@inproceedings{ten_Cate_2009,
    doi = {10.1145/1514894.1514903},
    url = {https://doi.org/10.1145%2F1514894.1514903},
    year = {2009},
    month = {mar},
    publisher = {{ACM}},
    author = {Balder ten Cate and Phokion G. Kolaitis},
    title = {Structural characterizations of schema-mapping languages},
    booktitle = {Proceedings of the 12th International Conference on Database Theory}
}

@inproceedings{ten_Cate_2009, doi = {10.1145/1514894.1514903}, url = {https://doi.org/10.1145%2F1514894.1514903}, year = {2009}, month = {mar}, publisher = {{ACM}}, author = {Balder ten Cate and Phokion G. Kolaitis}, title = {Structural characterizations of schema-mapping languages}, booktitle = {Proceedings of the 12th International Conference on Database Theory} }