Four systems have so far implemented the algebra described in this chapter. [44] developed a system called nViZn, which used the algebra to present interactive graphics in a Web environment. [29] used the algebra to structure and display data in a real-time streaming environment; their system is called Dancer. [45] developed a server-based presentation graphics system with an XML schema for GOG; this system is called. ViZml. [37] used the algebra to develop a visualization front-end for an OLAP; their system is called Polaris.