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.
33236770
Formal Verification of Stabilizing Systems
This paper links too formerly rather disjoint areas: formal verification and stabilization. Stabilization is a vitally emerging paradigm in fault tolerant distributed computing; formal verification investigates mathematically rigorous techniques to reason about systems.
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.
6836947
Deductive verification of stabilizing systems
17738680
Hierarchical Automata as Model for Statecharts
Statecharts are a very rich graphical specification formalism supported by the commercial tool Statemate. Statecharts comprises powerful concepts such as interlevel transitions, multiple-source/multiple-target transitions, priority amongst transitions and simultaneous execution of maximal non-conflicting sets of transitions. Every add-on tool which is supposed to be linked with the Statemate tool have to deal with the rather involved semantics of these concepts. We propose extended hierarchical automata as an intermediate format to facilitate the linking of new tools to the Statemate environment, whose main idea is to devise a simple formalism with a more restricted syntax than statecharts which nevertheless allows to capture the richer formalism. We define the format, give operational semantics to it, and translate statecharts to it.
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.
209098159
The Code Validation Tool CVT: Automatic Verification of a Compilation Process.
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.
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.
26524606
Automatic Rule Derivation For Semantic Query Optimization