It is critical for applications to obtain enough quality of service (QoS) from multimedia objects. Not only states but also QoS of objects are changed by performing the methods on the objects. The objects are required to be consistent in presence of multiple transactions. We discuss new types of equivalent and conflicting relations among methods with respect to QoS. We also introduce two types of locking modes, serialization and mutual exclusion modes to synchronize concurrent accesses to objects based on the QoS relations.