Integrating an external data-source with a blockchain solution is usually not an easy task. The major problem is that smart-contract systems can not directly call an external data source, because if different peers at evaluating the external data source see different pieces of data, they can not come to a consensus. So external data integration requires certainly solving some technological challenges. However even at considering the use-case and the general architecture, there are some questions that can be raised:
1. Decentralization model of the blockchain: depending on the use-case, systems can be built up to totally public and consortium blockchains as well.
2. Trust model of the oracle: in certain use-case we might as well say that there is one trusted data-source, custodian oracle, that we trust. There might be the case however that we want to integrate data from multiply data-sources in a way that no single data-source is trusted. Such a system can be implemented with the help of a game theoretical approach, usually Schelling point, providing a fully decentralized oracle algorithm. Such systems are realized for example by the prediction markets, ike Augur or Gnossis.
3. Trust of the communication medium: the communication medium is usually the internet that is pretty much untrusted, meaning that there is a need for both encrypting the data and preventing tampering, with like message authentication or authenticity proofs. There might be the case however, that we trust in the communication medium. As an example, if the oracle is an IoT source that is hosted by the same cloud provider as our consortium blockchain, we might as well can trust the communication.