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