ExtendedEntityClass

ExtendedEntityClass[class,"name"->f] represents an entity class derived from class by adding a new computed property "name" whose value for each entity is obtained by applying the entity function f.

ExtendedEntityClass[class,{name1->f1,name2->f2,…}] adds the properties namei defined by the functions fi.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.