st.dispose();
st = connection.prepare("create table vertex (db_id INTEGER PRIMARY KEY, id VARCHAR, db_id_inner_graph INTEGER);",false);
st.stepThrough();
st.dispose();
st = connection.prepare("create table edge (db_id INTEGER PRIMARY KEY, id VARCHAR, db_id_source INT, db_id_target INT);",false);
st.stepThrough();
st.dispose();
st = connection.prepare("create table attribute (db_id INTEGER PRIMARY KEY, name VARCHAR, value VARCHAR, value_type VARCHAR);",false);
st.stepThrough();
st.dispose();
st = connection.prepare("create table subgraph (db_id INTEGER PRIMARY KEY, id VARCHAR, name VARCHAR, directed BOOLEAN);",false);