Get all distinct predicates from a single ontology

Database: 
Statement: 

Get all distinct predicates from a single ontology </br> A limit of results per page $number$ (e.g., 10)

Query: 
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> SELECT DISTINCT ?predicates WHERE { GRAPH <http://bioportal.bioontology.org/ontologies/BHO> { ?s ?predicates ?o . } } limit ??number