Halliday & Matthiessen (2014: 262n):
Such clauses have often been called ‘nominal clauses’, in contrast to ‘verbal clauses’, where there is a Process present in the structure of the clause. But this reflects only the view ‘from below’ and hides the fact that in languages such as Arabic ‘relational’ clauses that are marked for aspect and/or polarity typically have a structurally present Process.