What difference you feel about Arago and Yocto project?


I bought a TI Sitara AM3358 Starter Kit one year more ago. I went through TI SDK and got familiar with its TFTP, remote debug etc.
Now I find that many BeagleBone example projects on line. On the web, I notice that BeagleBone Black and other BB boards use Yocto image, not TI SDK.I see the link below:


talks a little about the SDK(Arago) and Yocto. I am still not clear about so many names. What do you think about these two projects: Arago and Yocto, if we only say Yocto for TI chip here.