We often learn of successful pedagogical experiments, but we seldom hear of the the ones that failed. For this special session we solicited submissions from the SIGCSE membership, selected the best from among these, and will have presentations at the session by the selected authors. Our contributions describe pedagogical approaches that seemed to be good ideas but turned out as failures. Contributors will describe their pedagogical experiment, the rationale for the experiment, evidence of failure, and lessons learned.

Research has reported that about 10% of Web searchers utilize advanced query operators, with the other 90% using extremely simple queries. It is often assumed that the use of query operators, such as Boolean operators and phrase searching, improves the effectiveness of Web searching. We test this assumption by examining the effects of query operators on the performance of three major Web search engines. We selected one hundred queries from the transaction log of a Web search service. Each of these original queries contained query operators such as AND, OR, MUST APPEAR (+), or PHRASE (" "). We then removed the operators from these one hundred advanced queries. We submitted both the original and modified queries to three major Web search engines; a total of 600 queries were submitted and 5,748 documents evaluated. We compared the results from the original queries with the operators to the results from the modified queries without the operators. We examined the results for changes in coverage, relative precision, and ranking of relevant documents. The use of most query operators had no significant effect on coverage, relative precision, or ranking, although the effect varied depending on the search engine. We discuss implications for the effectiveness of searching techniques as currently taught, for future information retrieval system design, and for future research.

Abstract Results of searches using a variety of query formulations with several Internet search engines show that strategies intended to give narrower and more precise results may not give improvements in precision even though they result in fewer hits. Searches were performed by students in graduate information retrieval courses using different formulations for the same topic.

No abstract available.

The node size that should be used in a hypermedia system is an important design issue. Three interpretations of node size are identified: storage (physical size), window size (presentation size), and length (logical size). An experiment in which presentation size and text length are varied in a HyperCard application is described. The experiment involves student subjects performing a fact retrieval task from a reference handbook. No interaction is found between these two independent variables. Performance is significantly better for the longer texts, but no significant difference is found for the two different window sizes.

A prototype system to handle negation in natural language queries to information retrieval systems is presented. Whenever a query that has negation is entered, the system will determine whether or not it is necessary for the user to clarify exactly what constituents in the query are being negated. If clarification is needed, the user is presented with a list of choices and asked to select the appropriate one. The algorithm used is based on the results of a survey administered to 64 subjects. The subjects were given a number of queries using negation. For each query, several possible choices for the negated constituent(s) were given. Whenever a lexical unit composed of nouns connected by the conjunction and was negated, there was general agreement on the response. But whenever there were multiple lexical units involved, such as complex lexical units connected by and or prepositional phrases, the subjects were divided on the choices. The results of this survey indicate that it is not possible for a system to automatically disambiguate all uses of negation. However, it is possible for the user interface to handle disambiguation through a clarification dialog during which a user is asked to select from a list of possible interpretations. © 1998 John Wiley & Sons, Inc.

Estimating the number of block accesses required to retrieve a set of records is an important problem in the design and implementation of data and knowledge systems. The models underlying some of the proposed estimation formulas are discussed as variations of occupancy problems, which have been extensively discussed in the literature in probability and statistics. Some additional properties of the relevant distributions are presented. In addition, an approach based on a sequential occupancy problem is discussed. This approach, which involves the estimation of the number of records which will require the retrieval of a target number of blocks, can be used to avoid the estimation of block accesses in some situations.

Queries containing negation are widely recognized as presenting problems for both users and systems. In information retrieval systems such problems usually manifest themselves in the use of the NOT operator. An algorithm to transform Boolean queries with negated terms into queries without negation is presented; the transformation process is based on the use of a hierarchical thesaurus. In addition, a set of user requests submitted to the Thomas Cooper Library at the University of South Carolina are examined to determine the pattern and frequency of use of negation. © 1990 John Wiley & Sons, Inc.

Approximate retrieval in a database of formatted data allows values that are close to those requested to be retrieved. Two approximate retrieval operators added to a structured query language are discussed. The two operators are sounds-like (SL) and close-to (CT). The SL operator is used to match two character string values by comparing their phonic sounds. The CT operator is used to select a subset of numeric data values that are relatively close to a given value. These two operators have been implemented and tested in a relational database environment called BDB. These extensions suffice to handle all data types and to allow the approximate retrieval to objects as well as attributes.>

Queries to information retrieval systems are often incrementally specified as a result of user interaction with the system. However, most discussions of file organizations consider only completely specified queries. The choice of file organizations to support such incremental specification is discussed qualitatively in this extended abstract. (Quantitative comparisons are partially complete and are not presented here.) Organizations which are advantageous for completely specified queries are not necessarily so for incrementally specified queries (and vice versa).

No abstract available.

The introductory course in computer science usually covers a mixture of topics. It generally includes an introduction to algorithms and problem solving, use of a particular programming language, basic concepts about computer systems, and use of the local computer system. This paper describes an organization of the introductory course, suitable for an interactive environment, which locates the control language coverage, which is dependent on the local computer system, in a separate course.

The problem of finding nearest neighbors to a query in a document collection is a special case of associative retrieval, in which searches are performed using more than one key. A nearest neighbors associative retrieval algorithm, suitable for document retrieval using similarity matching, is described. The basic structure used is a binary tree, at each node a set of keys (concepts) is tested to select the most promising branch. Backtracking to initially rejected branches is allowed and often necessary.