2D Z-string: A new spatial knowledge representation for image databases

The knowledge structure called the 2D C⁺-string, proposed by Huang et al., to represent symbolic pictures allows a natural way to construct iconic indexes for images. According to the cutting mechanism of the 2D C⁺-string, an object may be partitioned into several subparts. The number of partitioned subparts is bounded to O(n²), where n is the number of objects in the image. Hence, the string length is also bounded to O(n²). In this paper, we propose a new spatial knowledge representation called the 2D Z-string. Since there are no cuttings between objects in the 2D Z-string, the integrity of objects is preserved and the string length is bounded to O(n). Finally, some experiments are conducted to compare the performance of both approaches.