Images, sounds and movies can be stored, retrieved and played by many databases. In future, multimedia databases will bcome a main source of interaction between users and multimedia elements. Multimedia storage and retrieval Multimedia storage is characterized by a number of considerations. They are:
(i) massive storage volumes
(ii) large object sizes
(iii) multiple related objects
(iv) temporal requirements for retrieval
Massive Data Volumes
A single multimedia document may be a combination of different media Hence indexing of documents, fi lms and tapes is more complex. Locating massive data volumes requires searching through massive storage files.
Locating and indexing systems can be understood only by a few key staff personnel. Hence it requires a major organizational eff0l1 to ensure that they are returned in proper sequence to their original storage location.
There are two major mass storage technologies used currently for storage of multimedia documents.
(i) Optical disk storage systems. (ii) High-speed magnetic storage.
Advantages of Optical disk storage systems:
(i) Managing a few optical disk platters in a juke box is much simpler than man;lging a large magnetic disk farm. (ii) Optical disk storage is excellent storage system for off line archival of old and infrequently referenced documents for significant periods of time
Multimedia object storage
Multimedia object storage in an optical medium serves its original purpose, only if it can be located fast and automatically. A key issue here is random keyed Access t6 various components of hypermedia database record. Optical media providcs very dense storage. Speed of retrieval is another consideration.
Retrieval speed is a direct result of the storage latency, size of the data relative to display resolution, transmission media and speed, and decompression efficiency. Indexing is important for fast retrieval of information. Indexing can be at multiple levels.
Multimedia document retrieval
The simplest form of identifying a multimedia document is by storage platter identification and its relative position on the platter (file number). These objects can then be grouped using a database in folders (replicating the concept of paper storage in file folders) or within complex objects representing hypermedia documents.
The capability to access objects using identifiers stored in a database requires capability in the database to perform the required multimedia object directory functions. Another important application for sound and full motion video is the ability to clip parts of it and combine them with another set.
Indexing of sound and full-motion video is the subject of intense debate and a number of approaches have been used.
Database Management Systems for Multimedia Systems
Since most multimedia applications are based primarily on communications technologies, such as electronic mail, the database system must be fully distributed. A number of database storge choices are available.
The choices available are:
* Extending the existing relational database management systems, (RDBMSs) to support the various objects for multimedia as binary objects.
* Extending RDBMSs beyond basis binary objects to the concepts of inheritance and classes. RDBMSs supporting these . features provide extensions for object-programming front ends and/or C++ support.
* Converting to a full fledged object oriented database that supports the standard SQL language.
* Converting the database and the application to an objectoriented database and using an object-oriented language, or an object-enabled SQL for development.
Multimedia applications combine numerical and textual data, graphics from GUI front-ends, CAD/CAM systems and GIS applications, still video, audio and full-motion video with recorded audio and annotated voice components. Relational databases, the dominent database paradigm, have lacked the ability to support multimedia databases. Key limitations of relational database systems for implementing multimedia applications stem from two areas: the relational data model and the relatIonal computational model.
RDBMSs have been designed to manage only tabular alphanumeric forms of data (along with some additional data types stored in binary form such as dates).
RDBMS EXTENSIONS FOR MULTIMEDIA
Binary Large Object (BLOB) is a data type which has been adapted by most of the leading relational databases. BLOBs are used for objects such as images or other binary data types.
The relational database is extended to access these BLOBs to present the user 'with a complete' data set. Extended relational databases provide a gradual migration path to a more object-oriented environment. Relational database tables include location information for the BLOBs which may be stored outside the database on separate image or video servers. Relational databases have the strength of rigorous set management for maintaining the integrity of the database
Object-Oriented Databases for Multimedia
.In object databases, data remains in RMS or flat files. Object databases can provide the fastest route to multimedia support. Object programming embodies the principles of reusable code and modularity. This will ease future maintenance of these databases.
Object database capabilities such as message passing, extensibility, and the support of hierarchical structures, are important for multimedia systems.
We can develop the application fastest class definitions. ODBMSs are extensible. They allow incremental changes to the database applications.
Extensibility: Extensibility .means that the set of operations, structures and constraints that are available to operations are not fixed, and developers can define new operations, which can then be added as needed to their application.
Object-oriented software technology has three important concepts. They are:
Encapsulation: It is the ability to deal with software entities as units that interact in pre-defined and controllable manner, and where the control routines are integral with entity.
Association: It is the ability to define a software entity in terms of its di fferences from another entity. Classification: It is the ability to represent with a single software entity a number of data items that all have the same behavior and the same state attributes.
Object orientation helps to organize the software in a more, modular and re-usable manner. Encapsulation allows for the development of open systems where one part of the application does not need to know the functioning of other part. It also provides autonomy; Autonomy means we can interface to a variety of external programs can be built in one class of objects and the storage of the data in another class of objects.
Database Organization for Multimedia Applications
Data organization for multimedia systems has some key issues. They are:
(l) Data independence (2) Common distributed database architecture
(3)Distributed database servers· (4) Multimedia object management.
Flexible access by a number of databases requires that the data be independent from the application so that future applications can access the data without constraints related to a previous application.
Key features of data independent designs are:
1.Storage design in independent of specific applications.
2.Explicit data definitions are independent of application program.
3.Users need not know data formats or physical storage structures.
4.Integrity assurance in independent of application programs.
5.Recovery in independent of application programs.
Distributed Data servers
Distributed database servers are a dedicated resource on a network accessible to a number of applications. The database server is built for growth and enhancement, and the network provides the opportunity for the growth of applications and distributed access to the data.
Multimedia Object Management
The object management system must be capable of indexing, grouping and storing multimedia objects in distributed hierarchical optional storage systems, and accessing these objects on or keyed basis.
The design of the object management system should be capable indexing objects in such a manner that there is no need to maintain multiple storage copies.
Multimedia transactions are very complex transactions. We define a multimedia transaction as the sequence of events that starts when a user makes a request to display, edit, or print a hyper media document. The transaction is complete when the user releases the hypermedia document and stores back the edited versions or discards the copy in memory (including virtual memory) or local storage ..