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.
523278
Seizing the Opportunity: Exploiting Web Aggregation
This paper examines the development of web aggregators, entities that collect information from a wide range of sources, with or without prior arrangements, and add value through post-aggregation services. New Web-page extraction tools, context sensitive mediators, and agent technologies have greatly reduced the barriers to constructing aggregators. We predict that aggregators will soon emerge in industries where they were not formerly present. Through studying over a hundred existing and emerging aggregators, we present a model for understanding the aggregator's strategic interaction with existing organizations. We also suggest different ways that businesses can take advantage of the new opportunities presented. Finally, we provide valuable insights to all organizations concerning the issues, impacts, and actions required as aggregators become increasingly present.
17058444
The Context Interchange Network Prototype
In this paper we describe a prototype implementation of the Context Interchange Network (CIN). The prototype is described in terms of a financial application. The CIN is designed to provide for the intelligent integration of contextually (i.e., semantically) heterogeneous data. The system uses explicit context knowledge representation and a context mediator to automatically detect conflicts and resolve them through context conversion. The network also allows for context explication; making it possible for a receiver of data to understand meaning of the information represented by the source data.
2677077
Context interchange: new features and formalisms for the intelligent integration of information
The Context Interchange strategy presents a novel perspective for mediated data access in which semantic conflicts among heterogeneous systems are not identified a priori, but are detected and reconciled by a context mediator through comparison of contexts axioms corresponding to the systems engaged in data exchange. In this article, we show that queries formulated on shared views, export schema, and shared “ontologies” can be mediated in the same way using the Context Interchange framework. The proposed framework provides a logic-based object-oriented formalsim for representing and reasoning about data semantics in disparate systems, and has been validated in a prototype implementation providing mediated data access to both traditional and web-based information sources.
9548963
Using semantic values to facilitate interoperability among heterogeneous information systems
Large organizations need to exchange information among many separately developed systems. In order for this exchange to be useful, the individual systems must agree on the meaning of their exchanged data. That is, the organization must ensure semantic interoperability. This paper provides a theory of semantic values as a unit of exchange that facilitates semantic interoperability betweeen heterogeneous information systems. We show how semantic values can either be stored explicitly or be defined by environments. A system architecture is presented that allows autonomous components to share semantic values. The key component in this architecture is called the context mediator, whose job is to identify and construct the semantic values being sent, to determine when the exchange is meaningful, and to convert the semantic values to the form required by the receiver.
Our theory is then applied to the relational model. We provide an interpretation of standard SQL queries in which context conversions and manipulations are transparent to the user. We also introduce an extension of SQL, called Context-SQL (C-SQL), in which the context of a semantic value can be explicitly accessed and updated. Finally, we describe the implementation of a prototype context mediator for a relational C-SQL system.
5683523
A Metadata Approach to Resolving Semantic Conflicts
In this paper we describe a rule-based approach to semantic specification that can be used to establish semantic agreement between a source and receiver. Query processing techniques use these specifications along with conversion routines and query modification to guarantee correct data semantics. This work also examines the effect of changing data semantics. These changes may occur at the source of the data or they may be changes in the specifications of the dat,a semantics for the application, Methods are described for detecting these changes and for determining if the database can continue to supply meaningful data to the application. These methods for semanlic reconcilia2ion are necessary for determining logical connectivity between a data source (database) and a data receiver (application). Though described in terms of the source-receiver model, these techniques can also be used for semantic reconciliation and schema integration for multidatabase systems. Keywords[data dictionaries, heterogeneous databases, metadata, query modification, schema integration, semantic conflicts]
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.
37254437
Exact Solutions for the Evolution of a Bubble in Stokes Flow: A Cauchy Transform Approach
A Cauchy transform approach to the problem of determining the free surface evolution of a single bubble in Stokes flow is developed. A number of exact solutions to a class of problems have been derived in the literature using conformal mapping theory, and these solutions are retrieved and further generalized using the new formulation. Certain quantities which are conserved by the dynamics are also identified, the existence of which had not previously been pointed out. A principal purpose of this paper is to use the new formulation to understand when it is possible to externally specify the evolution of the bubble area in such classes of exact solution. It is found to be possible only for certain types of far-field boundary conditions.
15882359
Deciding Equality Formulas by Small Domains Instantiations
We introduce an efficient decision procedure for the theory of equality based on finite instantiations. When using the finite instantiations method, it is a common practice to take a range of [1..n] (where n is the number of input non-Boolean variables) as the range for all non-Boolean variables, resulting in a state-space of nn. Although various attempts to minimize this range were made, typically they either required various restrictions on the investigated formulas or were not very effective. In many cases, the nn state-space cannot be handled by BDD-based tools within a reasonable amount of time. In this paper we show that significantly smaller domains can be algorithmically found, by analyzing the structure of the formula. We also show an upper bound for the state-space based on this analysis. This method enabled us to verify formulas containing hundreds of integer and floating point variables.
39950733
A Refinement Theory that Supports both 'Decrease of Nondeterminism' and 'Increase of Parallelism'
The decrease of nondeterminism development paradigm that underlies most refinement approaches for concurrent systems is contrasted with the less studied increase of parallelism paradigm used by many protocol designers. We show that the widely used refinement notion of Abadi & Lamport exclusively supports the first paradigm and formulate a generalization that allows derivations of systems applying both paradigms alternatively. We develop the proof technique delayed simulation to prove Abadi & Lamport refinement and its generalization.
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.