Database management systems have been extensively used for more than 30 years as a standard tool for manipulating large amounts of alphanumeric data. They allow efficient and fast access to stored data taking the advantage of the fact that data is structured. With the emergence of the Web, large volumes of unstructured data have become available. As database management systems were not capable of storing and searching that data efficiently, information retrieval systems took over, providing search methods for unstructured textual documents. However, with further emergence of the Web and multimedia the importance of systems that can manage and search audio-visual data has arisen.