AT&T Labs

About: AT&T Labs is a based out in . It is known for research contribution in the topics: Network packet & The Internet. The organization has 1879 authors who have published 5595 publications receiving 483151 citations.

On computing correlated aggregates over continual data streams

Abstract: In many applications from telephone fraud detection to network management, data arrives in a stream, and there is a need to maintain a variety of statistical summary information about a large number of customers in an online fashion. At present, such applications maintain basic aggregates such as running extrema values (MIN, MAX), averages, standard deviations, etc., that can be computed over data streams with limited space in a straightforward way. However, many applications require knowledge of more complex aggregates relating different attributes, so-called correlated aggregates. As an example, one might be interested in computing the percentage of international phone calls that are longer than the average duration of a domestic phone call. Exact computation of this aggregate requires multiple passes over the data stream, which is infeasible.We propose single-pass techniques for approximate computation of correlated aggregates over both landmark and sliding window views of a data stream of tuples, using a very limited amount of space. We consider both the case where the independent aggregate (average duration in the example above) is an extrema value and the case where it is an average value, with any standard aggregate as the dependent aggregate; these can be used as building blocks for more sophisticated aggregates. We present an extensive experimental study based on some real and a wide variety of synthetic data sets to demonstrate the accuracy of our techniques. We show that this effectiveness is explained by the fact that our techniques exploit monotonicity and convergence properties of aggregates over data streams.

Compact oracles for reachability and approximate distances in planar digraphs

Abstract: It is shown that a planar digraph can be preprocessed in near-linear time, producing a near-linear space oracle that can answer reachability queries in constant time. The oracle can be distributed as an O(log n) space label for each vertex and then we can determine if one vertex can reach another considering their two labels only.The approach generalizes to give a near-linear space approximate distances oracle for a weighted planar digraph. With weights drawn from l0, …, Nr, it approximates distances within a factor (1 + e) in O(log log (nN) + 1/e) time. Our scheme can be extended to find and route along correspondingly short dipaths.

Catching the boat with Strudel: experiences with a Web-site management system

Abstract: The Strudel system applies concepts from database management systems to the process of building Web sites. Strudel's key idea is separating the management of the site's data, the creation and management of the site's structure, and the visual presentation of the site's pages. First, the site builder creates a uniform model of all data available at the site. Second, the builder uses this model to declaratively define the Web site's structure by applying a “site-definition query” to the underlying data. The result of evaluating this query is a “site graph”, which represents both the site's content and structure. Third, the builder specifies the visual presentation of pages in Strudel's HTML-template language. The data model underlying Strudel is a semi-structured model of labeled directed graphs.We describe Strudel's key characteristics, report on our experiences using Strudel, and present the technical problems that arose from our experience. We describe our experience constructing several Web sites with Strudel and discuss the impact of potential users' requirements on Strudel's design. We address two main questions: (1) when does a declarative specification of site structure provide significant benefits, and (2) what are the main advantages provided by the semi-structured data model.

Appropriateness of the decision to transfer nursing facility residents to the hospital.

Abstract: OBJECTIVES: To develop and test a standardized instrument, the purpose of which is to assess (1) whether skilled nursing facilities (SNFs) transfer residents to emergency departments (ED) inappropriately, (2) whether residents are admitted to hospitals inappropriately, (3) and factors associated with inappropriate transfers. DESIGN: A structured implicit review (SIR) of medical records. SETTING AND PARTICIPANTS: Using nested random sampling in eight community SNFs, we identified SNF and hospital records of 100 unscheduled transfers to one of 10 hospitals. MEASUREMENTS: Seven trained physician reviewers assessed appropriateness using a SIR form designed for this study (2 independent reviews per record, 200 total reviews). We measured interrater reliability with kappa statistics and used bivariate analysis to identify factors associated with assessment that transfer was inappropriate. RESULTS: In 36% of ED transfers and 40% of hospital admissions, both reviewers agreed that transfer/admit was inappropriate, meaning the resident could have been cared for safely at a lower level of care. Agreement was high for both ED (percent agreement 84%, kappa .678) and hospital (percent agreement 89%, kappa .779). When advance directives were considered, both reviewers rated 44% of ED transfers and 45% of admissions inappropriate. Factors associated with inappropriateness included the perceptions that: (1) poor quality of care contributed to transfer need, (2) needed services would typically be available in outpatient settings, and (3) the chief complaint did not warrant hospitalization. CONCLUSIONS: Inappropriate transfers are a potentially large problem. Some inappropriate transfers may be associated with poor quality of care in SNFs. This study demonstrates that structured implicit review meets criteria for reliable assessment of inappropriate transfer rates. Structured implicit review may be a valuable tool for identifying inappropriate transfers from SNFs to EDs and hospitals. J Am Geriatr Soc 48: 154–163, 2000.