Relational database systems solve many of the traditional problems for processing of structured data. However, unstructured data in the form of images, video, audio and multimedia is growing at a tremendous rate and introduces new requirements that are not met by today's database engines. One well known example is content-based retrieval that involves similarity searching and indexing in high-dimensional feature spaces. In addition there has been much recent focus on applying machine learning techniques involving semantics modeling, spatio-temporal indexing, multi-modal (audio-, visual-, textual-) integration and relevance feedback searching.