lib/api.js
function(identifier, target, cb) {
    logger.info('get head system: ' + identifier);
    var systemId = _sr.findSystem(identifier);
    if (!systemId) { logger.error(ERR_NOSYSID); return cb(new Error(ERR_NOSYSID)); }
    _sr.getHead(systemId, target, cb);
  }
function(identifier, target, cb) {
    logger.info('get head system: ' + identifier);
    var systemId = _sr.findSystem(identifier);
    if (!systemId) { logger.error(ERR_NOSYSID); return cb(new Error(ERR_NOSYSID)); }
    _sr.getHead(systemId, target, cb);
  }
get the full head system definition (latest revision)