An associative engine in CAD/solid modelling software is the component which maintains the associative relationships between the collection of geometric entities. The associative relationships are basically LISP

Lisp

A lisp is a speech impediment, historically also known as sigmatism. Stereotypically, people with a lisp are unable to pronounce sibilants , and replace them with interdentals , though there are actually several kinds of lisp...

 expressions which describe the orientation and placement of two or more geometric entities in relationship to each other. The AE will force a regeneration through the use of transmigration operations if a user changes any of the associations used to make up the final change state.