Positive representations of $C_0(X)$. I

We introduce the notion of a positive spectral measure on a $σ$-algebra, taking values in the positive projections on a Banach lattice. Such a measure generates a bounded positive representation of the bounded measurable functions. If $X$ is a locally compact Hausdorff space, and $π$ is a positive representation of $C_0(X)$ on a KB-space, then $π$ is the restriction to $C_0(X)$ of such a representation generated by a unique regular positive spectral measure on the Borel $σ$-algebra of $X$. The relation between a positive representation of $C_0(X)$ on a Banach lattice and -- if it exists -- a generating positive spectral measure on the Borel $σ$-algebra is further investigated; here and elsewhere phenomena occur that are specific for the ordered context.