Introduction to Datalog

Re:Introduction to Datalog by sdbrady on Monday March 18, 2019 @02:32PM (#19423730)

Thanks for sharing. There is one very significant conceptual error early on, however, and it is captured first in this statement: "The :- means if and only if, or iff". `:-` means if - or more precisely represents material conditional - where the consequent is on the left and the antecedent is on the right. iff is logical biconditional.

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Re:Introduction to Datalog by YeGoblynQueenne on Monday March 18, 2019 @04:59PM (#19425233)

Indeed, ":-" is meant to represent the left-facing arrow of implication. In logic programming papers it is common to typeset it as an actual arrow, for example:

  p(X,Y) ← q(Y,X)

etc.

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Re:Introduction to Datalog by x775 on Monday March 18, 2019 @02:51PM (#19423933)

Hi Stephen. You are absolutely right, thank you for the feedback! I have edited accordingly.

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Re:Introduction to Datalog by maweki on Monday March 18, 2019 @03:56PM (#19424572)

I always remind myself that it's not an if-and-only-if with this argument: since there could always be another rule that is satisfied to make that fact true, it can't be iff.

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