# Rule Declaration Language

The rule declaration language supports two types of rules: Decision rule or a Score rule.

#### Score rule:

* A Score rule is composed of one or many rule sets.
* Each rule-set computes a sub-score and is applied a weight.
* The total score then would be the sum of all the individual scores of all the rule sets belonging to a rule.
* A rule set is composed of one or many rule rows.
* You can ‘roughly’ think of each Rule Row as a Conditional evaluation of the facts (a.k.a antecedent) & a score based on these conditions (a.k.a consequent).

<figure><img src="https://user-images.githubusercontent.com/15995686/193492161-71f5faf5-e206-4543-a005-7681b79fe689.png" alt=""><figcaption></figcaption></figure>

#### Decision rule:

* A Decision rule is always composed of only one rule set.
* A rule set is composed of one or many rule rows.
* You can ‘roughly’ think of each Rule Row as a Conditional evaluation of the facts (a.k.a antecedent) & a decision based on these conditions (a.k.a consequent).
* A decision rule always arrives at a single decision at the end of parsing.
* The decision can be anything (a numeric, a string such as YES/NO or even a JSON)
* Once a Rule Row evaluates to True, the corresponding decision is returned immediately.

<figure><img src="https://user-images.githubusercontent.com/15995686/193492209-52bfa8fa-eb27-4805-bf95-cc7723b26a51.png" alt=""><figcaption></figcaption></figure>

#### Antecedent and Consequent

* An antecedent at the core is an evaluator. It evaluates one or many facts through an operator.
* For evaluating numeric facts, a numeric operator is used. It can be one of (<=, <, >, >=, ==, <>, between, is\_none)
* For evaluating string facts, a string operator is used. It can be one of (in\_list, contains, is\_none, equals)
* You can mix evaluation of more than one fact & combine the result with an “and” or “or” condition.
* You can perform complex evaluations involving multiple facts combining AND and OR conditions recursively in the antecedent. See [Examples](/simple-rule-engine/examples.md).
* A rule can be part of another rule. See [Examples](/simple-rule-engine/examples.md).


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