In some cases, normal forms of fractions makes sense, but in general for fraction fieldss of quotient rings, there is no notion of normal form for a fraction. In other words, fractions may be equal without displaying the same numerator and denominator.
Computations over fraction fields, or polynomial rings over fraction fields, especially GrÃ¶bner basis computations, are much slower than over prime fields. Still, an attempt is made to speed up these computations as much as possible, and more is planned in the future.
For an overview, see fraction fields and frac.
The object FractionField is a type, with ancestor classes EngineRing < Ring < Type < MutableHashTable < HashTable < Thing.