Basic existential ruleform. Ruleforms are tabular data structures that define the structure of rules. All columns of a ruleform can be divided into factors and considerations, which roughly correspond to the antecedent and consequent, respectively, of an "if/then"-style construction. Factors are the means by which rules are addressed and selected, and in practice are implemented as keys in a database system. The remainder of the columns are known as "considerations", and provide metadata about a rule, as well as additional information that may influence the ultimate processing of a rule. The ruleform shown here is a simplified version of the BioEntity ruleform, which is used to define the existence of concepts and entities that participate in various biological processes. It is also an example of an existential ruleform, which is used to declare the existence of entities in the system.