Librarians have experienced numerous changes in technical processes and information retrieval in recent years. The most significant changes relate in some degree to the computerization of library functions. Many librarians have seen the change from the older Library of Congress card order slips to the newer optical scan slips and eventually to computer produced cards. Academic libraries, for the most part, were among the strongest advocates of the new technologies. In many instances, academic libraries with their access to institutional computer facilities developed in-house programs to perform routine functions. However, without any suitable guidelines for standardized formatting, these in-house systems often were less than desirable for a number of reasons – poor planning, shortsightedness, computer limitations, etc. Once the library community and those responsible for funding library operations realized that the use of computers and computer systems by librarians was inevitable, the next logical step was to design or select programs which would serve both the institution and the library community. The gradual computerization of the union list illustrated this trend. The first significant effort with union listing did not occur until the first edition of the Union List of Serials in 1927. While both the first edition of the Union List of Serials and the subsequent second and third editions were monumental bibliographic projects, there was one persistent problem – even with supplements, printed lists quickly became outdated. Keeping track of new titles, cessations, cancellations, etc., is of major importance if accuracy in institutional 98holdings is to be maintained. The problem of up-to-dateness can now be resolved thanks to online computer technology and union listing options available through the OCLC Serials Control Subsystem. The union listing component, as described below, is an integral part of the serials subsystem. The local data record provides the basis for union listing:

The Union List is designed to be copy specific. There must be a separate local data record for each copy of a title held. The OCLC system merges these local data records together to form a single union list display. The merging process is determined by the union list group or groups for which a library has been profiled. What this means it that, in addition to an individual institution’s profile, participating libraries are given a common symbol under which their individual symbols are merged. All current OCLC libraries in Pennsylvania are profiled under the symbol PASU. If, for example, the Falk Medical Library joined a medical libraries union list group under the symbol MLUL, its holdings for a particular title would be retrieved by union list searches for either PASU or MLUL. In the OCLC Union List Display, the local data record does not stand alone. It is tied to a full serial bibliographic record. (Sperry 2)