In this paper, we presented models for different schemas in a distributed multimedia system, and algorithms to perform the transformation between them. We then described a unified object exchange format (OEF) for composite multimedia objects.
The hypergraph model provides the static structure of multimedia objects with its rich set of hyperlinks, while the G-Net model provides flexibility and power to combine different aspects of the DMS into an integrated system. The G-Net model also enables a user to specify the MDS and MCS at a high level of abstraction. Furthermore, the G-Net is hierarchical, dynamic, and directly executable [4]. The MSS-to-MDS transformation algorithm transforms the high-level specification of MMOs into a data schema that can be used to perform presentation of MMOs. The MDS-to-MCS transformation algorithm transforms the data schema into the corresponding communication schema that supports the transmission of the objects.
The research issues currently under our investigation include the modeling of interaction, ``fuzzy scenarios" [12], and other synchronization scenarios; the feasibility of our model on complex applications; detailed specification and evaluation of the QOS parameters; the degradation model and heuristics for the negotiation with the QOS manager; the adaptability of the transformation algorithms in taking the dynamic feedback from the QOS manager to adjust its behavior in order to optimize the usage of the bandwidth in accordance with the reliability of the network; and the heuristics for optimizing the construction of G-Nets that represent the MDS and MCS.
The design and interaction of the Object Exchange Manager in the distributed multimedia system was also described in this paper. The Object Exchange Manager has the functions of packing all MMO data into OEF and unpacking all data in OEF to construct an active MMO, transferring OEF through network using network primitives provided, and performing relevant operations during packing/unpacking, such as compression/decompression, and encoding/decoding.
Due to its object oriented design, the OEM has the advantages of easy extension as well as information hiding and reusibilty. Besides, after compression and encoding, an MMO could have a reduced size and could be in ASCII form, making the transmission of the MMO scalible and flexible. The OEM is independent of the underlying network. It can either use the Network Management Module in our system or other network service. Currently, our AMS is using TCP/IP as the transport service provider, and Ethernet as the underlying network. As this does not meet the needs of real time presentation of an MMO, we plan to investigate and employ a more suitable network service protocol.
Another research issue is the compatibility of our Object Exchange Format to the existing and forthcoming standards, for examples, ISO standards MHEG and PREMO (Presentation Environment for Multimedia Objects) [10]. Our Object Exchange Format will be revised to adapt to the notations of the standards and the Object Exchange Manager will be enhanced to support classes specified in the standards. Since the standards adopts object-oriented approach, we believe that it will be feasible to integrate our OEM into the object class hierarchy of the standards.