The TREC-3 project at Virginia Tech focused on methods for combining the evidence from multiple retrieval runs and queries to improve retrieval performance over any single retrieval method or query. The largest improvements result from the combination of retrieval paradigms rather than from the use of multiple similar queries. 1 Overview The primary focus of our experiments at Virginia Tech involved methods of combining the results from various divergent search schemes and document collections. In performing our TREC-3 ad-hoc retrieval experiments on the provided test collections, the results from both vector and P-norm [3] queries were considered in estimating the similarity for each document in an individual collection. The results for each collection were then merged to create a single final set of documents that would be presented to the user. Our TREC-3 experiments built upon our TREC-2 experiments and focused more on determining where the improvements in combination were derived...

The use of inference networks to support document retrieval is introduced. A network-basead retrieval model is described and compared to conventional probabilis-tic and Boolean models. 1

The use of inference networks to support document retrieval is introduced. A network-based retrieval model is described and compared to conventional probabilistic and Boolean models. The performance of a retrieval system based on the inference network model is evaluated and compared to performance with conventional retrieval models,

It has been known that different representations of a query retrieve different sets of documents. Recent work suggests that significant improvements in retrieval performance can be achieved by combining multiple representations of an information need. However, little effort has been made to understand the reason why combining multiple sources of evidence improves retrieval effectiveness. In this paper we analyze why improvements can be achieved with evidence combination, and investigate how evidence should be combined. We describe a rationale for multiple evidence combination, and propose a combining method whose properties coincide with the rationale. We also investigate the effect of using rank instead of similarity on retrieval effectiveness. 1 Introduction A variety of representation techniques for queries and documents have been proposed in the information retrieval (IR) literature, and many corresponding retrieval techniques have also been developed to get higher retrieval effec...

Retrieval performance can often be improved significantly by using a number of different retrieval algorithms and combining the results, in contrast to using just a single retrieval algorithm. This is because different retrieval algorithms, or retrieval experts, often emphasize different document and query features when determining relevance and therefore retrieve different sets of documents. However, it is unclear how the different experts are to be combined, in general, to yield a superior overall estimate. We propose a method by which the relevance estimates made by different experts can be automatically combined to result in superior retrieval performance. We apply the method to two expert combination tasks. The applications demonstrate that the method can identify high performance combinations of experts and also is a novel means for determining the combined effectiveness of experts. 1 Introduction In text retrieval, two heads are definitely better than one. Retrieval performanc...

Three different types of classifiers were investigated in the context of a text categorization problem in the medical domain: the automatic assignment of ICD9 codes to dictated inpatient discharge summaries. K-nearest-neighbor, relevance feedback, and Bayesian independence classifers were applied individually and in combination. A combination of different classifiers produced better results than any single type of classifier. For this specific medical categorization problem, new query formulation and weighting methods used in the k-nearest-neighbor classifier improved performance. 1 Introduction Past research in information retrieval has shown that one can improve retrieval effectiveness by using multiple representations in indexing and query formulation [27] [19] [3] [11] and by using multiple search strategies [5] [24] [7]. In this work, we investigate whether we can attain similar improvements in the domain of text categorization by combining different representations and classif...

Abstract-We report on two studies in the TREC-2 program that investigated the effect on retrieval performance of combination of multiple representations of TREC topics. In one of the projects, five separate Boolean queries for each of the 50 TREC routing topics and 25 of the TREC ad hoc topics were generated by 75 experienced online searchers. Using the INQUERY retrieval system, these queries were both combined into single queries, and used to produce five separate retrieval results for each topic. In the former case, progressive combination of queries led to progressively improving retrieval performance, significantly better than that of single queries, and at least as good as the best individual single-query formulations. In the latter case, data fusion of the ranked lists also led to performance better than that of any single list. In the second project, two automatically produced vector queries and three versions of a manually produced P-norm extended Boolean query for each routing and ad hoc topic were compared and combined. This project investigated six different methods of combination of queries, and the combination of the same queries on different databases. As in the first project, progressive combination led to progressively improving results, with the best results, on average, being achieved by combination through summing of retrieval status values. Both projects found that the best method of combination often led to results that were better than the best performing single query. The combined results from the two projects have also been combined by data fusion. The results of this procedure show that combining evidence from completely different systems also leads to performance improvement. 1.

The objective of the paper is to amalgamate theories of text retrieval from various research traditions into a cognitive theory for information retrieval interaction. Set in a cognitive framework, the paper outlines the concept of polyrepresentation applied to both the user's cognitive space and the information space of IR systems. The concept seeks to represent the current user's information need, problem state, and domain work task or interest in a structure of causality. Further, it implies that we should apply different methods of representation and a variety of IR techniques of different cognitive and functional origin simultaneously to each semantic full-text entity in the information space. The cognitive differences imply that by applying cognitive overlaps of information objects, originating from different interpretations of such objects through time and by type, the degree of uncertainty inherent in IR is decreased. Polyrepresentation and the use of cognitive overlaps are associated with, but not identical to, data

Five independently generated Boolean query formulations for ten different TREC topics were produced by ten different expert online searchers. These different formulations were grouped, and the groups, and combinations of them, were used as searches against the TREC test collection, using the INQUERY probabilistic inference network retrieval engine. Results show that progressive combination of query formulations leads to progressively improving retrieval performance. Results were compared against the performance of INQUERY natural language based queries, and in combination with them. The issue of recall as a performance measure in large databases was raised, since overlap between the searches conducted in this study, and the TREC-1 searches, was smaller than expected.

The combination of different text representations and search strategies has become a standard technique for improving the effectiveness of information retrieval. Combination, for example, has been studied extensively in the TREC evaluations and is the basis of the “meta-search” engines used on the Web. This paper examines the development of this technique, including both experimental results and the retrieval models that have been proposed as formal frameworks for combination. We show that combining approaches for information retrieval can be modeled as combining the outputs of multiple classifiers based on one or more representations, and that this simple model can provide explanations for many of the experimental results. We also show that this view of combination is very similar to the inference net model, and that a new approach to retrieval based on language models supports combination and can be integrated with the inference net model.