The Idea of Smart Contracts (1997)

Another example, of course, would be digital rights management. Interestingly, DRM's high-water mark (from the perspective of those who insisted on it) began shortly after this article was written, when it was formalized by the DMCA’s anti-circumvention provisions. As the author would say, this helped to enhance the costs of “breaching” the DRM’s contract. (In the same way, laws against vandalism and petty theft enhance the costs of “breaching” the vending machine’s contract.)

We're building such a system here: http://orisi.org/ and there's a whitepaper available here - https://github.com/orisi/wiki/wiki/Orisi-White-Paper

A similar system could be used for Ethereum as well, to bring external inputs into the mix.