Subject access points (SAPs) / Search keys / Entry points

Traditional subject access points are index terms and classifications explicitly designed for subject searching. After the electronic revolution should subject access points, however, be understood in a much broader way. Already in the 1950s it became common to make experiments comparing the utility of different kinds of access points in bibliographical databases (e.g. titles, abstracts, descriptors, classification symbols). Later followed experiments with references (in citation indexes) and words in full-text-databases as access points. Almost any element in a bibliographical record, including all full texts elements and all kinds of value added information has become potential SAPs. This is the way this concept is understood by Hjørland & Kyllesbech Nielsen (2001). Among the providers of SAPs are:

Research about how different SAPs contributed to recall and precision showed that different kinds of SAPs supplement each other. While it is possible to formulate very general heuristic rules, the optimal search strategy in single case depends on a creative combination of SAPs made for the specific question at hand. An example of a heuristic rule is: start by searching descriptors. If the search set is too small increase with titles, abstracts, identifiers and full-text (in that order). If a search set is too large and with too much noise demand that the search term is in both title and descriptor. If still too large limit the search to core scientific journals in the field (based on, for example, Bradfordization or impact factor). Such heuristic rules serve some purposes. However, it is easy to produce examples, in which these heuristic rules are not valid, why IR should always aim at a creative search based on knowledge about specific literatures and databases.


Rowley & Farrow (2000, p. 245) uses the term SAP in a much narrower sense. They find (p. 253) that “the concept of the access point belongs to manually searched indexes, and is arguable irrelevant to databases with search systems allowing keyword access”. As it is understood by Hjørland & Kyllesbech Nielsen (2001) it is fundamental to every kind of information retrieval and is a fundamental concept that is not obsolete.


Hjørland & Kyllesbech Nielsen (2001, p. 260) provided the following taxonomy of SAPs:



A basic thesis in Hjørland & Kyllesbech Nielsen (2001) is that a given subject access point, say a title word does not have a given or constant value for information retrieval. Titles vary from context to context and thus the precision and values of titles for information retrieval. The same is true to any kind of SAP. A theory of how best to utilize SAPs must therefore consider how they are designed in different domains. The value of any SAP is relative both in relation to the domain and to other SAPs. This insight makes text composition studies and genre studies relevant for IR. How documents are designed in different genres provide some objective possibilities for what may be used as SAPs (if the system makes them searchable and if searchers are able to utilize them). From this point of view is traditional research in IR merely a study of statistical averages that do not take genre variations in texts into account.


A distinction is made between subjective search possibilities on the one hand and objective search possibilities on the other hand. The objective possibilities mean that you cannot find something, that is not there. If a database does not provide opportunities to search, for example, bibliographical references (as in citation indexing) then you cannot use references as subject access points, this search possibility simply does not exist (objectively). If, on the other hand, somebody does not know what a citation index is, and cannot utilize it, then the subjective search possibilities are not present. 


"The subject index, even after the decline discussed above, is still one of the most commonly used search access points in the online catalog. It is also, unfortunately, the access point most likely to fail, often providing either no items that match the user’s search request, or too many items to evaluate conveniently"  (Larson, 1991, p. 207).


"This suggests that the improvement in search success is related to the decrease in the use of the subject index". (Larson, 1991, p. 208).


"This study has shown that a constant decline has taken place in the use of the subject index in a large online catalog. Title keyword searching, which provides a limited form of natural-language access to the topics of books, was found to be the primary replacement for subject index use. The causes and implications were explored and evidence provided suggesting that user frustration

in using the subject index effectively has led to this decline. The two major problems contributing to user frustration are search failure, due to difficulties in dealing with LCSH, and information overload, due to the ever-increasing size of the database." (Larson, 1991, p. 213-214).






Hjørland, B. & Kyllesbech Nielsen, L. (2001). Subject Access Points in Electronic Retrieval. Annual Review of Information Science and technology, 35, 249-298. Click for full-text .pdf (3,6 MB). Kommenteret parafrase (In Danish) by Dorte Nielsen, 2002: Parafrase.doc


Larson, R. R. (1991). The Decline of Subject Searching: Long-Term Trends and Patterns of Index Use in an Online Catalog. Journal of the American Society for Information Science, 42(3), 197-215.


Pirkola, A. & Järvelin, K. (2001). Employing the resolution power of search keys. Journal of the American Society for Information Science and Technology, 52(7), 575-583.


Reid, J.; Lalmas, M.; Finesilver, K. & Hertzum, M. (2006). Best entry points for structured document retrieval—Part I: Characteristics. Information Processing & Management, 42(1), 74-88.


Rowley, J. & Farrow, J. (2000). Organizing Knowledge: An Introduction to Managing Access to Information 3rd. Edition. Hampshire, England: Gower Publishing Limited.


Wyly, B. J. (1996). From access points to materials: A transaction log analysis of access point-value for online catalog users. Library Resources & Technical Services, 40(3), 211-236.



See also: Search term (Core Concepts in LIS);




Birger Hjørland

Last edited: 17-04-2007






  1. Subject access points reflect organized knowledge from the users' perspective: What possibilities are available to searchers (whether or not they understand how to utilize them in optimal ways). Why and how should people involved in indexing and classification documents (whether "manual" or "automated") learn about them?