These abstracts are for talks at this event.
NEPLS is a venue for ongoing research, so the abstract and supplemental material associated with each talk is necessarily temporal. The work presented here may be in a state of flux. In all cases, please consult the authors' Web pages for up-to-date information. Please don't refer to these pages as a definitive source.
The Comet Programming Language and System
This talk gives an overview of the Comet system, a programming language designed to solve complex and large scale combinatorial optimization problems using local search. Comet integrates a small number of concepts from declarative and object-oriented programming which synergize to decrease the development time and the maintenance of these applications significantly. Of particular interest is the clean separation of concerns between modeling and search, and the high reusability promoted by Comet. This contrasts with the ad-hoc nature of most of these applications.
This is joint work with L. Michel. An early paper on Comet appeared in OOPSLA'02. See http://www.cs.brown.edu/people/pvh/oopsla02.ps.
Control Abstractions for Local Search Algorithms
Combinatorial optimization problems are ubiquitous in many practical applications. Yet most of them are challenging, both from computational complexity and programming standpoints. Local search is one of the main approaches to address these problems. However, it often requires sophisticated incremental algorithms and data structures, and considerable experimentation. Comet is a constraint-based, object-oriented, language and architecture that reduces the development time of local search algorithms significantly. The focus of the talk is a set of control abstractions that are essential to easily capture many complex search procedures. Control primitives and abstractions likes selectors, events, neighbors, continuations, states and checkpoints allow to separate orthogonal aspects of the search procedure and will be exemplified on code fragments drawn from applications like scheduling or routing. Joint work with Pascal Van Hentenryck, Brown University.
Automatic Detection and Repair of Errors in Data Structures
We present a system that accepts a specification of key data structure constraints, then dynamically detects and repairs violations of these constraints. Our approach involves two data structure views: a concrete view at the level of the bits in memory and an abstract view at the level of relations between abstract objects. The abstract view facilitates both the specification of higher level data structure constraints (especially constraints of linked data structures) and the reasoning required to repair any inconsistencies. Our experience using our system indicates that the specifications are relatively easy to develop once one understands the data structures. We have used our tool to repair inconsistencies in three applications: a simplified Linux file system, an interactive game, and Microsoft Word files. For this set of benchmark applications, our system can effectively repair errors to deliver consistent data structures that allow the program to continue to operate successfully within its designed operating envelope. In the absence of this repair, the programs usually failed. Our results therefore indicate that our technique may significantly enhance the ability of applications to recover from data structure errors. Joint work with Martin Rinard, MIT.
Our technical report describing this system may be found at http://www.lcs.mit.edu/publications/specpub.php?id=1656.
FLAVERS: A Finite State Verification Technique for Software Systems
Software systems are increasing in size and complexity and, subsequently, are becoming ever more difficult to validate. Finite State Verification (FSV) has been gaining credibility and attention as an alternative to testing and to formal verification approaches based on theorem proving. There has recently been a great deal of excitement about the potential for FSV approaches to prove properties about hardware descriptions but, for the most part, these approaches do not scale adequately to handle the complexity usually found in software. We have developed FLAVERS, an FSV approach that creates a compact and conservative, but imprecise, model of the system being analyzed, and then assists the analyst in adding additional details as guided by previous analysis results. We will describe the approach and discuss some experimental results demonstrating scalability. Contributors: Lori A. Clarke, Jamieson M. Cobleigh, Heather Conboy, Matthew B. Dwyer, Gleb Naumovich, Leon J. Osterweil, U. Mass Amherst.
A Typed representation for XML documents
When constructing programs for manipulating XML documents, we immediately face the question as to what internal representation should be chosen for XML documents so as to facilitate program construction. Currently, most representations used in practice are untyped in the sense that the type (DTD) of an XML document is not reflected in the type of its representation (if the representation is typed). In general, an untyped representation often involves the use of a great number of tags, which not only consumes space to store but also can incur tag checks at run-time. We propose a typed representation for XML documents that consists of a data part and a type part; the data part stores the data (but no tags) in a document while the type part stores the type (DTD) of the document. With this representation, we can not only save significant space when storing an XML document but also avoid run-time tag checks that would otherwise be needed when processing the document. More importantly, we can reap various software engineering benefits from typed programming in the first place.
This talk presents work done under the direction of Hongwei Xi. The details of this work can be found at http://cs-people.bu.edu/zhudp/pubs/XML-rep.html.
Hybrid Modelling with Automatic Differentiation and Impulses
Functional Reactive Programming (FRP) is a framework for reactive programming in a functional setting. FRP, in various incarnations, has been applied to a number of domains, such as graphical animation, graphical user interfaces, robotics, and computer vision. The latest member of the Yale FRP family of languages is called Yampa and is realized as an embedding in Haskell. Recently, we in the functional programming group at Yale have been interested in applying FRP-like ideas to hybrid modeling and simulation of physical systems, where our ultimate goal is a system where models can be expressed through non-directed equations, so called non-causal modeling. As a small step in that direction, we have adapted the technique of automatic differentiation to the present causal setting of Yampa, and extended it with a notion of Dirac impulses in order to deal correctly with certain classes of discontinuities in the models. This talk reviews the basic ideas behind automatic differentiation, in particular, Jerzy Karczmarczuk's elegant version for a lazy functional language with overloading, and then considers the integration with Yampa and with Dirac impulses.
Linguistic Side Effects
As a natural language semanticist, I strive to scientifically explain why "every student passed" entails "every diligent student passed", why "a man is mugged every 11 seconds" is ambiguous, and why "nobody asked any question" sounds better than "everybody asked any question". Making a linguistic theory is like specifying a programming language: one typically devises a type system to characterize what utterances are acceptable, and a denotational semantics to explain which statements entail which other ones. Along this connection, programming language research can inform linguistic theory and vice versa; in particular, computational side effects are intimately related to referential opacity in natural languages. In this talk, I will illustrate this link by using continuations and composable contexts to analyze quantification (as in "every student passed"). No prior knowledge of linguistics will be assumed. (This talk describes joint work with Chris Barker and Stuart Shieber.)
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