Based upon my experiences performing security cooperation duties in the Military Assistance Program (MAP) in Jordan, at a GCC, and at DISAM, I offer some thoughts and comments concerning the SDO/DATT concept.
No. Barley is not wheat at all. Barley and wheat are two different species of cereal grasses belonging to the family Triticeae. Barley does belong in the wheat family, which is, as mentioned, Triticeae, but is of an entirely different species from wheat. The species name for barley is Hordeum vulgare, and the species name for wheat is Triticum aestivum. No doubt either look similar, but both are quite different from the other.
Rye (Secale cereale) is a grass grown extensively as a grain, a cover crop and a forage crop. It is a member of the wheat tribe (Triticeae) and is closely related to barley (genus Hordeum) and wheat (Triticum). Rye grain is used for flour, rye bread, rye beer, crisp bread, some whiskeys, some vodkas, and animal fodder.