1. A system for determining EDI rules to enforce, comprising: a computer system having a processor, a memory, a storage device, a network interface, and a bus for exchanging information therebetween, the memory storing computer usable program code executed by the processor to: determine entity-specific rules from corresponding companion guides for each of a plurality of entities; express each entity-specific rule in a neutral and machine readable format; classify each of the entity-specific rules by determining for each entity-specific rule: whether the entity-specific rule is common with at least one other entity-specific rule, or whether the entity-specific rule is similar to at least one other entity-specific rule, or whether the entity-specific rule is unique; convey results of classifying the entity-specific rules by: creating an inventory of rules, the inventory including a common set of rules for the plurality of entities; dynamically adjusting said inventory of the rules based upon the entity-specific rules where the entity specific rules are derived from a plurality of companion guides, each companion guide associated with one of the plurality of entities; storing the inventory of rules in a storage according to the classification of each rule as common, similar, or unique; creating a respective, corresponding pointer to the entity-specific rules in the inventory of rules associated with at least one of the plurality of entities; and storing the corresponding pointer in a storage for use in retrieving an appropriate current rule set when validating an EDI document for the at least one of the plurality of entities.