return me the number of authors of " Making database systems usable " .
SELECT COUNT ( DISTINCT t1.name ) FROM writes AS t2 JOIN author AS t1 ON t2.aid  =  t1.aid JOIN publication AS t3 ON t2.pid  =  t3.pid WHERE t3.title  =  "Making database systems usable";
SELECT COUNT ( DISTINCT t1.name ) FROM writes AS t2 JOIN author AS t1 ON t2.aid  =  t1.aid JOIN publication AS t3 ON t2.pid  =  t3.pid WHERE t3.title  =  "Making database systems usable";
[{'COUNT ( DISTINCT t1.name )': 0}]