1. Introduction
The important proliferation of digital multimedia content requires tools for extracting useful knowledge from the content to enable intelligent and efficient multimedia organization, filtering and retrieval. Knowledge is usually defined as facts about the world and is often represented as concepts and relationships among the concepts, i.e., semantic networks. Concepts are abstractions of objects, situations, or events in the world (e.g., color pattern and “car”); relationships represent interactions among concepts (e.g., color pattern 1 visually similar to color pattern 2 and “sedan” specialization of “car”).