Short-Term Facts vs. Long-Term Facts

Two types of facts are asserted into the working memory of the rule engine—short-term facts and long-term facts.

Short-Term Facts

A short-term fact is specific to a single execution cycle of the rule engine. Short-term facts are retracted automatically from the working memory of the rule engine after the policy executes. If your data changes between execution cycles of the rule engine for a policy, you submit the data as a short-term fact to the rule engine.

Examples of short-term facts are:

• The facts you submit as parameters to the Policy.Execute method.

• The facts you submit as parameters to the Call Rules shape.

• The facts you submit from an action of a rule using the Assert function.

Long-Term Facts

A long-term fact is loaded into the working memory of the rule engine for use over an arbitrary number of execution cycles. Typically, long-term facts are slowly changing facts that do not typically change between executions of a policy. For example, you may want to create a database connection only once, and execute the policy several times by using the same database connection. The only real distinction between short-term facts and long-term facts is in implementation.

To submit a fact as a long-term fact, you need to perform the following steps:

1. Create a fact retriever component that implements the IFactRetriever interface. Create and assert the fact into the working memory of the rule engine when the UpdateFacts method is invoked for the first time, and update the fact when necessary on subsequent invocations of the UpdateFacts method.

2. Configure the policy to use the fact retriever component by using the Business Rule Composer.

   For more information about creating a fact retriever and using it in a policy, see How to Create a Fact Retriever.

See Also

Facts