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Exercise 18: Completed rule implementation
Implement SolveRule and Derive:
SolveRule
SolveRule Input:
 | A rule. |
| The derivation target: An ITransOutput that represents what is trying to be derived. |
SolveRule Output:
A list of entities. For relationship rules, this will be either null to represent failure or the true entity to represent success. For assignment rules, this will be a list of entities that satisfy the value of the assignment.
SolveRule Algorithm:
| Run SolveConditions. |
| If the resultant list is empty, return an empty list. |
| If the resultant list isn't empty and the conclusion type is a relation, then return the true entity. |
| If the resultant list isn't empty and the conclusion type is a property value, then process each result iteratively. Use the conclusion's value specifier to create the result. This can be accomplished by implementing an Eval function for IValueToken which takes a dictionary of variable values, substitutes them, and returns the resultant entity. |
For each result:
| Add the resultant token to the output list. |
Derive
Derive is called with a PropertyToken or RelationshipToken.
Algorithm:
| Look up rules that might be able to derive the value/relationship. |
| For each potential rule, determine whether it is really a match. In the process, determine the value of any variables in the conclusion by doing a token-by-token comparison of the conclusion with the derivation target. Implement this functionality as RuleSolver.Match. |
| Attempt to solve any rules that match. |
| If any rules can be solved, return the resulting value, which will be an IEntity for derived property values or a bool for derived relationships. |
Test Cases
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Web UI
| Add a new text area to the web UI that allows rules to be specified. |
| If the answer to a user's question is a property whose value is not known, try to derive it. If it can be derived, return the result. Always indicate whether a value was derived. |
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