Multimedia Databases

Metadata can often be stored in relatively standard relational and object oriented structures and can be easily queried though simple extension of languages such as SQL.

Type of Metadata :

• Content Independent Metadata : this type of metadata captures information that does not depend on content of document with which it ios associated. Example of this type of metadata are : owner,location, modification date of document. There is no information content captured but still such metadata is useful for retrival of documents.
• Content dependent Metadata : Example is size of document,number of rows and columns and othre field which depend upon content. This can be further sub-divided in two :
  
• Direct Content Base Metadata : This is based directly on content of document. A popular example is "index for a document" .
  
• Content Descriptive Metadata : This type of metadata describes the content of document without direct utilization of those contents.Example is "texual anonations describing an image".
  

Now here is how can we formally define metadata :

A media-instance is an 8-tuple
(ST, fe, ATR, A, R, F, Var1, Var2)
where:
ST is a set of objects called states, and
fe is a set of objects called features, and
ATR is a set of objects called attribute values, and
A is a map from states to sets of features, and
R is a set of relations on fe^i * ST for i > 0, and
F is a set of relations on ST, and
Var1, is a set of objects, called variables, ranging over ST, and
Var2, is a set of variables ranging over fe.

A state is smallest chunk of media data that we wish to consider. For example , in an image database each eimage may be viewed as state.
A feature is any object in a state that is of interest for multimedia database. Example for an image pic.gif showing car, the feature of pic.gif is car .
The Attributes are properties of features in a state. like for picture of car the attributes may be car color, model.
A is a feature extraction ap which tells which feature occur in which states.
R is set of relation on fe X ATR X ST --those relations are state dependent. for instance for an omage photo.gif. There may be state dependent relation ship called left_of containg tuples like (a , b , photo.gif) such that a is in left of b in photo.gif.
F is a relation on states like "before" example for such relation is (a.gif , b.gif) such that acc to before relation , photo a.gif was taken before b.gif.

Having this formal representation now we can easily formulate methods for queying database easily. Now we cab define functions like : FindObjectWithFeature(a) , this wll search database for all such states with feature containg a. Or we can list all features of an image with FindFeatures() . Other function types can be FindObjectWithFeatureandAttr(Jane,suit,blue) this query asks to find all media objects in which jane apperars in a blue suit. the above mentioned functions are available by default in SMDS-SQL. An example query is "find all images containg jane and denis , with jane to left of Denis.
SELECT M
FROM smds source1 M
WHERE FindType(M) = Image AND
M in FindObjWithFeature(Denis) AND
M in FindObjWithFeature(jane ) AND
left(jane,denis,M)