Hindu seers, gurus and scholars recognize the three functions of Creation, Preservation and Dissolution all stem from one Supreme force 'Brahman'. They are defined as different aspects of the same force and attributed to Brahma, Vishnu and Shiva in that respective order for the convenience of the seeker as the ultimate Supreme reality is formless.
This in essence the contemplative portion of the Veda ( all four) where there is no differentiation is made. Usually it is the last or end chapter and hence known as Ved-Anta. In the Samhita (Mantra hymns) and Ritualistic portions the differences between the roles of Brahma,Vishnu, Rudra, Indra, Skanda and others are elaborated.
Subsequent interpretations, in Smritis, of who is the Supreme being itself, two prominent schools of thoughts emerged one under Vishnu and other Shiva. Both believe that their aspect of God define fully and completely the Supreme power. Saiva Sidhantham is one of the derivatives we discussed in this forum in the past weeks.