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Chapter 5. Rule Algorithms
5.1. PHREAK Algorithm
The new PHREAK algorithm is evolved from the RETE algorithm. While RETE is considered eager and data oriented, PHREAK on the other hand follows lazy and goal oriented approach. The RETE algorithm does a lot of work during the insert, update and delete actions in order to find partial matches for all rules. In case of PHREAK, this partial matching of rule is delayed deliberately.
The eagerness of RETE algorithm during rule matching wastes a lot of time in case of large systems as it does result in a rule firing eventually. PHREAK algorithm addresses this issue and therefore is able to handle large data more efficiently.
PHREAK is derived from a number of algorithms including the following LEAPS, RETE/UL and Collection-Oriented Match algorithms.
In addition to the enhancements listed in the Rete00 algorithm, PHREAK algorithm adds the following set of enhancements:
- Three layers of contextual memory: Node, Segment and Rule memories.
- Rule, segment, and node based linking.
- Lazy (delayed) rule evaluation.
- Stack based evaluations with pause and resume.
- Isolated rule evaluation.
- Set oriented propagations.
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