Which vertical search engines are relevant?

@inproceedings{zhou-2013-vertical, author = {Ke Zhou and Ronan Cummins and Mounia Lalmas and Joemon M. Jose}, editor = {Daniel Schwabe and Virg\'{i}lio A. F. Almeida and Hartmut Glaser and Ricardo Baeza-Yates and Sue B. Moon}, title = {{Which vertical search engines are relevant?}}, booktitle = {{22nd International World Wide Web Conference, WWW '13, Rio de Janeiro, Brazil, May 13-17, 2013}}, pages = {1557--1568}, publisher = {International World Wide Web Conferences Steering Committee / ACM}, year = {2013}, url = {https://doi.org/10.1145/2488388.2488524}, doi = {https://doi.org/10.1145/2488388.2488524} }