Rules overview

Rules are created and stored in the catalog database, and you can modify them using Paragon. A rule (DRULE element) is constructed from a tree of logical expressions (in RLOGIC elements). Rules use the following hierarchy in the Dabacon database:

• RLSWL - Rule Set World element

• RLSET - Rule Set element

• DRULE - Design Rule element

• RLOGIC - Rule Logic element

• RVALUE - Rule Value element

Each RLOGIC and RVALUE element contains a single Programmable Macro Language (PML) expression that a database element (the evaluating element) can evaluate. The expressions on RLOGIC elements must evaluate to boolean TRUE or FALSE, while the expressions on RVALUE elements are evaluated to provide the output value of the rule.

The Rules Engine iterates through each RLOGIC element and evaluates its expression with respect to the evaluating element. If it evaluates as TRUE, the Rules Engine repeats the process on child RLOGIC elements. The Rules Engine repeats this process until it finds an RVALUE element that contains an expression to be evaluated to give the rule value.

In the example rule, the Rules Engine evaluates the properties RPRO PTHK and RPRO PLTW for the evaluating element. Depending on the values evaluated, the Rules Engine returns a value of 10 mm or 15 mm.

An RLSET must contain rules that are valid for a single type of element. This convention helps to ensure that the rule evaluates the expressions within the rule successfully. The PURPOSE attribute of the RLSET controls which context the rule set is valid. DRULE elements within the rule set define rules intended to be run for this element type. DRULEs are usually defined to set attributes for the element, but they can provide another function, depending on the PURPOSE attribute of the DRULE.