179,319 research outputs found
AGM-consistency and perfect Bayesian equilibrium. Part I: definition and properties.
We provide a general notion of perfect Bayesian equilibrium which can be applied to arbitrary extensive-form games and is intermediate between subgame-perfect equilibrium and sequential equilibrium. The essential ingredient of the proposed definition is the qualitative notion of AGM-consistency, which has an epistemic justification based on the AGM theory of belief revision.belief revision, plausibility order, consistency, subgame-perfect equilibrium, sequential equilibrium, Bayesian updating.
Brief Announcement: Update Consistency in Partitionable Systems
Data replication is essential to ensure reliability, availability and
fault-tolerance of massive distributed applications over large scale systems
such as the Internet. However, these systems are prone to partitioning, which
by Brewer's CAP theorem [1] makes it impossible to use a strong consistency
criterion like atomicity. Eventual consistency [2] guaranties that all replicas
eventually converge to a common state when the participants stop updating.
However, it fails to fully specify shared objects and requires additional
non-intuitive and error-prone distributed specification techniques, that must
take into account all possible concurrent histories of updates to specify this
common state [3]. This approach, that can lead to specifications as complicated
as the implementations themselves, is limited by a more serious issue. The
concurrent specification of objects uses the notion of concurrent events. In
message-passing systems, two events are concurrent if they are enforced by
different processes and each process enforced its event before it received the
notification message from the other process. In other words, the notion of
concurrency depends on the implementation of the object, not on its
specification. Consequently, the final user may not know if two events are
concurrent without explicitly tracking the messages exchanged by the processes.
A specification should be independent of the system on which it is implemented.
We believe that an object should be totally specified by two facets: its
abstract data type, that characterizes its sequential executions, and a
consistency criterion, that defines how it is supposed to behave in a
distributed environment. Not only sequential specification helps repeal the
problem of intention, it also allows to use the well studied and understood
notions of languages and automata. This makes possible to apply all the tools
developed for sequential systems, from their simple definition using structures
and classes to the most advanced techniques like model checking and formal
verification. Eventual consistency (EC) imposes no constraint on the convergent
state, that very few depends on the sequential specification. For example, an
implementation that ignores all the updates is eventually consistent, as all
replicas converge to the initial state. We propose a new consistency criterion,
update consistency (UC), in which the convergent state must be obtained by a
total ordering of the updates, that contains the sequential order of eachComment: in DISC14 - 28th International Symposium on Distributed Computing,
Oct 2014, Austin, United State
A Joint Model for Definition Extraction with Syntactic Connection and Semantic Consistency
Definition Extraction (DE) is one of the well-known topics in Information
Extraction that aims to identify terms and their corresponding definitions in
unstructured texts. This task can be formalized either as a sentence
classification task (i.e., containing term-definition pairs or not) or a
sequential labeling task (i.e., identifying the boundaries of the terms and
definitions). The previous works for DE have only focused on one of the two
approaches, failing to model the inter-dependencies between the two tasks. In
this work, we propose a novel model for DE that simultaneously performs the two
tasks in a single framework to benefit from their inter-dependencies. Our model
features deep learning architectures to exploit the global structures of the
input sentences as well as the semantic consistencies between the terms and the
definitions, thereby improving the quality of the representation vectors for
DE. Besides the joint inference between sentence classification and sequential
labeling, the proposed model is fundamentally different from the prior work for
DE in that the prior work has only employed the local structures of the input
sentences (i.e., word-to-word relations), and not yet considered the semantic
consistencies between terms and definitions. In order to implement these novel
ideas, our model presents a multi-task learning framework that employs graph
convolutional neural networks and predicts the dependency paths between the
terms and the definitions. We also seek to enforce the consistency between the
representations of the terms and definitions both globally (i.e., increasing
semantic consistency between the representations of the entire sentences and
the terms/definitions) and locally (i.e., promoting the similarity between the
representations of the terms and the definitions)
Consistency Models with Global Operation Sequencing and their Composition
Modern distributed systems often achieve availability and scalability by providing consistency guarantees about the data they manage weaker than linearizability. We consider a class of such consistency models that, despite this weakening, guarantee that clients eventually agree on a global sequence of operations, while seeing a subsequence of this final sequence at any given point of time. Examples of such models include the classical Total Store Order (TSO) and recently proposed dual TSO, Global Sequence Protocol (GSP) and Ordered Sequential Consistency.
We define a unified model, called Global Sequence Consistency (GSC), that has the above models as its special cases, and investigate its key properties. First, we propose a condition under which multiple objects each satisfying GSC can be composed so that the whole set of objects satisfies GSC. Second, we prove an interesting relationship between special cases of GSC - GSP, TSO and dual TSO: we show that clients that do not communicate out-of-band cannot tell the difference between these models. To obtain these results, we propose a novel axiomatic specification of GSC and prove its equivalence to the operational definition of the model
Concurrent Reversible Sessions
We present a calculus for concurrent reversible multiparty sessions, which improves on recent proposals in several respects: it allows for concurrent and sequential composition within processes and types, it gives a compact representation of the past of processes and types, which facilitates the definition of rollback, and it implements a fine-tuned strategy for backward computation. We propose a refined session type system for our calculus and show that it enforces the expected properties of session fidelity, forward and backward progress, as well as causal consistency. In conclusion, our calculus is a conservative extension of previous proposals, offering enhanced expressive power and refined analysis techniques
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