fogus.rv.productions — me.fogus/rv 0.0.13

The simplest possible production rules system. A run pairs two abstractions: a knowledge base (facts + rules) with an engine (a rule-selection strategy paired with a quiessence-detection strategy).

A production rules system is built from two abstractions:

1. A knowledge base is the rules and the facts they operate on (the WHAT)
2. An engine is the policy that applies the rule processing (the HOW)

Productions are represented as maps having two privileged keys: {:antecedent ... :consequent ...}

The :antecedent key in the production map contains a sequence of EAV 3-tuples with logical variables at key locations for the purpose of pattern matching:

[[?id :person/name "Fogus"] [?id :language/speaks ?lang]]

The antecedent describes the patterns that must be present in the EAV set in order for the production to activate. The antecedent is also known as the left-hand-side (LHS) of the production.

When a production activates, the structure in the :consequent key in the production map is applied to the knowledge base to potentially create new facts. The consequent also contains a sequence of EAV 3-tuples with logical variables at key locations. However, these tuples describe new facts with values bound to embedded logic variables as defined within the antecedent context of a production activation.

A production set is a data structure defined as such:

1. A production set is simply a vector of production definitions
2. A production definition is a map containing :antecedent and :consequent keys
3. An antecedent is a vector of EAV 3-tuples representing patterns in data
4. An EAV 3-tuple is a vector of three elements: id, attribute, value
5. A consequent is a vector of EAV 3-tuples representing new attribute assertions

A fact base is a set of EAV 3-tuples.

A knowledge base is a map of productions and facts, mapped to keys:

{:productions #{...} :facts #{...}}

An engine describes how a knowledge base is processed: which matching production fires next, how the stream of successive fact sets is shaped, and how quiessence is detected:

:rule-choice -> fn to pick which production fires next :state-xform -> transformer of fact-set states :quiesce -> a completing reducing function that detects when to stop

The production rules system implemented herein runs an engine against a knowledge base in four stages:

1. Antecedent unifications over the KB's facts
2. Production selection via the engine's :rule-choice
3. Consequent substitution and assertion
4. System quiessence via the engine's :quiesce, through :state-xform

apply-production clj

(apply-production production facts context)

make-engine clj

(make-engine & {:as config})

Constructs a production rules engine from input functions:

:rule-choice -> fn to pick which production fires next :state-xform -> transformer of fact-set states :quiesce -> a completing reducing function that detects when to stop () initial accumulator (state) extract the final fact set (state s) new state, or (reduced acc)

run clj

(run {:keys [rule-choice state-xform quiesce]} kb)

Runs a production rules engine against a knowledge base, driving the state stream through the engine's transducer and quiessence function until quiessence is reached, then returning the final fact set.

select-production clj

(select-production selection-strategy {:keys [productions facts]})

Builds a sequence of bindings paired with each production and then uses a selection function to execute one of the productions that matched.

states clj

(states choice-fn kb)

Will apply the result of one production firing to the fact base and feed the result forward into the next firing. The production selection is driven by choice-fn.

step clj

(step kb)

(step choice-fn kb)

Takes a set of productions and facts and returns a new fact base based on the application of single production.

unifications clj

(unifications [clause & more :as clauses] facts context)

Walks through all of the clauses in an implied antecedent and matches each against every fact provided. Returns a seq of contexts representing all of the bindings established by the antecedent unifications across all facts provided.