11 research outputs found
On Tools for Completeness of Kleene Algebra with Hypotheses
In the literature on Kleene algebra, a number of variants have been proposed
which impose additional structure specified by a theory, such as Kleene algebra
with tests (KAT) and the recent Kleene algebra with observations (KAO), or make
specific assumptions about certain constants, as for instance in NetKAT. Many
of these variants fit within the unifying perspective offered by Kleene algebra
with hypotheses, which comes with a canonical language model constructed from a
given set of hypotheses. For the case of KAT, this model corresponds to the
familiar interpretation of expressions as languages of guarded strings. A
relevant question therefore is whether Kleene algebra together with a given set
of hypotheses is complete with respect to its canonical language model. In this
paper, we revisit, combine and extend existing results on this question to
obtain tools for proving completeness in a modular way. We showcase these tools
by giving new and modular proofs of completeness for KAT, KAO and NetKAT, and
we prove completeness for new variants of KAT: KAT extended with a constant for
the full relation, KAT extended with a converse operation, and a version of KAT
where the collection of tests only forms a distributive lattice
Kleene Algebra with Observations
Kleene algebra with tests (KAT) is an algebraic framework for reasoning about the control flow of sequential programs. Generalising KAT to reason about concurrent programs is not straightforward, because axioms native to KAT in conjunction with expected axioms for concurrency lead to an anomalous equation. In this paper, we propose Kleene algebra with observations (KAO), a variant of KAT, as an alternative foundation for extending KAT to a concurrent setting. We characterise the free model of KAO, and establish a decision procedure w.r.t. its equational theory
Concurrent Kleene Algebra with Observations: from Hypotheses to Completeness
Concurrent Kleene Algebra (CKA) extends basic Kleene algebra with a parallel
composition operator, which enables reasoning about concurrent programs.
However, CKA fundamentally misses tests, which are needed to model standard
programming constructs such as conditionals and -loops. It
turns out that integrating tests in CKA is subtle, due to their interaction
with parallelism. In this paper we provide a solution in the form of Concurrent
Kleene Algebra with Observations (CKAO). Our main contribution is a
completeness theorem for CKAO. Our result resorts on a more general study of
CKA "with hypotheses", of which CKAO turns out to be an instance: this analysis
is of independent interest, as it can be applied to extensions of CKA other
than CKAO
Towards an analysis of dynamic gossip in NetKAT
In this paper we analyse the dynamic gossip problem using the algebraic network programming language Netkat. Netkat is a language based on Kleene algebra with tests and describes packets travelling through networks. It has a sound and complete axiomatisation and an efficient coalgebraic decision procedure. Dynamic gossip studies how information spreads through a peer-to-peer network in which links are added dynamically. In this paper we embed dynamic gossip into Netkat. We show that a reinterpretation of Netkat in which we keep track of the state of switches allows us to model Learn New Secrets, a well-studied protocol for dynamic gossip. We axiomatise this reinterpretation of Netkat and show that it is sound and complete with respect to the packet-processing model, via a translation back to standard Netkat. Our main result is that many common decision problems about gossip graphs can be reduced to checks of Netkat equivalences. We also implemented the reduction
Completeness Theorems for Kleene Algebra with Top
We prove two completeness results for Kleene algebra with a top element, with respect to languages and binary relations. While the equational theories of those two classes of models coincide over the signature of Kleene algebra, this is no longer the case when we consider an additional constant "top" for the full element. Indeed, the full relation satisfies more laws than the full language, and we show that those additional laws can all be derived from a single additional axiom. We recover that the two equational theories coincide if we slightly generalise the notion of relational model, allowing sub-algebras of relations where top is a greatest element but not necessarily the full relation. We use models of closed languages and reductions in order to prove our completeness results, which are relative to any axiomatisation of the algebra of regular events
Completeness Theorems for Kleene Algebra with Top
International audienceWe prove two completeness results for Kleene algebra with a top element, with respect to languages and binary relations. While the equational theories of those two classes of models coincide over the signature of Kleene algebra, this is no longer the case when we consider an additional constant "top" for the full element. Indeed, the full relation satisfies more laws than the full language, and we show that those additional laws can all be derived from a single additional axiom. We recover that the two equational theories coincide if we slightly generalise the notion of relational model, allowing sub-algebras of relations where top is a greatest element but not necessarily the full relation. We use models of closed languages and reductions in order to prove our completeness results, which are relative to any axiomatisation of the algebra of regular events
Completeness Theorems for Kleene Algebra with Top
International audienceWe prove two completeness results for Kleene algebra with a top element, with respect to languages and binary relations. While the equational theories of those two classes of models coincide over the signature of Kleene algebra, this is no longer the case when we consider an additional constant "top" for the full element. Indeed, the full relation satisfies more laws than the full language, and we show that those additional laws can all be derived from a single additional axiom. We recover that the two equational theories coincide if we slightly generalise the notion of relational model, allowing sub-algebras of relations where top is a greatest element but not necessarily the full relation. We use models of closed languages and reductions in order to prove our completeness results, which are relative to any axiomatisation of the algebra of regular events
On Tools for Completeness of Kleene Algebra with Hypotheses
International audienceIn the literature on Kleene algebra, a number of variants have been proposed which impose additional structure specified by a theory, such as Kleene algebra with tests (KAT) and the recent Kleene algebra with observations (KAO), or make specific assumptions about certain constants, as for instance in NetKAT. Many of these variants fit within the unifying perspective offered by Kleene algebra with hypotheses, which comes with a canonical language model constructed from a given set of hypotheses. For the case of KAT, this model corresponds to the familiar interpretation of expressions as languages of guarded strings. A relevant question therefore is whether Kleene algebra together with a given set of hypotheses is complete with respect to its canonical language model. In this paper, we revisit, combine and extend existing results on this question to obtain tools for proving completeness in a modular way. We showcase these tools by reproving completeness of KAT and KAO, and prove completeness of a new variant of KAT where the collection of tests only forms a distributive lattice
Towards an Analysis of Dynamic Gossip in Netkat
In this paper we analyse the dynamic gossip problem using the algebraic network programming language Netkat. Netkat is a language based on Kleene algebra with tests and describes packets travelling through networks. It has a sound and complete axiomatisation and an efficient coalgebraic decision procedure. Dynamic gossip studies how information spreads through a peer-to-peer network in which links are added dynamically. In this paper we embed dynamic gossip into Netkat. We show that a reinterpretation of Netkat in which we keep track of the state of switches allows us to model Learn New Secrets, a well-studied protocol for dynamic gossip. We axiomatise this reinterpretation of Netkat and show that it is sound and complete with respect to the packet-processing model, via a translation back to standard Netkat. Our main result is that many common decision problems about gossip graphs can be reduced to checks of Netkat equivalences. We also implemented the reduction