90,063 research outputs found
Boundedness in languages of infinite words
We define a new class of languages of -words, strictly extending
-regular languages.
One way to present this new class is by a type of regular expressions. The
new expressions are an extension of -regular expressions where two new
variants of the Kleene star are added: and . These new
exponents are used to say that parts of the input word have bounded size, and
that parts of the input can have arbitrarily large sizes, respectively. For
instance, the expression represents the language of infinite
words over the letters where there is a common bound on the number of
consecutive letters . The expression represents a similar
language, but this time the distance between consecutive 's is required to
tend toward the infinite.
We develop a theory for these languages, with a focus on decidability and
closure. We define an equivalent automaton model, extending B\"uchi automata.
The main technical result is a complementation lemma that works for languages
where only one type of exponent---either or ---is used.
We use the closure and decidability results to obtain partial decidability
results for the logic MSOLB, a logic obtained by extending monadic second-order
logic with new quantifiers that speak about the size of sets
Answering Regular Path Queries on Workflow Provenance
This paper proposes a novel approach for efficiently evaluating regular path
queries over provenance graphs of workflows that may include recursion. The
approach assumes that an execution g of a workflow G is labeled with
query-agnostic reachability labels using an existing technique. At query time,
given g, G and a regular path query R, the approach decomposes R into a set of
subqueries R1, ..., Rk that are safe for G. For each safe subquery Ri, G is
rewritten so that, using the reachability labels of nodes in g, whether or not
there is a path which matches Ri between two nodes can be decided in constant
time. The results of each safe subquery are then composed, possibly with some
small unsafe remainder, to produce an answer to R. The approach results in an
algorithm that significantly reduces the number of subqueries k over existing
techniques by increasing their size and complexity, and that evaluates each
subquery in time bounded by its input and output size. Experimental results
demonstrate the benefit of this approach
Expression-based aliasing for OO-languages
Alias analysis has been an interesting research topic in verification and
optimization of programs. The undecidability of determining whether two
expressions in a program may reference to the same object is the main source of
the challenges raised in alias analysis. In this paper we propose an extension
of a previously introduced alias calculus based on program expressions, to the
setting of unbounded program executions s.a. infinite loops and recursive
calls. Moreover, we devise a corresponding executable specification in the
K-framework. An important property of our extension is that, in a
non-concurrent setting, the corresponding alias expressions can be
over-approximated in terms of a notion of regular expressions. This further
enables us to show that the associated K-machinery implements an algorithm that
always stops and provides a sound over-approximation of the "may aliasing"
information, where soundness stands for the lack of false negatives. As a case
study, we analyze the integration and further applications of the alias
calculus in SCOOP. The latter is an object-oriented programming model for
concurrency, recently formalized in Maude; K-definitions can be compiled into
Maude for execution
Completing Queries: Rewriting of IncompleteWeb Queries under Schema Constraints
Reactive Web systems, Web services, and Web-based publish/
subscribe systems communicate events as XML messages, and in
many cases require composite event detection: it is not sufficient to react
to single event messages, but events have to be considered in relation to
other events that are received over time.
Emphasizing language design and formal semantics, we describe the
rule-based query language XChangeEQ for detecting composite events.
XChangeEQ is designed to completely cover and integrate the four complementary
querying dimensions: event data, event composition, temporal
relationships, and event accumulation. Semantics are provided as
model and fixpoint theories; while this is an established approach for rule
languages, it has not been applied for event queries before
Using parametric set constraints for locating errors in CLP programs
This paper introduces a framework of parametric descriptive directional types
for constraint logic programming (CLP). It proposes a method for locating type
errors in CLP programs and presents a prototype debugging tool. The main
technique used is checking correctness of programs w.r.t. type specifications.
The approach is based on a generalization of known methods for proving
correctness of logic programs to the case of parametric specifications.
Set-constraint techniques are used for formulating and checking verification
conditions for (parametric) polymorphic type specifications. The specifications
are expressed in a parametric extension of the formalism of term grammars. The
soundness of the method is proved and the prototype debugging tool supporting
the proposed approach is illustrated on examples.
The paper is a substantial extension of the previous work by the same authors
concerning monomorphic directional types.Comment: 64 pages, To appear in Theory and Practice of Logic Programmin
- …