Definition 1. A Data Stream is a sequence of tuples according to a certain schema that keeps arriving to a Data Stream Management System. Tuples could be of one out of three types: add, delete and the update tuples. Each tuple has both a unique identifier and a timestamp that is used to order the tuples.

Definition 2. A Micon is a multimedia icon that could be: text (ticon), still image (icon), audio (earcon), video (vicon), or a set of the Micons.