Subject: Multimedia System

Topic: Multimedia Databases

Difficulty: Medium

Architecture of a multi-user database can become complex. It is not clear which architecture would be the best option for a multimedia database. A transaction involving multimedia data will in general be expected to take longer. Locks will have to be maintained for longer periods. MDBMS (Multimedia Database Management System) has formal database architecture. It has a separate user view from the system view

MMDBs require all the basic attributes of a database management system such as a transaction manager, query optimizer, recovery manager etc. as well as special storage structures and specialized search and querying modules.

Typical architecture of a MMDB application

Since existing relational and OO databases comprise the basic requirements of any database, it is natural that many multimedia and imaging DB applications are constructed within such existing systems. In order to support such applications, many DBMS vendors offer facilities suitable for MM.

These include:

• long bit and byte strings
• BLOBS
• Paths or references of images where the actual image stored elsewhere, such as on an optical storage subsystem.

The reasons for this are that document imaging systems need on-line, near-line and off-line storage of images, including archiving. This may be achieved by the use of optical jukeboxes but most commercial DBMSs do not directly support optical storage subsystems (Informix Online/optical is an exception).

Content retrieval capabilities. In conventional relational and OO DBs querying is based on the attributes of objects. However, information retrieval and document imaging systems require searching the content of documents. This ability can be generalized to still images, audio and video.

Multimedia Database basically constitutes a three layer architecture. A simple representation is shown below:

Interface

The interface between the user and the database is used for the following activities:

• Object browsing
• Compose
• Dispose

Object Composition

The object composition part of the multimedia database manages the multimedia objects

Storage

Storage functions of multimedia database involve clustering and indexing of multimedia data.

Three-layer architecture

Database (Data) Tier − At this tier, the database resides along with its query processing languages. We also have the relations that define the data and their constraints at this level.

Application (Middle) Tier − At this tier reside the application server and the programs that access the database. For a user, this application tier presents an abstracted view of the database. End-users are unaware of any existence of the database beyond the application. At the other end, the database tier is not aware of any other user beyond the application tier. Hence, the application layer sits in the middle and acts as a mediator between the end-user and the database.

User (Presentation) Tier − End-users operate on this tier and they know nothing about any existence of the database beyond this layer. At this layer, multiple views of the database can be provided by the application. All views are generated by applications that reside in the application tier.