|Getting Started with eHRAF|
The Outline of Cultural Materials (OCM) is an ethnographic subject classification system. The OCM is used to index the eHRAF World Cultures and eHRAF Archaeology databases.
The Outline of Cultural Materials or OCM was first developed by G.P. Murdock and colleagues in the 1930s as an ethnographic subject classification system of social and cultural life. The OCM serves two primary purposes: first, to assist scholars in classifying and annotating cultural materials for all societies; and, second, to aid researchers in readily locating material pertinent to their interests.
The OCM can be used to organize and index a wide variety of databases and collections. At HRAF, the OCM is used to index the eHRAF World Cultures and eHRAF Archaeology databases. In the past, the OCM was used to index the paper and microfiche versions of the HRAF Collection of Ethnography. Every paragraph in every document in eHRAF is indexed with OCM subject categories.
The OCM is now maintained in digital format in an information retrieval thesaurus structure. As such, in addition to being a classifying system, it is also a terminology cross-referencing system. The OCM Index matches a researcher's or an author's terms for a subject with the OCM categories used to index the concept. Additionally, the thesaurus structure adds flexibility and power by making use of hierarchical organization of categories, cross-hierarchy associative relationships, and Boolean query constructs. Work is currently ongoing to make the OCM conform to the ISO 25964 international standard for thesauri.
Because of the terminology cross-referencing aspect of the OCM, it is not necessary for researchers to have a deep knowledge of the OCM subject categories or of the OCM identifiers, formerly called OCM codes. Now, using various thesaurus tools, the researcher can find the appropriate OCM subject category by using his or her own vocabulary terms for the subject. For instance, a researcher interested in finding material related to tattoos can find the word tattoo in the OCM A-Z Index to learn that the correct category to use for material related to tattoos is identified by the term BODY ALTERATIONS, which has an OCM identifier of 304. You can see how this works in eHRAF by going to Browse Subjects by A-Z Index. It is even possible to let the programmatic system automatically look up the correct category and perform a search. To see how this works in eHRAF, go to Basic Search.
While not necessary, it is still valuable to have significant knowledge of the OCM subject categories and of the OCM structure. For instance, when the built in terminology cross referencing is not sufficient for particular search purposes, it might work best to customize a search by choosing subjects based on understanding the category scope notes. The OCM can also serve as a valuable outline to study the topic of ethnographic subjects. Finally, it is useful to know the OCM identifiers to use as shorthand for the OCM categories.
The hierarchical thesaurus organization of the OCM allows researchers to more easily customize their searches to either broaden a search, thus maximizing recall, or to narrow a search, thus maximizing precision. If you choose categories higher up in the hierarchy and all the descendants of the category, all of the sibling children, and all of the children's children will also be included in the search, thus increasing recall. If you choose categories further down in the hierarchy and only those chosen narrower categories and their descendants, if any, will be included in the search, thus increasing precision. In eHRAF, the OCM hierarchy can also be browsed beginning at the top level of its Major Subjects, or by the traditional OCM identifier order.
In eHRAF, you can examine the details of an OCM subject category in the Subject Profile or in pop-up windows available by clicking on an OCM identifier wherever an OCM category is referenced in Search Results or Advanced Search.