@article{DBLP:tr/ibm/IWBS150,
author = {Thomas Ludwig and
Bernd Walter},
title = {EFTA: A Database Retrieval Algebra for Feature Terms},
journal = {IWBS Report},
publisher = {IBM Germany Science Center, Institute for Knowledge Based
Systems},
volume = {150},
year = {1991},
bibsource = {DBLP, http://dblp.uni-trier.de}
}