I tried for about 1 month to understand ABE and know I am confusing about access tree. In paper "Attributed-based encryption for fine-grained access control of encrypted data" the author explained the generation of keys with access tree for KP-ABE which I attached the picture of it here.
I found an example for this but some parts in paper are not clear for me.
1) what is the meaning of "threshold value"? Based on the top example, how can I determine this for different nodes?
2) What is the meaning of the index (x)?
Thanks a lot. I appreciate your helps.