Frits L. Engel J. J. Andriessen H. J. R. Schmitz What, Where and Whence: Means for Improving Electronic Data Access. 145-160 1983 18 International Journal of Man-Machine Studies 2 db/journals/ijmms/ijmms18.html#EngelAS83 http://dx.doi.org/10.1016/S0020-7373(83)80027-3