Idealistic propaganda to the contrary notwithstanding, URIs are neither unambiguous nor self-defining. A URI's meaning depends on its context of use and an implicit social contract among its minters, distributors, servers and users. Borrowing a term with origins in the ethnography of the workplace, we can say that URIs depend on a _community of practice_, the unwitting signatories to such a contract.
In this talk I will argue that as a community commited to promoting PIDs, we need to understand the implications of this view of URIs, because it also applies to (at least the actionable forms of) PIDs.
As my title suggests, there is not just one universal community of practice within which URIs are made effective (c.f. Berners Lee's "single, global information space"): there are many of them, and they do _not_ all operate by the same rules. Making a PID system work, technically, but more importantly _socially_, so that the virtuous circle of awareness, adoption and growth kicks in, requires that system to occupy a viable niche in the space of possibilities afforded by at least one _URI ecosystem_: a pattern of URI usage and the community of practice which sustains it.
