Multimedia query and presentation algebras

In classical relational databases, we have a declarative query language called the relational calculus. Calculus queries specify what the user wishes to ask, but do not tell the system how to compute this. In contrast, the relational algebra specifies a query, together with an operational way of executing the query. Queries expressed in the declarative calculus are executed by converting the query to an algebraic query, and then optimized. The article covers two types of database-databases of multimedia objects, and databases of (possibly interactive) multimedia presentations. It shows how, for each of these types of database, we may: (i) build a query calculus, (ii) build a query algebra, and (iii) link up the two through equivalence results that may be used for optimizing queries