The primary strengths of blockchain systems come from strong guarantees of immutability and reliability, and these systems can be extended with programmatic logic through Smart Contracts. Many such programmatic use cases would benefit from the use of external data. However, the method of bringing that data onto the blockchain needs to be trustworthy and secure. Otherwise, the benefits of blockchain, namely distributed trust, no single points of failure, and immutability, would be at risk. Blockchain oracles are proposed as a conceptual solution to this problem. A blockchain oracle acts as a trusted intermediary to external data. In this work we analyze existing proposals for Discernible event oracle mechanisms, which seek to address oracle queries with a broad knowledgeable answering population, to characterize problems related to the incentives imposed by external value that depends on oracle outcomes. In doing so, we focus on continued challenges to voting based oracles, including trust limitations and the need to match questions to knowledgeable answering parties. To address these difficulties, we propose an extension to existing oracle protocols to utilize reputation as a tool to measure value and as a tool to associate questions with context. By providing a method to track contextual knowledge, our proposal allows for context-based query matching and enables higher probability of correctness for a given population size as well as stronger participation incentives.

Blockchains benefit from guarantees of immutability and reliability due to their high redundancy and distributed nature. They show their value especially when operating between untrusted parties. Their functionality can be extended program-matically by smart contracts, but are limited by high costs of on-chain computation and only being able to truly trust data which is directly included on-chain. To attempt to bridge this limitation, blockchain oracles are introduced as a conceptual solution to act as a trusted source of information within the blockchain. The Oracle Problem emerges as we consider how one can introduce trusted information into a trust-free environment without compromising the validity of the blockchain. Many promising designs for oracle mechanisms have been proposed, but it is not readily apparent how one should assess the applicability of a given mechanism, nor the strengths and features between mechanisms. To be equipped to assess and categorize oracles, we must consider not just the possible answers, but the questions to which these oracles are trying to speak. Categorizing questions by their possible answering populations, we propose a framework for considering oracle questions and the context with which they are posed. We observe that there are limitations to what an oracle can hope to achieve, depending on the nature of the question, while noting the context in which a question exists can change what is viewed as true.