An examination of PubMed's ability to disambiguate subject queries and journal title queries.

Term mapping in bibliographic databases optimizes user search results by matching a search term to an appropriate controlled vocabulary list. Term mapping in MEDLINE interfaces is not unusual [1]. PubMed's term-mapping system has evolved since its debut, but has consistently compared favorably to other MEDLINE search interfaces [2]. Two characteristics, employed through the query box, that contribute to its strength are its automatic application and the robustness of its mapping capabilities. Terms entered into PubMed's query box are automatically and seamlessly mapped to terms in one of several tables containing a controlled vocabulary list. It is not apparent to users that automatic term mapping is being applied to a search. An intuitive searcher may recognize that term mapping is being used by inferring from the search instructions located below the search query box or verify that it is used by clicking on the details button. In addition, information about term mapping can be obtained by pursuing the help links. PubMed's mapping system goes beyond Medical Subject Headings (MeSH) by employing four vocabulary-controlled mapping tables: MeSH Translation Table, Journals Translation Table, Phrase List, and Author Index. When no qualifiers are present in the search phrase, these four tables are applied sequentially. If a match is not found in the MeSH Translation Table, PubMed moves to the Journals Translation Table to look for a match, then to the Phrase List, and finally to the Author Index [3]. If no match is found the first time the mapping tables are applied, the phrase is broken apart into individual terms, from left to right, and the mapping table process is repeated. If a match cannot be found using the translation tables, each term in the phrase is searched individually as an All Fields keyword search and combined with a Boolean AND [4]. Single word journal titles are searched first in the MeSH Translation Table and secondly as an All Fields keyword search [5]. Stop words are ignored throughout the mapping and search process [6]. The application and use of these robust mapping tables are the foundations behind PubMed's single search point query box for subject, journal title, and author queries. Attention has been given in the literature to identifying and mapping journal title abbreviations to their full forms [7] and to mapping free-text to medical vocabularies [8]. Little attention has been given, however, to the methodology employed by search engines to disambiguate terms that could be construed as either a subject query or a journal title query. Given the correlation between entries in the MeSH Translation Table and journal titles, the disambiguation of whether a user intends to perform a subject query or a journal title query can be crucial to returning the appropriate search results. For example, a student searching for research articles on the topic of nutrition might search PubMed's query box using the following natural language search terms: “nutrition research.” PubMed's search engine would apply the search terms against its translation tables looking for a match. The search phrase “nutrition research” is not in the MeSH Translation Table and, therefore, would not find a match. The phrase would find a match in the subsequent Journals Translation Table since it is the title of a journal. As a result, the student who had intended to retrieve research articles on the topic of nutrition actually executed a journal title search on Nutrition Research. PubMed has established a set of rules governing journal title searching from the query box [9]. However, casual users would likely overlook PubMed's journal title search nuances, particularly when it interferes with an intended subject search. The implication of improper disambiguation of subject queries and journal title queries has the potential to mislead PubMed users. A closer look at this issue is warranted. The purpose of this study is to examine PubMed's ability to disambiguate subject searches and journal title searches.