@article{Gottlob_2001,
    doi = {10.1145/382780.382783},
    url = {https://doi.org/10.1145%2F382780.382783},
    year = {2001},
    month = {may},
    publisher = {Association for Computing Machinery ({ACM})},
    volume = {48},
    number = {3},
    pages = {431--498},
    author = {Georg Gottlob and Nicola Leone and Francesco Scarcello},
    title = {The complexity of acyclic conjunctive queries},
    journal = {Journal of the {ACM}}
}

@article{Gottlob_2001, doi = {10.1145/382780.382783}, url = {https://doi.org/10.1145%2F382780.382783}, year = {2001}, month = {may}, publisher = {Association for Computing Machinery ({ACM})}, volume = {48}, number = {3}, pages = {431--498}, author = {Georg Gottlob and Nicola Leone and Francesco Scarcello}, title = {The complexity of acyclic conjunctive queries}, journal = {Journal of the {ACM}} }