Let S be a schema, which is a set of streams and multimedia streams S:{Si}. Each stream Si consists of a set of attributes of a certain predefined type Ti, where the type could be any traditional data type (such as number, string, boolean, timestamp, etc) or any multimedia data type (Micon), such as: icon (image), earcon (audio), vicon (video), etc. Formally: Si = {Xi | 0=< i =< n and Xi is of Type Ti}

A multimedia continuous query (m-CQ) is a computational structure or graph - that could be seen as a network of operators - that consists of a set of nodes representing the operators, and a set of edges indicating the data flow from one operator to another. Each m-CQ should have at least one input multimedia stream, and exactly one output stream.