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I was wondering if there was a resource that listed known algebraic groups and their corresponding coordinate rings.

Edit: The previous wording was terrible.

Given an algebraic group $G$, with Borel subgroup $B$ we can form the Flag Variety $G/B$ which is projective. I am hoping for a list of the graded ring $R$ such that $Proj(R)$ corresponds to this Flag Variety.

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    @BBischof, I am not sure what the form of the ideal answer you expect will be. Obviously one can "list" such things using Dynkin diagrams (plus a choice of positive weight, corresponding to a projective embedding), since the complete flag variety $G/B$ depends only on the Dynkin diagram of $G$. But presumably you want a list that contains more information. So, you want generators and relations? A homogeneous basis for each such graded ring, together with a rule for multiplication? It's not clear to me yet.2012-08-16

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You probably mean for $G$ to be a reductive group. Keep in mind that $G/B$ is equal to $\text{Proj}(R)$ for many different $R$'s, corresponding to different embeddings of $G/B$ into projective space. The best object to study is the homogeneous coordinate ring (also known as the Cox ring) of $G/B$. In that case, when $G = SL_n$, the homogeneous coordinate ring is in Miller and Sturmfels' Combinatorial Commutative Algebra Chapter 14. For the general case, some keywords to look for are "standard monomial theory", "straightening laws", and "Littelmann path model". The homogeneous coordinate ring of a general $G/B$ (or at least $G/P$ for $P$ a maximal parabolic) might be in Lakshmibai and Raghavan's Standard Monomial Theory: Invariant Theoretic Approach, but I am not sure. Regardless, that is a good introduction to the subject and should have a fairly comprehensive list of references for further information.