CREATE TABLE conference (cid NUMBER, homepage VARCHAR2, name VARCHAR2)
CREATE TABLE writes (aid NUMBER, pid NUMBER)
CREATE TABLE cite (cited NUMBER, citing NUMBER)
CREATE TABLE domain_publication (did NUMBER, pid NUMBER)
CREATE TABLE publication_keyword (kid NUMBER, pid NUMBER)
CREATE TABLE organization (continent VARCHAR2, homepage VARCHAR2, name VARCHAR2, oid NUMBER)
CREATE TABLE publication (abstract VARCHAR2, cid NUMBER, citation_num NUMBER, jid NUMBER, pid NUMBER, reference_num NUMBER, title VARCHAR2, year NUMBER)
CREATE TABLE domain_journal (did NUMBER, jid NUMBER)
CREATE TABLE journal (homepage VARCHAR2, jid NUMBER, name VARCHAR2)
CREATE TABLE keyword (keyword VARCHAR2, kid NUMBER)
CREATE TABLE domain_author (aid NUMBER, did NUMBER)
CREATE TABLE domain (did NUMBER, name VARCHAR2)
CREATE TABLE domain_conference (cid NUMBER, did NUMBER)
CREATE TABLE domain_keyword (did NUMBER, kid NUMBER)
CREATE TABLE author (aid NUMBER, homepage VARCHAR2, name VARCHAR2, oid NUMBER)

return me the references of ' Making database systems usable ' .
SELECT reference_num FROM publication WHERE title = 'Making database systems usable'
SELECT "reference_num" FROM "publication" WHERE "title" = 'Making database systems usable'