@inproceedings{BeierleBoettcher89,
   AUTHOR = "C. Beierle and S. B{\"{o}}ttcher",
    TITLE = "{PROTOS-L}: {T}owards a Knowledge Base Programming Language",
    BOOKTITLE = "Proceedings GI-Kongre{\ss} Wissensbasierte Systeme",
    YEAR = 1989,
    EDITOR = "W. Brauer and C. Freksa",
    PUBLISHER = {Springer-Verlag}    }