The Citation Index as a Search Tool

The introduction of SC1 in 1964 was the first large-scale attempt to apply the citation-indexing concept to the problem of searching the scientific literature. Unfamiliar and unconventional as SC1 was in terms of its organization and search methodology, it established itself rather quickly as an important literature-retrieval tool: librarians and scientists found that it identified a high percentage of the material published on a given subject and that a high percentage of what it identified was pertinent. While many factors account for the rapid adoption of SC& the most significant is the Citation Index and its use of reference citations as indexing terms. That single feature gives a citation index three unique functional characteristics that have a significant impact on search productivity and efficiency (see Chapter One). The first is a subject categorization of published material that is, semantically, both more precise and detailed. It is also semantically more stable and flexible than conventional subject indexing. The other two characteristics are a matter of perspective. Citation indexing goes beyond the function of categorizing the literature. It explicitly reveals the intellectual relationships that exist between old and new literature. Each article is a published record of a particular event in the process of scientific development. The citation index shows the relationships between individual events at different points in time. That makes a citation index particularly effective in telling us what has happened to some idea or experiment-whether it has been confirmed, extended, improved, tried, or corrected. The third characteristic stems from the second. The citation index focuses our attention on the relationships between scientific events. These relationships can, and frequently do identify the otherwise hidden linkages between events that make up what we call disciplines and specialties. Thus citation indexing inherently classifies the literature it covers. The two characteristics of perspective, plus the semantically different and often