21-04-2011, 12:17 PM
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1. Introduction
• A multimedia database management system (MMDBMS) is a framework that manages different types of data potentially represented in a wide diversity of formats on a wide array of media sources.
• The multimedia DBMS provides support for multimedia data types, plus facilities for the creation, storage, access, query and control of the multimedia database.
2. Purpose of Multimedia Data Base Management System
A Multimedia database management system provides a suitable environment for using and managing multimedia database information.
It must support the various multimedia data types , in addition to providing facilities for traditional DBMS functions like database definition and creation, and retrieval, data access and organization, data independence, privacy, integration, integrity control, version control and concurrency support.
Using the general functions provided by a traditional DBMS as a guide, we can describe the purposes of a multimedia DBMS as follow
Integration : Ensures that data items needs not be duplicated during different program invocation requiring the data.
Data Independence: Separation of the database and the management functions from the application programs.
Concurrency Control: Ensures multimedia database consistency through rules, which usually impose some form of execution order on concurrent transactions.
Persistence: The ability of data objects to persists (survive) through different transactions and program invocations.
Privacy: Restrict unauthorized access and modification of stored data.
Integrity control: Ensures consistency of the database state from one transaction to another through constraints imposed on transaction.
Recovery: Methods needed to ensure that results of transaction that fail do not affect the persistent data storage.
Query Support: Ensure that that the query mechanisms are suited for multimedia data.
Version Control: Organization and management of different version of persistent objects, which might be required by applications.
In concurrency control, a transaction is a sequence of instructions executed either completely or not at all. In the latter case, the database is restored to its previous state. Defining the appropriate granularity for concurrency is a problem in multimedia database. Traditional database use a single record or table as the unit of concurrency. Multimedia databases typically use a single object as the logical unit of access. Thus the single multimedia object could form the unit of concurrency.
In achieving persistence, a simple method is to store the multimedia files in some operating system files. However, the huge data volumes make this approach costly to implement. Moreover the system also needs to store the multimedia metadata and possibly composite multimedia objects. Thus most multimedia DBMS classify the data as either persistent or transient and store only persistent data after transaction updates. Persistent data after transaction updates transient data are used only during program or transaction execution and are removed afterwards.
Traditionally, a query selects a subset to the data objects of the data object based on the user’s description of what data to access. A query usually involves various attributes. Possibly keyword-based or Content oriented and is usually interactive. Thus functions for relevance feedback and query formulation. Similarity matches and mechanisms for displaying ranked results are important in multimedia DBMS
Version control becomes important when a persistent multimedia object is updated or modified as some application might need to access previous states of the object. A DBMS provides such access through versions of the persistent objects. For a multimedia DBMS the huge volumes of data reinforces the importance of efficiently organizing such versions. Moreover the available storage might limit the provision of version in addition, version management may involve not only version of single objects but also versions of the complex objects that make up the multimedia database.
The special nature of multimedia data also makes it important to support new special functions. These include object composition and decomposition, management of huge volumes of multimedia data, effective storage management and information retrieval and handling of spatial and temporal data objects
3. Requirements for the multimedia DBMS
For multimedia DBMS to serve its expected purpose, it must meet certain special requirements.
Traditional DBMS capabilities
Huge capacity storage management
Information retrieval capabilities
Media Integration, Composition and presentation
Multimedia Query support
Multimedia interface and interactivity
Performance
4. Multimedia Objects: Characteristics
• Multimedia databases can be accessed by queries on any of the objects composing the databases.
• The properties of these media objects distinguish the needs of a multimedia database management system from those of a traditional one as below:
(a) Text Data
• Text data is often represented as strings. However, text as used in multimedia document systems, includes structural information such as title, author etc.
• Hence one needs a language environment to reflect the structural composition of the text data.
• Standard Generalized Markup Language (SGML) is a document representation language defined by International Standards Organization (ISO).
• Another environment named the Hypermedia/Time-based Structuring Language (Hytime) has also been defined to include support for hypermedia documents (hypertext with multimedia objects), with links and support for inclusion of multimedia objects in a text document specifications.
• SGML together with HyTime can be used for developing multimedia document.
(b) Audio Data
• Audio data has an inherent time dependency associated with it. The time scale associated with audio objects has to be uniform for a meaningful interpretation.
• Audio has to be digitized before it can be processed. Size of digitized audio depends on the technique used, which in turn depends on the desired audio quality.
• For instance, a normal voice quality digitization is done at 8 kHz with 8 bits per sample, and hence it produces 64Kb/s of data.
• CD quality digitization is carried out at 44.1 KHz sampling rate with 16 bits per sample and hence produces 1.4Mb/s. Digitized audio can be effectively compressed to reduce storage requirements.
© Image Data
• Image data represents digitized drawings, paintings, or photographs. The size of a digitized image depends on the required quality.
• Color images and photographs require more storage space. Typically, a color image or a photograph needs the RGB components of each pixel to be stored.
• Depending on the color scale chosen, one might need 8 bits per color component implying 24 bits per pixel.
• Hence 1024*1024 pixel image, a storage space of 24 Mbits is needed.
• Compression schemes are used to reduce the volume of data that needs to be stored.
• Different compression algorithms as well as storage representations can be employed and this results in different formats of digitized images and photographs.
• Joint Photographers Encoding Group (JPEG) is one such format for images, which has been standardized by ISO.
• Other popular formats include Graphic Interchange Format (GIF) and Tag Image Format (TIFF).
(d) Video Data
• Video data represents the time dependent sequencing of digitized pictures or images called video frames.
• The number of video frames for one second depends on the standard that is employed.
• NTSC (National Television System Committee) standard employs 30 frames/second while PAL (Phase Alternation Line) employs 25 frames/second.
• Further, the pixel size of a frame depends on the desired quality. Normal NTSC frames are 512 * 480 pixels in size, HDTV (High Definition Television) frames employ 1024 * 1024 pixels.
• The number of bits needed per pixel reflects the quality of digitized video frame. Digitized video requires large storage space. Compression schemes need to be employed to reduce the volume of data to be stored.
• Motion Picture Encoding Group (MPEG) is a standard that has been specified by the ISO for compression and storage of video. The standard MPEG 2 specifies the methodology for storing audio along with compressed video.
4.1 Access Dimensions of the Media Objects
• With reference to the process of accessing the contents, media objects can be considered as one of the following:
(a) 1-Dimensional Objects
Text and audio have to be accessed in a contiguous manner (as ASCII strings or signal waves). Hence, text and speech can be considered as 1-dimensional objects.
(b) 2-Dimensional Objects
Access to image data can be done with reference to the spatial locations of objects. For example, a query can search for an object that is to the right of or below a specified object. So image objects can be considered as 2-dimensional since it has a spatial content.
© 3-Dimensional Objects
Video has spatial characteristics as well as temporal characteristics. Access to video can be done by describing the temporal as well as the spatial content. For example, a query can ask for a movie to be shown from 10 minutes after its starting point. Hence, video can be considered as a 3-dimensional object.
• The access dimension of an object, in a way, describes the complexity in the process of searching. For 1-dimensional objects, such as text and audio, the access is limited to the keywords that appear as part of text or speech.
• For image, the access is done by specifying the contents as well as their spatial organization. In a similar manner, access to video should comprise of the sequencing of video frames in the time domain.
