29720896
Assessing data quality for information products
Data quality is a critical issue in the design and implementation of databases. Often, the information provided to decision-makers is derived from heterogeneous databases. To determine the quality characteristics of information provided to decision-makers (derived data), it is necessary to determine how quality characteristics associated with diverse data sources affect the quality of the derived data. We discuss a methodology to determine two data quality characteristics, accuracy and incompleteness, that are of critical importance to decision-makers. We examine how the quality metrics of source data affect metrics for data derived using relational algebra operations.
476243
Reconciling Attribute Values from Multiple Data Sources
Because of the heterogeneous nature of multiple data sources, data integration is often one of the most challenging tasks of today’s information systems. While the existing literature has focused on problems such as schema integration and entity identification, our current study attempts to answer a basic question: When an attribute value for a real-world entity is recorded differently in two databases, how should the “best” value be chosen from the set of possible values? We first show how probabilities for attribute values can be derived, and then propose a framework for deciding the cost-minimizing value based on the total cost of type I, type II, and misrepresentation errors.
28618041
Availability of a periodically inspected system, maintained under an imperfect-repair policy
A periodically inspected system is maintained through a fixed number of imperfect-repairs before being replaced or perfectly repaired. The lifetime distribution of the system in its new and imperfectly repaired states is arbitrary. The times required for imperfect repairs and for perfect repair or replacement are random. The repaired system is restored to operation at the next scheduled inspection time. The system availability function is expressed as the weighted average of the survival functions and their shifts, and gives the limiting average availability.
27571789
Computation of intraprocedural dynamic program slices
Abstract Dynamic slicing algorithms are used in interactive applications such as program debugging and testing. Therefore, these algorithms need to be very efficient. In this context, we propose three intraprocedural dynamic slicing algorithms which are more space and time efficient than the existing algorithms. Two of the proposed algorithms compute precise dynamic slices of structured programs using Program Dependence Graph as an intermediate representation. To compute precise dynamic slices of unstructured programs, we introduce the concepts of jump dependence and Unstructured Program Dependence Graph. The third algorithm uses Unstructured Program Dependence Graph as the intermediate program representation, and computes precise dynamic slices of unstructured programs. We show that each of our proposed algorithms is more space and time efficient than the existing algorithms.
1183276
Effective Use of Memory in Iterative Deepening Search
Abstract The Iterative Deepening A∗ (IDA∗) (R.E. Korf, Artificial Intelligence 27 (1985)) algorithm often reexpands too many nodes while solving certain combinatorial problems. Algorithm IDA∗_CR (U.K. Sarkar, Artificial Intelligence 50 (1991)) attempted to remedy this drawback. These algorithms require very little memory although much more is available in practice. This paper introduces an algorithm IDA∗_CRM which shows how the available memory can be advantageously utilized in IDAast;_CR in order to reduce the number of expanded nodes. IDA∗_CRAM, an approximation scheme derived from IDA∗_CRM, is also presented. Computational results are shown for the Flow-Shop Scheduling Problem.
1395675
Small Proof Witnesses for LF
We instrument a higher-order logic programming search procedure to generate and check small proof witnesses for the Twelf system, an implementation of the logical framework LF. In particular, we extend and generalize ideas from Necula and Rahul [16] in two main ways: 1) We consider the full fragment of LF including dependent types and higher-order terms and 2) We study the use of caching of sub-proofs to further compact proof representations. Our experimental results demonstrate that many of the restrictions in previous work can be overcome and generating and checking small witnesses within Twelf provides valuable addition to its general safety infrastructure.
5653745
Foundational Certified Code in a Metalogical Framework
Foundational certified code systems seek to prove untrusted programs to be safe relative to safety policies given in terms of actual machine architectures, thereby improving the systems’ flexibility and extensibility. Previous efforts have employed a structure wherein the proofs are expressed in the same logic used to express the safety policy. We propose an alternative structure wherein safety proofs are expressed in the Twelf metalogic, thereby eliminating from those proofs an extra layer of encoding needed in the previous accounts. Using this metalogical approach, we have constructed a complete, foundational account of safety for a fully expressive typed assembly language.