I am a beginner in these different standards.

I am looking for answers to very basic questions.

1. Why do we need different graphics standards like Open GL, Open GL ES, Open VG? Why can't one single standard serve the purpose?

2. What are the differences between OpenGL and OpenVG? I suppose both the standards can deal with 2D graphics.

3. From my understanding, OpenVG supports both raster and vector graphics. What do OpenGL support?

4. Are there any resources that gives a pictorial or clear understanding on where Open GL, Open GL ES and Open VG stand in terms of graphics?