protected Table getMainTable() {
if (mainTable == null) {
Table mt = getSchema().newTable("MAIN");
Column mtId = mt.newColumn("ID", Column.Type.BIGINT);
Column mtVer = mt.newColumn("VER", Column.Type.INTEGER);
StringColumn mtName = (StringColumn) mt.newColumn("NAME", Column.Type.VARCHAR);
mtName.setLength(60);
BinaryColumn mtSig = (BinaryColumn) mt.newColumn("SIG", Column.Type.BINARY);
mtSig.setLength(16);
mt.newColumn("DATE", Column.Type.DATE);