B
The Multimedia Schema

This appendix describes the following topics:

• A Typical Multimedia Application
• The Multimedia Schema
• Table Multimedia_Tab
• Script for Creating the Multimedia Schema

A Typical Multimedia Application

Oracle9i supports LOBs, large objects which can hold up to 4 gigabytes of binary or character data. What does this mean to you, the application developer?

Consider the following multimedia scenario.

Multimedia data is used in an increasing variety of media channels -- film, television, Web pages, and CD-ROM being the most prevalent. The media experiences having to do with these different channels vary in many respects (interactivity, physical environment, the structure of information, to name a few). Despite these differences, there is often considerable similarity in the multimedia authoring process, especially with regard to assembling content.

For instance, a television station that creates complex documentaries, an advertising agency that produces advertisements for television, and a software production house that specializes in interactive games for the web could all make good use of a database management system for collecting and organizing the multimedia data. Presumably, they each have sophisticated editing software for composing these elements into their specific products, but the complexity of such projects creates a need for a pre-composition application for organizing the multimedia elements into appropriate groups.

Taking our lead from movie-making, our hypothetical application for collecting content uses the clip as its basic unit of organization. Any clip is able to include one or more of the following media types:

• Character text, such as, storyboard, transcript, subtitles
• Images, such as, photographs, video frames
• Line drawings, such as, maps
• Audio, such as, sound-effects, music, interviews

Since this is a pre-editing application, the precise relationship of elements within a clip (such as the synchronization of voice-over audio with a photograph) and between clips (such as the sequence of clips) is not defined.

The application should allow multiple editors working simultaneously to store, retrieve and manipulate the different kinds of multimedia data. We assume that some material is gathered from in-house databases. At the same time, it should also be possible to purchase and download data from professional services.

This Scenario is Only An Example

Our mission in this appendix is not to create this real-life application, but to describe some typical scenarios you may need to know about working with LOBs. Consequently, we only implement the application sufficiently to demonstrate the technology. For example, we deal with only a limited number of multimedia types. We make no attempt to create the client-side applications for manipulating LOBs.

Also we do not deal with deployment issues such as the fact that you should implement disk striping of LOB files, if possible, for best performance.

The Multimedia Schema

Figure B-1 illustrates multimedia schema used for the examples in this manual.

The Multimedia schema is comprised of the following components:

• Table Multimedia_tab
• Table VoiceOver_tab
• Nested Table INSEG_NTAB
• Column Object MAP_OBJ

Figure B-1 The Multimedia Schema

Text description of the illustration adlob033.gif

Table Multimedia_Tab

Figure B-1, "The Multimedia Schema", shows table Multimedia_tab's structure. Table Multimedia_tab columns are described in the following:

• CLIP_ID: Every row (clip object) must have a number which identifies the clip. This number is generated by the Oracle number SEQUENCER as a matter of convenience, and has nothing to do with the eventual ordering of the clip.
• STORY: The application design requires that every clip must also have text, that is a storyboard, that describes the clip. Since we do not wish to limit the length of this text, or restrict its format, we use a CLOB datatype.
• FLSUB: Subtitles have many uses -- for closed-captioning, as titles, as overlays that draw attention, and so on. A full-fledged application would have columns for each of these kinds of data but we are considering only the specialized case of a foreign language subtitle, for which we use the NCLOB datatype.
• PHOTO: Photographs are clearly a staple of multimedia products. We assume there is a library of photographs stored in the PhotoLib_tab archive. Since a large database of this kind would be stored on tertiary storage that was periodically updated, the column for photographs makes use of the BFILE datatype.
• FRAME: It is often necessary to extract elements from dynamic media sources for further processing For instance, VRML game-builders and animation cartoonists are often interested in individual cells. Our application takes up the need to subject film/video to frame-by-frame analysis such as was performed on the film of the Kennedy assassination. While it is assumed that the source is on persistent storage, our application allows for an individual frame to be stored as a BLOB.
• SOUND: A BLOB column for sound-effects.
• VOICED_REF: This column allows for a reference to a specific row in a table which must be of the type Voiced_typ. In our application, this is a reference to a row in the table VoiceOver_tab whose purpose is to store audio recordings for use as voice-over commentaries. For instance, these might be readings by actors of words spoken or written by people for whom no audio recording can be made, perhaps because they are no longer living, or because they spoke or wrote in a foreign language.

  This structure offers the application builder a number of different strategies from those discussed thus far. Instead of loading material into the row from an archival source, an application can simply reference the data. This means that the same data can be referenced from other tables within the application, or by other applications. The single stipulation is that the reference can only be to tables of the same type. Put another way: the reference, Voiced_ref, can refer to row objects in any table which conforms to the type, Voiced_typ.

  Note that Voiced_typ combines the use of two LOB datatypes:

  • CLOB to store the script which the actor reads
  • BFILE for the audio recordings.
• INSEG_NTAB: While it is not possible to store a Varray of LOBs, application builders can store a variable number of multimedia elements in a single row using nested tables. In our application, nested table InSeg_ntab of predefined type InSeg_typ can be used to store zero, one, or many interview segments in a given clip. So, for instance, a hypothetical user could use this facility to collect together one or more interview segments having to do with the same theme that occurred at different times.

  In this case, nested table, interviewsegments_ntab, makes use of the following two LOB datatypes:

  • BFILE to store the audio recording of the interview
  • CLOB for transcript

  Since such segments might be of great length, it is important to keep in mind that LOBs cannot be more than 4 gigabytes.

• MUSIC: The ability to handle music must be one of the basic requirements of any multimedia database management system. In this case, the BFILE datatype is used to store the audio as an operating system file.
• MAP_OBJ: Multimedia applications must be able to handle many different kinds of line art -- cartoons, diagrams, and fine art, to name a few. In our application, provision is made for a clip to contain a map as a column object, MAP_OBJ, of the object type MAP_TYP. In this case, the object is contained by value, being embedded in the row.

  As defined in our application, MAP_TYP has only one LOB in its structure -- a BLOB for the drawing itself. However, as in the case of the types underlying REFs and nested tables, there is no restriction on the number of LOBs that an object type may contain.

Script for Creating the Multimedia Schema

Here is the script used to create the Multimedia schema:

CONNECT system/manager;
DROP USER samp CASCADE;
DROP DIRECTORY AUDIO_DIR;
DROP DIRECTORY FRAME_DIR;
DROP DIRECTORY PHOTO_DIR;
DROP TYPE InSeg_typ force;
DROP TYPE InSeg_tab;
DROP TABLE InSeg_table;
CREATE USER samp identified by samp;
GRANT CONNECT, RESOURCE to samp;
CREATE DIRECTORY AUDIO_DIR AS '/tmp/';
CREATE DIRECTORY FRAME_DIR AS '/tmp/';
CREATE DIRECTORY PHOTO_DIR AS '/tmp/';
GRANT READ ON DIRECTORY AUDIO_DIR to samp;
GRANT READ ON DIRECTORY FRAME_DIR to samp;
GRANT READ ON DIRECTORY PHOTO_DIR to samp;
CONNECT samp/samp
CREATE TABLE a_table (blob_col BLOB); 
CREATE TYPE Voiced_typ AS OBJECT ( 
   Originator      VARCHAR2(30), 
   Script          CLOB, 
   Actor           VARCHAR2(30),  
   Take            NUMBER,
   Recording       BFILE 
);

CREATE TABLE VoiceoverLib_tab of Voiced_typ (
Script DEFAULT EMPTY_CLOB(),
   CONSTRAINT TakeLib CHECK (Take IS NOT NULL),
   Recording DEFAULT NULL
);

CREATE TYPE InSeg_typ AS OBJECT ( 
   Segment         NUMBER, 
   Interview_Date  DATE, 
   Interviewer     VARCHAR2(30),  
   Interviewee     VARCHAR2(30),  
   Recording       BFILE, 
   Transcript      CLOB 
);

CREATE TYPE InSeg_tab AS TABLE of InSeg_typ;
CREATE TYPE Map_typ AS OBJECT (
   Region          VARCHAR2(30),
   NW              NUMBER,
   NE              NUMBER,
   SW              NUMBER,
   SE              NUMBER,
   Drawing         BLOB,
   Aerial          BFILE
);
CREATE TABLE Map_Libtab of Map_typ;
CREATE TABLE Voiceover_tab of Voiced_typ (
Script DEFAULT EMPTY_CLOB(),
   CONSTRAINT Take CHECK (Take IS NOT NULL),
   Recording DEFAULT NULL
);

Since one can use SQL DDL directly to create a table containing one or more LOB columns, it is not necessary to use the DBMS_LOB package.
CREATE TABLE Multimedia_tab ( 
   Clip_ID         NUMBER NOT NULL, 
   Story           CLOB default EMPTY_CLOB(), 
   FLSub           NCLOB default EMPTY_CLOB(), 
   Photo           BFILE default NULL, 
   Frame           BLOB default EMPTY_BLOB(), 
   Sound           BLOB default EMPTY_BLOB(), 
   Voiced_ref      REF Voiced_typ,
   InSeg_ntab      InSeg_tab, 
   Music           BFILE default NULL, 
   Map_obj         Map_typ 
 ) NESTED TABLE    InSeg_ntab STORE AS InSeg_nestedtab; 

This script is also located in $HOME Oracle9i "demo" directory in the following files: