Modeling Issues

Differences between traditional data modeling and time-based data modeling:

• Data Flow
• Timing
• Temporal Composition
• Synchronization

Support for a BLOB (Binary Large Object) data type has been added to most commercial database systems. Although a BLOB does allow the user to reference large data objects, a BLOB does not provide enough support for complex data types.

Key Problem: The description of the structure of time-based media in a form appropriate for querying, updating, and presentation.

• Interpretation
  Traditional data modeling does not consider the interpretation of the data; mainly because the data is of a simple type.

  • Heterogeneity
    • Different media types may be contained within a single storage unit.
  • Interleaving
    • Elements of different media types may be interleaved in a single storage unit.
  • Padding
    • Unused (or blank) data may be added to account for differences in transfer rates.
  • Out-of-order Elements
    • Key elements may be placed ahead of elements that precede it in time.
  • Scalability
    • Only the necessary parts of the data need to be sent to the client. Example, scaling the video stream to a lower resolution before sending it.

  Quality Factors

  • The encoding scheme used determines the quality of the stored information. Some encoding schemes, such as JPEG and MPEG, are lossy.
  • The low level parameters should not be viewable due to the specific nature of the parameters. Only generic quality factors should be viewable.

  Timing

  • There are two timing issues: real-time constraints (display or playback rates) and temporal correlations (relationships between media objects).
  • Real-time constraints are concerned with the sampling rates of record and playback.
  • Temporal correlations are concerned with the timing between media objects, such as synchronization.

  Derivation

  • Derivation is the construction of a media object from another (possible more than one) media object. All that is needed to construct the derived object is the non-derived objects and various parameters needed in the transformation.
  • An example is a "wipe" video transition where one video scene is wiped away to reveal the following scene. The "wipe" video transition can be constructed from the first and second video sequences.
  • The derived object may or may not be stored in the database depending upon the available space and the resources required to construct the derived object.

  Composition

  • Composition refers to the ability to combine two or more "simpler" media types to construct a more complicated media object. This is usually in the form of spatial or temporal relationships.