I'm unclear how this is any different from a centralized mongodb as a service platform. It seems that it doesn't offer any proof of work related security or consensus building other than a centralized "trust our cluster" policy [1].
BigchainDB targets giving the following benefits beyond traditional database as a service:
1. decentralized - no single entity controls it, which means tolerant to malicious / Byzantine faults. Benefit: groups that don't necessarily trust each other can share infrastructure.
2. immutable - which practically speaking means more tamper resistant, e.g. it's append only. Benefit: well-defined provenance for history of assets, data, etc.
3. assets - you can create and issue assets, where you own them if you have the private key. How: each tx is signed. Benefit: moving around assets on a substrate that no single entity owns or controls. Lower friction in exchanges. And the digital signatures gives cryptographic proof that about who did what.
These are the targets. We're not fully there yet. Most notably, we still need to address some Byzantine faults as our docs ([1] above) mention. This will come in an upcoming release. We are also working on improved scalability while maintaining the security guarantees [2].
Re consensus: BigchainDB has a two-layer consensus, as follows.
* The lower layer directly uses MongoDB's consensus (which it builds on) to agree on whether a transaction should be stored.
* The higher level has federation-style voting on whether a transaction is valid or not.
Our documentation describes this further.
BigchainDB is explicitly not trying to do Bitcoin-style proof of work. PoW solves for an additional problem: (theoretical) anonymity of servers. That additional goal compromises scale. And, in practice you know who's running the servers anyway (ie big Chinese Bitcoin miners), which is why I say "theoretical". BTW I am a fan of Bitcoin, it just has different goals than BigchainDB.
[2] https://blog.bigchaindb.com/bigchaindb-developer-update-2d32...
> Not sure whether BigchainDB implements consensus/PoW
It has a 2-layer consensus algorithm. (See a comment above, or BigchainDB docs.) It does not use PoW because PoW is inefficient; BigchainDB doesn't target applications needing Sybil tolerance.