The purpose of this paper is to introduce and study the following graph-theoretic paradigm. Let
$$ \begin{align*}T_Kf(x)=\int K(x,y) f(y) d\mu(y),\end{align*} $$
where
$f: X \to {\Bbb R}$
, X a set, finite or infinite, and K and
$\mu $
denote a suitable kernel and a measure, respectively. Given a connected ordered graph G on n vertices, consider the multi-linear form
$$ \begin{align*}\Lambda_G(f_1,f_2, \dots, f_n)=\int_{x^1, \dots, x^n \in X} \ \prod_{(i,j) \in {\mathcal E}(G)} K(x^i,x^j) \prod_{l=1}^n f_l(x^l) d\mu(x^l),\end{align*} $$
where
${\mathcal E}(G)$
is the edge set of G. Define
$\Lambda _G(p_1, \ldots , p_n)$
as the smallest constant
$C>0$
such that the inequality
(0.1)
$$ \begin{align} \Lambda_G(f_1, \dots, f_n) \leq C \prod_{i=1}^n {||f_i||}_{L^{p_i}(X, \mu)} \end{align} $$
holds for all nonnegative real-valued functions
$f_i$
,
$1\le i\le n$
, on X. The basic question is, how does the structure of G and the mapping properties of the operator
$T_K$
influence the sharp exponents in (0.1). In this paper, this question is investigated mainly in the case
$X={\Bbb F}_q^d$
, the d-dimensional vector space over the field with q elements,
$K(x^i,x^j)$
is the indicator function of the sphere evaluated at
$x^i-x^j$
, and connected graphs G with at most four vertices.