Type Systems for Distributed Programs: Components and Sessions

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We show details of these tests and discuss possible explanations for this phenomenon. As computing times on massively-parallel clusters are expensive, we consider it especially interesting to share these kind of experimental results. Over the past decades we have developed formal frameworks to refine specifications into more detailed representations. These handle both deterministic and probabilistic specifications. We also have developed means for relaxing formality when the occasion demands it retrenchment.

I will pay particular attention to quantum artifacts, e. Such approaches generally work by 'homing in' on an appropriate program, using deviation of results from specified results as guidance. This can produce programs that are either right or nearly right. I'll do a round trip with evolutionary computation and indicate the use of GP in unearthing formal specification fragments from test traces for traditional programs using mutation approaches to get rid of uninteresting potential invariants inferred.

General-purpose program synthesizers face a tradeoff between having a rich vocabulary for output programs and the time taken to discover a solution. One performance bottleneck is the construction of a space of possible output programs that is both expressive and easy to search. In this paper we achieve both richness and scalability using a new algorithm for constructing symbolic syntax graphs out of easily specified components to represent the space of output programs. Our algorithm ensures that any program in the space is type-safe and only mutates values that are explicitly marked as mutable.

It also shares structure where possible and encodes programs in a straight-line format instead of the typical bushy-tree format, which gives an inductive bias towards realistic programs. These optimizations shrink the size of the space of programs, leading to more efficient synthesis, without sacrificing expressiveness. We evaluate our algorithm on a suite of benchmarks and show that it performs significantly better than prior work.

We study possibilities of using symbol elimination in program verification and synthesis. We consider programs in which some instructions or subprograms are not fully specified; the task is to derive conditions on the parameters or subprograms which imply inductivity of certain properties. We then propose a method for property-directed invariant generation and analyze its properties.

Binary Session Types in Coq (BEHAPI Workshop on Behavioural APIs) - ETAPS

Programming by example PBE is a powerful programming paradigm based on example driven synthesis. Users can provide examples, and a tool automatically constructs a program that satisfies the examples. To investigate the impact of PBE on real-world users, we built a study around StriSynth, a tool for shell scripting by example, and recruited 27 working IT professionals to participate.

In our study, we asked the users to complete three tasks with StriSynth, and the same three tasks with PowerShell, a traditional scripting language.

Stateful Session EJB Part 2

We found that, although our participants completed the tasks more quickly with StriSynth, they reported that they believed PowerShell to be a more helpful tool. The transformations we consider are expressed using deterministic finite automata DFA that read pairs of letters, one letter from the input and one from the output.

The DFA corresponding to these transformations have additional constraints, ensuring that each input string is mapped to exactly one output string. We therefore study the problem of, given a set of examples, finding a minimal DFA consistent with the examples and satisfying the functionality and totality constraints mentioned above. We prove that, in general, this problem the corresponding decision problem is NP-complete. This is unlike the standard DFA minimization problem which can be solved in polynomial time.

We provide several NP-hardness proofs that show the hardness of multiple independent variants of the problem. We implemented the algorithm, and used it to evaluate the likelihood that the minimal DFA indeed corresponds to the DFA expected by the user. The tutorial will also shed light on what has been done under the hood so far to scale TLC to modern day hardware and what we are up to next to tackle the state space explosion challenge.

Proving lemmas in synthetic geometry is an often time-consuming endeavour - many intermediate lemmas need to be proven before interesting results can be obtained. Automated theorem provers ATP made much progress in the recent years and can prove many of these intermediate lemmas automatically. The interactive theorem prover Elfe accepts mathematical texts written in fair English and verifies the text with the help of ATP. Geometrical texts can thereby easily be formalized in Elfe, leaving only the cornerstones of a proof to be derived by the user.

This allows for teaching axiomatic geometry to students without prior experience in formal mathematics.

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We present a new succinct proof of the uncountability of the real numbers — optimized for clarity — based on the proof by Benjamin Porter in the Isabelle Analysis theory. But achieving impact ultimately requires an understanding of the engineering context in which the tools will be deployed. Based on our tried-and-trusted methods of high-integrity software development at Altran, I will identify key features of the industrial landscape in which software verification tools have to operate, and some of the pitfalls that can stop them being adopted, including regulation, qualification, scalability, cost justification, and the overall tool ecosystem.

The talk will conclude by drawing some key lessons that can be applied to avoid the traps and pitfalls that tools encounter on their journey to succesful deployment. We introduce a new framework for verifying electronic vote counting results that are based on the Single Transferable Vote scheme STV. Our approach frames electronic vote counting as certified computation where each execution of the counting algorithm is accompanied by a certificate that witnesses the correctness of the output. These certificates are then checked for correctness independently of how they are produced.

We advocate to verify the verifier rather than the soft- ware used to produce the result. We use the theorem prover HOL to formalise the STV vote counting scheme, and obtain a fully verified certificate checker. By connecting HOL with the verified CakeML compiler, we then extract an executable that is guaranteed to behave correctly with respect to the formal specification of the protocol down to machine level.

We demonstrate that our verifier can check certificates of real-size elections efficiently.

Type Systems for Distributed Programs: Components and Sessions

Our encoding is modular, so repeating the same pro- cess for another different STV scheme would require a minimal amount of additional work. Developing advanced robotics and autonomous applications is now facing the confidence issue for their acceptability in everyday life. This confidence could be justified by the use of dependability techniques as it is done in other safety-critical applications. However, due to specific robotic properties such as continuous physical interaction or non-deterministic decisional layer , many techniques need to be adapted or revised.

This presentation will introduce these major issues for autonomous systems, and focus on current research work at LAAS in France, on model-based risk analysis for physical human-robot interactions, active safety monitoring for autonomous systems, and testing in simulation of mobile robot navigation. In this demo, we will illustrate our work on integrating formal verification techniques, in particular probabilistic model checking, to enable long term deployments of mobile service robots in everyday environments. Our framework is based on generating policies for Markov decision process MDP models of mobile robots, using co-safe linear temporal logic specifications.

More specifically, we build MDP models of robot navigation and action execution where the probability of successfully navigating between two locations and the expected time to do so are learnt from experience. For a specification over these models, we maximise the probability of the robot satisfying it, and minimise the expected time to do so. The policy obtained for this objective can be seen as a robot plan with attached probabilistic performance guarantees. Our proposal is to showcase this framework live during the workshop, deploying our robot in the workshop venue and having it perform tasks throughout the day the robot is based in the Oxford Robotics Institute, hence it can be easily moved to the workshop venue.

In conjunction with showing the live robot behaviour, we will, among other things, provide visualisation of the generated policies on a map of the environment; showcase how the robot keeps track of the performance guarantees calculated offline during policy execution; and show how these guarantees can be used for execution monitoring. We present an extension of the Kachinuki order on strings. The Kachinuki order transforms the problem of comparing strings to the problem of comparing their syllables length-lexicographically, where the syllables are defined via a precedence on the alphabet.

Our extension allows the number of syllables to increase under rewriting, provided we bound it by a weakly compatible interpretation.


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Weight functions are among the simplest methods for proving termination of string rewrite systems, and of rather limited applicability. In this working paper, we propose a generalized approach.


  1. Basic Semantics!
  2. Mutuality : the vision of Martin Buber;
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  4. As a first step, syllable decomposition yields a transformed, typically infinite rewrite system over an infinite alphabet, as the title indicates. Combined with generalized weight functions, termination proofs become feasible also for systems that are not necessarily simply terminating.

    sfplatform30nick.dev3.develag.com The method is limited to systems with linear derivational complexity, however, and this working paper is restricted to original alphabets of size two. The proof principle is almost self-explanatory, and if successful, produces simple proofs with short proof certificates, often even shorter than the problem instance. A prototype implementation was used to produce nontrivial examples. We prove that operational termination of declarative programs can be characterized by means of well-founded relations between specific formulas which can be obtained from the program.

    We show how to generate such relations by means of logical models where the interpretation of some binary predicates are required to be well-founded relations. Such logical models can be automatically generated by using existing tools. This provides a basis for the implementation of tools for automatically proving operational termination of declarative programs.

    Propositional logic is the main ingredient used to build up SAT solvers which have gradually become powerful tools to solve a variety of important and complicated problems such as planning, scheduling, and verifications. However further uses of these solvers are subject to the resulting complexity of transforming counting constraints into conjunctive normal form CNF. This transformation leads, generally, to a substantial increase in the number of variables and clauses, due to the limitation of the expressive power of propositional logic.

    To overcome this drawback, this work extends the alphabet of propositional logic by including the natural numbers as a means of counting and adjusts the underlying language accordingly.

    Reward Yourself

    The resulting representational formalism, called pseudo-propositional logic, can be viewed as a generalization of propositional logic where counting constraints are naturally formulated, and the generalized inference rules can be as easily applied and implemented as arithmetic.

    Classical logics are explosive -- from a contradiction everything follows. This is problematic e. In paraconsistent logics everything does not follow from a contradiction.