Multimedia Data

Multimedia Data

One of the important trends in database systems is the addition of multimedia data. By "multimedia" we mean information that represents a signal of some sort. Common types of multimedia data include video, audio, radar signals, satellite images, and documents or pictures in different encodings. These forms have in common that they are much larger than the earlier forms of data-integers, character strings of fixed length, and so on, and of very much different sizes.

The storage of multimedia data has forced DBMS's to expand in various ways. For example, the operations that one performs on multimedia data are not the simple ones appropriate for traditional data forms. Thus, while one might search a bank database for accounts that have a negative balance, comparing each balance with the real number 0.0, it is not practicable to search a database of pictures for those that show a face that "looks like" a specific image.

To allow users to create and use difficult data operations such as image-processing, DBMS's have had to integrate the ability of users to introduce functions of their own choosing. Often, the object-oriented approach is used for such extensions, even in relational systems, which are then dubbed "object- relational". We shall take up object-oriented database programming in different places including "Other Data Models" and "Object-Orientation in Query Languages".
 
The size of multimedia objects also forces the DBMS to change the storage manager so that objects or tuples of a gigabyte or more can be accommodated. Among the various problems that such large elements present is the delivery of answers to queries. In a conventional, relational database, an answer is a set of tuples. These tuples would be delivered to the client by the database server as a whole.

However, assume the answer to a query is a video clip a gigabyte long. It is not practicable for the server to deliver the gigabyte to the client as a whole. For one reason it takes too long and will stop the server from handling other requests. For another, the client may want only a small part of the film clip, but doesn't have a way to ask for exactly what it wants without seeing the early portion of the clip. For a third reason, even if the client wants the whole clip, perhaps in order to play it on a screen, it is enough to deliver the clip at a  fixed rate over the course of an hour (the amount of time it takes to play a gigabyte of compressed video). Thus, the storage system of a DBMS supporting multimedia data has to be prepared to deliver answers in an interactive mode, passing a piece of the answer to the client on request or at a  fixed rate.




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