Mention the number of authors of the paper 'PerfectDoc: A Ground Truthing Environment for Complex Documents'.
How many authors does the publication 'PerfectDoc: A Ground Truthing Environment for Complex Documents' have?
SELECT ?answer WHERE { <https://dblp.org/rec/conf/icdar/YacoubSS05> <https://dblp.org/rdf/schema#numberOfCreators> ?answer }
<https://dblp.org/rec/conf/icdar/YacoubSS05>