@article{DBLP:tr/ibm/IWBS89,
  author    = {Christoph Beierle and
               Stefan B{\"o}ttcher},
  title     = {PROTOS-L: Towards a Knowledge Base Programming Language},
  journal   = {IWBS Report},
  publisher = {IBM Germany Science Center, Institute for Knowledge Based
               Systems},
  volume    = {89},
  year      = {1989},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}