
 TDAN Engle  Data Modeling Left Right 
  The fact is that the meanings of the predicate letters of [basic firstorder] predicate logic vary from problem to problem: Unlike quantifiers, truthfunctional operators, and the identity predicate, they do not have fixed meanings. 
  For these reasons (and others), leftwing data modeling requires the use of “nonstandard” logics, such as semantically dependent logic, higherorder predicate logic, frame logic (Flogic), threevalued logic, and/or probabilitycalculus logic. 
  This approach seems to me to be unrealistic: In order to logically model deeply layered, fully extensible type hierarchies, you must use a higherorder predicate logic. 
 www.tdan.com /i024hy03.htm (2752 words) 
