Learn English – Reduced relative clause with “ing”

I have the following construction,

A context variable refers to a subset of the DOM tree nodes which
represent a context.

I doubt if I should say

A context variable refers to a subset of the DOM tree nodes
representing a context.

Or for

….another anchor which shares the same ancestor

…another anchor sharing the same ancestor

Are they both correct? In fact I don't know when to use ing in relative clause.

The examples of this source are in present continues form but examples of this one include present form too.

Can I always use the reduced relative clause with "ing" in present or present continues cases? or it is just for present continues? or for special cases of present? I got confused!