Abstractions for Multimedia Database Systems - CiteSeerX

Proc. 2nd Int. Workshop on Multimedia Information Systems, Sept. 26-28, 1996. West Point, New York, USA.

Abstractions for Multimedia Database Systems Thomas C. Rakow, Wolfgang Klas,and Erich J. Neuhold GMD - Integrated Publication and Information Systems Institute (IPSI) Address: Dolivostrae 15, D-64293 Darmstadt, Germany WWW: http://www.darmstadt.gmd.de/~frakow, klas, neuholdg E-Mail: frakow, klas, [email protected]

Abstract In this article we point out important functionality needed to support advanced multimedia applications by a database management system. We introduce a generic datatype to support the implementation of time-dependent media like audio, video, and animation. Besides the demand for speci c multimedia datatypes we sketch a taxonomy for the modeling of meta information. Multimedia presentations are made independent from formats and devices similar as data are made independent from physical storage. The developments achieved so far with the AMOS prototype currently under implementation at our institute illustrates the chosen architecture of a multimedia database management system. 

New Address: Department DBIS, University of Ulm, D-89069 Ulm, e-mail: [email protected]

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1 Introduction In advanced multimedia applications, the user accesses the system via a hypermedia authoring and reading environment, e.g. via WWW tools. Multimedia information among images, audio, and video includes animations, i.e. graphics generated in real time during presentation. Hence, modeling concepts for time-dependency and for synchronized presentation of multimedia data as well as time-constrained delivery of multimedia data to presentation clients must be available by a multimedia DBMS (MM-DBMS). Recent developments for video-on-demand systems support to a high degree time-continuous presentation of a single media type1 but neglect editing, capture, and especially modeling of single media as well as multimedia compositions required in advanced multimedia applications. Although it is frequently said that in a client/server environment modeling of data is part of the client's business and no speci c modeling is needed of the DBMS server, ef cient multimedia support requires modeling of media-speci c characteristics at the server. For example, a time-dependent MPEG audio and video stream requires for editing as well as for adaptation purposes a reference lists to I-, P-, and B-frames as well as to the audio sequences. Unfortunately, it seems that most vendors do not plan to consider such support of time-dependent data types in the future. In the standardization eort SQL-3/MM only methods for text retrieval, spatial data, and complex numbers are discussed [ISO95]. As current DBMSs oer inadequate abstractions for advanced multimedia applications, we are developing a number of features of what we consider to be some of the most prominent constituents of a MM-DBMS needed for adequate application support: a datatype continuous Video in such systems can be designated as single media because audio cannot be accessed independently from video. 1

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long elds, object-oriented modeling of multimedia metadata, and presentation independence.

These concepts are utilized by the means of a client/server architecture that supports a heterogeneous and distributed environment. However, we do not claim to have found a solution for all the many features and properties required by a MM-DBMS. For example, we do not address content-based retrieval for audio and video data and indexing for such data. In the following, we describe the topics we focus on and the results we have achieved so far.

2 Continuous Long Fields From the application programmer's view, a data structure for representation and storage of time-dependent data is similar to a long eld (binary large object, BLOB) but access is encapsulated by means of seconds of presentation time rather than by byte numbers. Speci cations of quality of service parameters (to support continuous data delivery) and of adaptation schemes (e.g. changing resolution) have to be provided by the application programmer. We have developed a strategy for loading and replacement of continuous objects called Least/Most Relevant for Presentation (L/MRP) [MKK95]. The strategy supports user interactions like changing direction of playout or speed or jumping to a prede ned temporal point. Despite speci c buer strategies, there is no guarantee of continuity for time-dependent data streams at times of high system load. Techniques become even more complicated when synchronized presentations of several media streams contain time-dependent as well as discrete data and when user interactions like changing direction or speed have to be supported. We have developed a so called smooth adaptation technique that supports overlapping intervals for the change of media quality and restrictions for frame dropping [HKR96]. 3

3 Modeling of Object-Oriented Metadata We make usage of object-oriented modeling approach as a very promising basis for the multitude of multimedia data types and their manipulation needs. Besides, content-based retrieval of multimedia data depends on the availability of rich metadata or meta-knowledge about the original multimedia data. The metadata can be based on knowledge incorporating the semantics of the data and the intended usage in a particular application. Or it might be (semi-) automatically derived from the original data by employing speci c analysing techniques. Metadata can be classi ed according to the following taxonomy [BR94]: Metadata for the representation of media types (e.g. format, coding, language), content-description, content classi cation (e.g. level of expertise), document composition (e.g. title, de nition), document history (e.g. status of approval), document location (e.g. an uniform resource locator (URL) in the web), and document collections (e.g. number of documents written by a certain author).

4 Presentation Independence Current DBMSs do not oer support for continuous data transport to and presentation at the user's workstations. We claim, that an MM-DBMS should provide presentation independence as it provides data independence. Then, application programs are relieved from

speci c data codings as well as time-dependencies in presentations. We call the service supporting presentation independence at the client playout management [BKL96, TK96]. It oers synchronized presentation of user-modeled compositions of discrete as well as continuous data. In addition, it supports user interaction to control the presentation (start, stop, 4

etc.), provides for user-initiated selection of presentation parts (e.g., branching), and allows for application-speci c input (e.g., color and speed of a car shown in the presentation). A playout management service can guarantee a certain presentation quality. However, such a service must also operate in non-realtime environments in which best eort service strategies have to be performed instead.

5 Architecture of a MM-DBMS In a client/server environment data objects can be partitioned between server and client [RNL95]. We decided for ease of implementation and for re-implementation on other platforms to use a client environment with built-in data types. Hence, persistent objects are created only at the server. This restriction prevents con icts and inconsistencies produced by uncoordinated changes in local replicas of media objects. In addition, it may be impossible to copy complete multimedia objects to the clients due to their limited storage capacity. As a consequence invocations of manipulation methods are always sent to the server for execution. Changes become visible to concurrent users of the database immediately after the completion of a transaction. The rst prototype of a MM-DBMS called AMOS developed at our institute implements this architecture and oers the concepts as introduced in this article [Rak96].

References [BKL96] S. Boll, W. Klas, and M. Lohr. Integrated Database Services for Multimedia Presentations. In S. M. Chung, editor, Multimedia Information Storage and Management. Kluwer Academic Publishers, 1996.

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[BR94] [HKR96] [ISO95] [MKK95] [Rak96] [RNL95]

[TK96]

K. Bohm and T.C. Rakow. Metadata for Multimedia Documents. SIGMOD Record (Special Issue on Meta-data for Digital Media), 23(4):21{26, December 1994. S. Hollfelder, A. Kraiss, and T. C. Rakow. A Buer-Triggered Smooth Adaptation Technique for Time-Dependent Media. Number 1002 in Technical Report (Arbeitspapiere der GMD). GMD Sankt Augustin, June 1996. ISO/IEC JTC1/SC21/WG3. ISO Working Draft SQL Multimedia and Application Packages (SQL/MM), September 1995. F. Moser, A. Krai, and W. Klas. L/MRP: A Buer Management Strategy for Interactive Continuous Data Flows in a Multimedia DBMS. In Proc. Int. Conf. of Very Large Data Bases 1995 (VLDB), pages 275{286, Sep. 1995. T.C. Rakow. Active Media Object Stores (AMOS). http://este.darmstadt.gmd.de:5000/dimsys/amos/home.html, 1996. T.C. Rakow, E.J. Neuhold, and M. Lohr. Multimedia Database Systems - The Notions and the Issues. In G. Lausen, editor, Tagungsband GI-Fachtagung Datenbanksysteme in Buro, Technik und Wissenschaft (BTW), Informatik Aktuell, pages 1{29. Springer, March 1995. H. Thimm and W. Klas. Delta-Sets for Optimized Reactive Adaptive Playout Management. In Proc. 12th Int. Conf. on Data Engineering (ICDE), pages 584{ 592, Feb. 1996.

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