KE Text syntax is just a syntactic/notational variation of CycL. To some extent, it is a holdover from when Cyc was a frame-based system and CycL was a frame-based language. Many people find it easier and faster to write some types of CycL expressions using KE Text syntax than using "canonical" FOPC-in-Lisp CycL syntax, which partly explains why KE Text syntax continues to be supported by knowledge entry tools.
There are some aliases for directives which are retained for backward compatibility with files written for older versions of KE Text:
- Unit = Constant
- Access Level or AL = Direction
- 0 = :forward
- 4 = :backward
- EL = Formula
In the past you could not include references to a constant in a file/text if the constant appears in a kill expression earlier in the file/text. This would cause problems when the resulting kill expressions are processed by the Cyc Agenda, since the following expressions would reference what is now a dead (non-existent) constant.