@article{Bj_rklund_2011,
    doi = {10.1016/j.jcss.2010.04.005},
    url = {https://doi.org/10.1016%2Fj.jcss.2010.04.005},
    year = {2011},
    month = {may},
    publisher = {Elsevier {BV}},
    volume = {77},
    number = {3},
    pages = {450--472},
    author = {Henrik Björklund and Wim Martens and Thomas Schwentick},
    title = {Conjunctive query containment over trees},
    journal = {Journal of Computer and System Sciences}
}

@article{Bj_rklund_2011, doi = {10.1016/j.jcss.2010.04.005}, url = {https://doi.org/10.1016%2Fj.jcss.2010.04.005}, year = {2011}, month = {may}, publisher = {Elsevier {BV}}, volume = {77}, number = {3}, pages = {450--472}, author = {Henrik Björklund and Wim Martens and Thomas Schwentick}, title = {Conjunctive query containment over trees}, journal = {Journal of Computer and System Sciences} }