_member(Context, name(S, O)).

context_member/2 walks the comma term like a tree. Each projection rule then decides explicitly which member becomes a visible relation. log_nameOf/2 keeps the link between the annotation t and the claim it carries.

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The answer

eyeprolog examples/annotation.pl

name(a, "Alice").
log_nameOf(t, name(a, "Alice")).
statedBy(t, bob).
recorded(t, "2021-07-07").

The claim, its link to annotation t, who stated it, and when it was recorded.

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The reason

eyeprolog --proof examples/annotation.pl

step(context_member(name(a, "Alice"), name(a, "Alice")),
     rule(4),
     ['Member' = name(a, "Alice")],
     [name(a, "Alice") \= (_left, _right)]).
step(name(a, "Alice") \= (_left, _right), builtin, [], []).

The proof shows how the claim was found inside the bundle: the walk took the left branch of the comma term, reached name(a, "Alice"), and confirmed with a built-in test that this member is not itself a further conjunction.

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The check

condition('C1', resolution, ok, 13).
condition('C5', re_decision, ok, 3).
recomputed(3).
trusted(0).
claims(4).
verdict(checked).

All 13 rule and fact steps check, and the 3 \= tests are recomputed by the checker.

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Try it

• Add a second annotation u in which Carol states that b is named “Bob”, and predict the new answers.
• Remove the name/2 rule. Is the claim still visible through log_nameOf/2? Why might you prefer that?
• Add confidence(t, 0.9) to the bundle and a projection rule for it.

Learn more in The Art of EyeProlog, Chapter 9.

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