摘要：On-line circulation systems divide into two typ es . One type contains r ec ord s only for charged or otherwise absent it e ms. Th e other contains a file of records for all titles or volumes in the library collection, regardle ss of th e ir circulation status. This pap e r trac e s differenc es between the two types, examining different kinds of files and t e rminals , transaction evidence, the quality of bibliographic data , qu e rying, and th e possibility of functions outside circulation. Aspects of both operational and potential syst e ms are considered.
