What is the definition of the duality group E7(7) that appears in N=8 Supergravity and what are the basics properties? Moreover what is the relation with the Lie Algebra E7?

Please, provide some reference in your answer.

1. What is the definition of the duality group $E_{7(7)}$ that appears in ${\cal N}=8$ Supergravity and what are the basics properties?

2. Moreover what is the relation with the Lie Algebra $E_7$?

3. Please, provide some reference in your answer.