For example, the verb kataba "to write is obtained by attributing the verbal scheme fa'ala to the root ktb, the noun maktab "desk is formed attributing the scheme maf'al in which the prefix ma indicates the event location.
each unit is defined by two criteria: a) a morpho-semantic criterion, namely, the root and ii) a morpho-syntactic criterion namely the scheme (Kouloughli, 1994).