Security problems in collaborative work between multiple agencies are less well understood than those in the business and defence worlds. We develop a perspective for policies and models that is task-based on a need-to-know basis. These policies are represented by two protocols, the first CTCP (Collaboration Task-based Creation Protocol) dealing with negotiation, decision and agreement between the parties involved and the second CTRP (Collaboration Task-based Run-time Protocol) responsible for the operation of the policy. The two protocols and the relationship between them are defined in Petri-Nets. The overall model is formally defined using a categorical pullback construction. Each of the protocols, represented as Petri-Nets for statetransition purposes, is a category-valued functor in the pullback.
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