Lesson 10: Using inference

If a query pattern is placed in the condition of a rule, then the statement in the rule’s conclusion can replace the pattern wherever it occurs in the match clause of read queries. This can be used to create simplified abstractions for complex patterns.

The condition of a rule implies the conclusion, but the conclusion does not imply the condition. If a read query matches a statement that corresponds to the conclusion of a rule, it is possible that the statement is satisfied by data on disk rather than by the rule.

Using a rule to dynamically calculate values at query time can prevent stale and inconsistent data resulting from writing the values of calculations to disk.

If the statement in the conclusion of a rule also appears in the condition of another rule, then the rules can be triggered in sequence to form a chain of logic.

If the statement in the conclusion of a rule also appears in its own condition, then the rule can recursively trigger itself.

If two rules have the same conclusion and mutually exclusive conditions, then they represent two alternative branches of logic.

If two rules have the same conclusion but are not mutually exclusive, then both rules can be triggered simultaneously. If the conclusions generate identical data, then the data will only be generated once, and only if it doesn’t already exist on disk.