38159603
The COntext INterchange (COIN) Project: Data Extraction and Interpretation from Semi-Structured Web Sources
17041428
Context interchange in a client-server architecture
Abstract Many organizations today require information from diverse information systems, and government efforts are moving toward a national information infrastructure for sharing information. However, the systems used by these organizations lack the capabilities to meaningfully translate information among semantically heterogeneous environments. Because the meaning of data acquired from a source environment is usually different from that needed or expected in the receiver's environment, the effectiveness of information exchange is dependent on the system's capability for context interchange, i.e., the representation, exchange, comparison, and transformation of context knowledge. We show here a practical means for developing context interchange capabilities in a client-server architecture by use of semantic values (i.e., data and their context(as the unit of data exchange. The key components in this architecture are the context mediator server, whose job is to identify and construct the semantic values being sent, determine when the exchange is meaningful, and convert the semantic values to the form required by the client (i.e., receiver), and the data environment server, whose job is to assist in the location, access, development, and maintenance of the context knowledge for all clients and servers.
11984448
Context interchange: overcoming the challenges of large-scale interoperable database systems in a dynamic environment
Research in database interoperability has primarily focused on circumventing schematic and semantic incompatibility arising from autonomy of the underlying databases. We argue that, while existing integration strategies might provide satisfactory support for small or static systems, their inadequacies rapidly become evident in large-scale interoperable database systems operating in a dynamic environment. This paper highlights the problem of receiver heterogeneity, scalability, and evolution which have received little attention in the literature, provides an overview of the Context Interchange approach to interoperability, illustrates why this is able to better circumvent the problems identified, and forges the connections to other works by suggesting how the context interchange framework differs from other integration approaches in the literature.
9033123
Process Aggregation Using Web Services
This paper examines the opportunities and challenges related to data and process integration architectures in the context of Web Services. A primary goal of most enterprises in today's economic environment is to improve productivity by streamlining and aggregating business processes. This paper illustrates how integration architectures based on Web Services offer new opportunities to improve productivity that are expedient and economical. First, the paper introduces the technical standards associated with Web Services and provides business example for illustration. Abstracting from this example, we introduce a concept we call Process Aggregation that incorporates data aggregation and workflow to improve productivity. We show that Web Services will have a major impact on Process Aggregation, making it both faster and less expensive to implement. Finally, we suggest some research directions relating to the Process Aggregation challenges facing Web Services that are not currently being addressed by standards bodies or software vendors. These include context mediation, trusted intermediaries, quality and source selection, licensing and payment mechanisms, and systems development tools.
41563606
Conceptualizing Semantic Interoperability: A Perspective From the Knowledge Level
Currently, there is a proliferation of database integration approaches in response to the need to achieve semantic interoperability in heterogeneous, distributed and autonomous environments. To date, however, we lack abstract, formal descriptions of the task of semantic interoperation, independent of idiosyncratic implementation details. Such abstract descriptions are needed to aid our understanding of these various complex systems that are being constructed. Therefore, we argue that a knowledge level perspective of interoperable systems is desirable. The knowledge level serves as an abstract specification of what a system should do and facilitates the design and analysis of complex systems. In this paper, we show how an interoperable system, based on the Context Interchange Architecture, may be specified in terms of first-order logic which is an ideal specification language at the knowledge level. This specification represents a theoretical ideal which serves to formalize and communicate the key ideas behind the Context Interchange Approach, unencumbered by the details, limitations and compromises of specific implementations. As such, it provides a rigorous basis for implementing such systems. Similar specifications may also be developed for other models of interoperable systems. As a result, we have a rigorous means of understanding, comparing and analyzing these complex systems.
5563723
Data Integration Using Web Services
In this paper we examine the opportunities for data integration in the context of the emerging Web Services systems development paradigm. The paper introduces the programming standards associated with Web Services and provides an example of how Web Services can be used to unlock heterogeneous business systems to extract and integrate business data. We provide an introduction to the problems and research issues encountered when applying Web Services to data integration. We provide a formal definition of aggregation (as a type of data integration) and discuss the impact of Web Services on aggregation. We show that Web Services will make the development of systems for aggregation both faster and less expensive to develop. A system architecture for Web Services based aggregation is presented that is representative of products available from software vendors today. Finally, we highlight some of the challenges facing Web Services that are not currently being addressed by standards bodies or software vendors. These include context mediation, trusted intermediaries, quality and source selection, licensing and payment mechanisms, and systems development tools. We suggest some research directions for each of these challenges.
31386871
A Study of Singularity Formation in the Kelvin-Helmholtz Instability with Surface Tension
The possibility of singularity formation in vortex sheets acted on by surface tension is considered. In the evolution of a nearly flat vortex sheet with viscosity and surface tension neglected, Kelvin-Helmholtz instability has been shown to lead to the development of curvature singularities on the sheet. This is not unexpected, as the linearized equations of motion for this flow exhibit short-wavelength instability: infinitesimal perturbations grow at an infinite rate. Since the inclusion of surface tension stabilizes (on linear theory) the high-wavenumber modes, it has been presumed that it also suppresses the formation of singularities. The possibility of singularity formation is examined by generalizing Moore's approximation for vortex sheets to include the presence of surface tension. For the approximate theory, traveling wave solutions that develop singularities on the interface in finite time are found. Computations of the traveling wave solution are provided to reveal other features, and comparisons between these solutions and previously computed solutions of the full equations are made.
1155385
Implementing statecharts in PROMELA/SPIN
We translate statecharts into PROMELA, the input language of the SPIN verification system, using extended hierarchical automata as an intermediate format. We discuss two possible frameworks for this translation, leading to either sequential or parallel code. We show that in this context the sequential code can be verified more efficiently than the parallel code. We conclude with a discussion of an application of the resulting translator to a well-known case study, which demonstrates the feasibility of linear temporal logic model checking of statecharts.
122171625
The small model property: how small can it be?
Efficient decision procedures for equality logic (quantifier-free predicate calculus + the equality sign) are of major importance when proving logical equivalence between systems. We introduce an efficient decision procedure for the theory of equality based on finite instantiations. The main idea is to analyze the structure of the formula and compute accordingly a small domain to each variable such that the formula is satisfiable iff it can be satisfied over these domains. We show how the problem of finding these small domains can be reduced to an interesting graph theoretic problem. This method enabled us to verify formulas containing hundreds of integer and floating point variables that could not be efficiently handled with previously known techniques.
30791016
Extending the Limits of Sequentially Phased Reasoning
Verification via abstraction is the topic of concluding correctness of a complicated program from correctness of an abstraction of this program. Principles for sequentially phased reasoning are examples of verification via abstraction. They use permutation equivalences to abstract concurrent programs which logically work in phases to considerably simpler variants which perform these phases sequentially. It is shown in this paper that there are classes of concurrent programs, such as self-stabilizing ones, which logically work in phases but cannot be abstracted to a sequentialized version using permutation equivalence. A new class of so-called Ω-equivalences is defined which generalizes permutation equivalence and stutter equivalence. It is proved that both equivalences are indeed special cases of Ω-equivalences. A verification strategy based on Ω-equivalences is formulated and compared with existing approaches for sequentially phased reasoning. The strategy is applied to a self-stabilizing coloring program that can neither be abstracted by permutation nor by stutter equivalences to a sequentialized version.
8004380
A Well-Posed Numerical Method to Track Isolated Conformal Map Singularities in Hele-Shaw Flow
We present a new numerical method for calculating an evolving 2D Hele-Shaw interface when surface tension effects are neglected. In the case where the flow is directed from the less viscous fluid into the more viscous fluid, the motion of the interface is ill-posed; small deviations in the initial condition will produce significant changes in the ensuing motion. This situation is disastrous for numerical computation, as small roundoff errors can quickly lead to large inaccuracies in the computed solution. Our method of computation is most easily formulated using a conformal map from the fluid domain into a unit disk. The method relies on analytically continuing the initial data and equations of motion into the region exterior to the disk, where the evolution problem becomes well-posed. The equations are then numerically solved in the extended domain. The presence of singularities in the conformal map outside of the disk introduces specific structures along the fluid interface. Our method can explicitly track the location of isolated pole and branch point singularities, allowing us to draw connections between the development of interfacial patterns and the motion of singularities as they approach the unit disk. In particular, we are able to relate physical features such as finger shape, side-branch formation, and competition between fingers to the nature and location of the singularities. The usefulness of this method in studying the formation of topological singularities (self intersections of the interface) is also pointed out.