  Some theories on data flow security are based on order-theoretical concepts,
most commonly on lattice concepts. This paper presents a correspondence between
security concepts and partial order concepts, by which the former become an
application of the latter. The formalization involves concepts of data flow,
equivalence classes of entities that can access the same data, and labels.
Efficient, well-known algorithms to obtain one of these from one of the others
are presented. Security concepts such as secrecy (also called confidentiality),
integrity and conflict can be expressed in this theory. Further, it is shown
that complex tuple labels used in the literature to express security levels can
be translated into equivalent set labels. A consequence is that any network's
data flow or access control relationships can be defined by assigning simple
set labels to the entities. Finally, it is shown how several partial orders can
be combined when different data flows must coexist.
