  We study operational security in computer network security, including
infrastructure, internal processes, resources, information, and physical
environment. Current works on developing a security framework focus on a
security ontology that contributes to applying common vocabulary, but such an
approach does not assist in constructing a foundation for a holistic security
methodology. We focus on defining the bounds and creating a representation of a
security system by developing a diagrammatic representation (i.e. a model) as a
means to describe computer network processes. The model, referred to a thinging
machine, is a first step toward developing a security strategy and plan. The
general aim is to demonstrate that the representation of the security system
plays a key role in making thinking visible through conceptual description of
the operational environment, a region in which active security operations are
undertaken. We apply the proposed model for email security by conceptually
describing a real email system.
