Virtual OPACs versus union database: two models of union catalogue provision

Z39.50 is often put forward as a means of providing a virtual union catalog ue without the need for a physical union database. This paper considers som e of the major technical and organisational issues involved in virtual cata logue production, contrasting them with the traditional union catalogue app roach exemplified by COPAC. A way of integrating these two models of the un ion catalogue is suggested, which would allow effective service provision i n the immediate future.