rowid. The value in the ROWID_OBJECT column of the record.
systemName and sourceKey. The systemName is the name of the system to which the record belongs. The sourceKey is the value in the PKEY_SRC_OBJECT column of the record.
Global Business Identifier (GBID) of an object. A GBID can be a compound value, in which case you must pass all the values.
The GBID approach works only with the ReadBE service.

String systemName = "SFA";

Properties config = new Properties();
config.put(SiperianClient.SIPERIANCLIENT_PROTOCOL, EjbSiperianClient.PROTOCOL_NAME);
CompositeServiceClient client = CompositeServiceClient.newCompositeServiceClient(config);
CallContext callContext = new CallContext(orsId, user, pass);
helperContext = client.getHelperContext(callContext);
DataFactory dataFactory = helperContext.getDataFactory();

//String personRowId = "1097";
String pkeySrcObject = "CST1379";

//Set custom key pkey
pkey = (Key) dataFactory.create(Key.class);
pkey.setSystemName(systemName);
pkey.setSourceKey(val);
writePerson.setKey(pkey);