4 research outputs found
Revisiting causality, coalgebraically
In this paper we recast the classical Darondeau–Degano’s causal semantics of concurrency in a coalgebraic setting, where we derive a compact model. Our construction is inspired by the one of Montanari and Pistore yielding causal automata, but we show that it is instance of an existing categorical framework for modeling the semantics of nominal calculi, whose relevance is further demonstrated. The key idea is to represent events as names, and
the occurrence of a new event as name generation. We model causal semantics as a coalgebra
over a presheaf, along the lines of the Fiore–Turi approach to the semantics of nominal
calculi. More specifically, we take a suitable category of finite posets, representing causal
relations over events, and we equip it with an endofunctor that allocates new events and
relates them to their causes. Presheaves over this category express the relationship between
processes and causal relations among the processes’ events. We use the allocation operator to
define a category of well-behaved coalgebras: it models the occurrence of a new event along
each transition. Then we turn the causal transition relation into a coalgebra in this category,
where labels only exhibit maximal events with respect to the source states’ poset, and we
show that its bisimilarity is essentially Darondeau–Degano’s strong causal bisimilarity. This
coalgebra is still infinite-state, but we exploit the equivalence between coalgebras over a
class of presheaves and History Dependent automata to derive a compact representation,
where states only retain the poset of the most recent events for each atomic subprocess, and
are isomorphic up to order-preserving permutations. Remarkably, this reduction of states is
automatically performed along the equivalence
Decidability of Two Truly Concurrent Equivalences for Finite Bounded Petri Nets
We prove that (strong) fully-concurrent bisimilarity and causal-net bisimilarity are decidable for finite bounded Petri nets. The proofs are based on a generalization of the ordered marking proof technique that Vogler used to demonstrate that (strong) fully-concurrent bisimilarity (or, equivalently, historypreserving bisimilarity) is decidable on finite safe nets
“Why can’t I do that?”: tracing adaptive security decisions
One of the challenges of any adaptive system is to ensure that users can understand how and why the behaviour of the system changes at runtime. This is particularly important for adaptive security behaviours which are essential for applications that are used in many different contexts, such as those hosted in the cloud. In this paper, we propose an approach for using traceability information, enriched with causality relations and contextual attributes of the deployment environment, when providing feedback to the users. We demonstrate, using a cloud storage-as-a-service environment, how our approach provides users of cloud applications better information, explanations and assurances about the security decisions made by the system. This enables the user to understand why a certain security adaptation has occurred, how the adaptation is related to current context of use of the application, and a guarantee that the application still satisfies its security requirements after an adaptation
Decidability of Two Truly Concurrent Equivalences for Finite Bounded Petri Nets
We prove that the well-known (strong) fully-concurrent bisimilarity and the
novel i-causal-net bisimilarity, which is a sligtlhy coarser variant of
causal-net bisimilarity, are decidable for finite bounded Petri nets. The
proofs are based on a generalization of the ordered marking proof technique
that Vogler used to demonstrate that (strong) fully-concurrent bisimilarity
(or, equivalently, history-preserving bisimilarity) is decidable on finite safe
nets