A federation is a group that serves as an intermediate point between a main chain and one of its sidechains. This group determines when the coins a user has used are locked up and released. The creators of the sidechain can choose the members of the federation. A problem with the federation structure is that it adds another layer between the main chain and the sidechain.

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This segment is where we have seen the most rapid metamorphosis in the past year, mostly in financial services. These solutions are industry-specific, and they are based on private blockchain or ledger infrastructures. A caveat here is that some of these are not full blockchains. Rather, they are distributed ledgers, which are a subset of blockchain capabilities. And some don’t even include a consensus element, which takes the implementation another level down from distributed ledger tech.
Another technology that could see more widespread use in the coming years is side chains. A side chain is defined for one specific use case. There can be multiple side chains where different tasks are distributed accordingly for improving the efficiency of processing. Maybe one application needs to optimize for high speeds and another needs to optimize for large computations. In any case, side chains can be used to handle commercial blockchain usage. CryptoKitties would have greatly benefitted from an optimized high-speed side chain. At one point, they jammed up the Ethereum blockchain with 25% of all transactions coming from their application.
Using Rootstock as an example, in order to transfer assets from one chain to the other a user on the parent first has to send their coins to a special output address where they will consequently become locked and un-spendable. Once the transaction is completed, SPV then confirms it across the chains and after waiting out a contest period, which is just a secondary method to help prevent double spending, the equivalent amount will be credited and spendable on the Sidechain and vice versa.
Congratulations! You’ve just educated yourself on the most common advanced topics in blockchain that you’ll hear about. By understanding these concepts, you have a firmer grasp on the fundamental tradeoffs and latest research on the blockchain than most industry “experts”! Better yet, next time you hear your colleagues around the water cooler talking about state channels, the Lightning Network and Byzantine fault tolerance, not only will you know what they’re talking about but you might be able to teach them a thing or two!
Sometimes separate blocks can be produced concurrently, creating a temporary fork. In addition to a secure hash-based history, any blockchain has a specified algorithm for scoring different versions of the history so that one with a higher value can be selected over others. Blocks not selected for inclusion in the chain are called orphan blocks.[22] Peers supporting the database have different versions of the history from time to time. They keep only the highest-scoring version of the database known to them. Whenever a peer receives a higher-scoring version (usually the old version with a single new block added) they extend or overwrite their own database and retransmit the improvement to their peers. There is never an absolute guarantee that any particular entry will remain in the best version of the history forever. Because blockchains are typically built to add the score of new blocks onto old blocks and because there are incentives to work only on extending with new blocks rather than overwriting old blocks, the probability of an entry becoming superseded goes down exponentially[23] as more blocks are built on top of it, eventually becoming very low.[1][24]:ch. 08[25] For example, in a blockchain using the proof-of-work system, the chain with the most cumulative proof-of-work is always considered the valid one by the network. There are a number of methods that can be used to demonstrate a sufficient level of computation. Within a blockchain the computation is carried out redundantly rather than in the traditional segregated and parallel manner.[26]
Loom Network is a Platform as a Service built on top of Ethereum that allows developers to run large-scale decentralized applications. This lets developers build DApps with the trust and security of the world’s most secure public blockchain, along with the computing resources necessary to run commercial-scale services. Like how Filecoin tokenized disk space, Loom aims to be the tokenized application protocol of the new decentralized web.

“Private blockchains are valuable to solve efficiency, security and fraud problems within traditional financial institutions, but only incrementally. Private blockchains will not revolutionize the financial system. Public blockchains, however, hold the potential to replace most functions of traditional financial institutions with software, fundamentally reshaping the way the financial system works.” 

The second option will be to use sidechains. Blockstream first announced side chain in 2014 and published its whitepaper (https://blockstream.com/sidechai...). I believe in the future, bitcoin will have its desired flexibility with its sidechains. The idea of the sidechain is you can innovate and design your solution freely in the sidechains. These sidechains are independent, if they are failed or hacked, they won't damage other chains. So damage will be limited within that chain, for that reason you can be less conservative. Otherwise you would be more risk averse, if you had 42.5 billion dollar market cap like Bitcoin.
@tradles – thanks for taking the time to explain this. OK – so I get the debate around blockchain bloat and the (grudging) inclusion of OP_RETURN, etc., but what I’m missing is that I can only really see one scenario where embedding any identity data into the blockchain makes sense…. and that’s when I want to *associate* an identity with a transaction I’m performing.
A federation is a group that serves as the intermediary between a parent chain and its corresponding sidechain. It is an additional layer in the protocol but serves a key function and is what Blockstream’s Liquid sidechain uses. Due to the lack of expressiveness of Bitcoin’s scripting language, an externally implemented and mutually distrusting set of members form a federated peg.
In general, so far there has been little emphasis on the distinction between consortium blockchains and fully private blockchains, although it is important: the former provides a hybrid between the “low-trust” provided by public blockchains and the “single highly-trusted entity” model of private blockchains, whereas the latter can be more accurately described as a traditional centralized system with a degree of cryptographic auditability attached. However, to some degree there is good reason for the focus on consortium over private: the fundamental value of blockchains in a fully private context, aside from the replicated state machine functionality, is cryptographic authentication, and there is no reason to believe that the optimal format of such authentication provision should consist of a series of hash-linked data packets containing Merkle tree roots; generalized zero knowledge proof technology provides a much broader array of exciting possibilities about the kinds of cryptographic assurances that applications can provide their users. In general, I would even argue that generalized zero-knowledge-proofs are, in the corporate financial world, greatly underhyped compared to private blockchains.
Bitcoin’s block interval is ten minutes so it takes about five ten minutes on average for a new transaction to find its way into a block, even if it pays a high fee. This is too slow for some people so they have experimented with alternative cryptocurrencies, based on the Bitcoin code-base, which employ quicker block intervals   [UPDATED 2014-10-27 to correct my embarrassing misunderstanding of mathematics…]
@gendal, good question. Think of the identity hash as a bitcoin address, it is indeed public. So to assert anything with this identity you need to sign the object you are creating or changing with the identity’s private key. Specifically it is a private key that corresponds to a public key that you published in your identity’s object (json). The signature is not placed on the bitcoin transaction, as OP_RETURN has only 40 bytes. The signature is added to a [json] object that is modified with this identity. If you see any fault with this, please let me know.

Aelf uses a consensus algorithm called DPoS (Delegated Proof of Stake) that takes the best of both cooperative and competitive consensus algorithms. DPoS uses votes from stakeholders to achieve consensus. The competitive part is larger stakeholders having an influence on their delegate of choice. The delegates that have the most votes will take their turn to produce a block cooperatively in a sequence. DPoS makes transactions permanent. A rollback isn’t possible so a confirmation can be fast. DPoS is also scalable because anyone can participate in the consensus. Additionally, DPoS is environmentally friendly because electricity isn’t wasted like in Proof of Work.
Public blockchains are also expensive, and not just in terms of money. The time and energy required to process transactions on public chains is more intensive than that of non-public chains. This is because every single node on the chain must authorize each new transaction before it is added to the chain, which requires a large amount of electricity and time (not to mention money).
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Tú, o el usuario en cuestión de las sidechains, envía los bitcoins a una dirección Bitcoin específica, sabiendo que, una vez mandados, estarán fuera de tu control y fuera del control de cualquier otra persona. Estarán completamente inmovilizados y sólo se podrán desbloquear si alguien puede demostrar que no se están utilizando en ningún otro lugar.

Public blockchains are open, and therefore are likely to be used by very many entities and gain some network effects. To give a particular example, consider the case of domain name escrow. Currently, if A wants to sell a domain to B, there is the standard counterparty risk problem that needs to be resolved: if A sends first, B may not send the money, and if B sends first then A might not send the domain. To solve this problem, we have centralized escrow intermediaries, but these charge fees of three to six percent. However, if we have a domain name system on a blockchain, and a currency on the same blockchain, then we can cut costs to near-zero with a smart contract: A can send the domain to a program which immediately sends it to the first person to send the program money, and the program is trusted because it runs on a public blockchain. Note that in order for this to work efficiently, two completely heterogeneous asset classes from completely different industries must be on the same database - not a situation which can easily happen with private ledgers. Another similar example in this category is land registries and title insurance, although it is important to note that another route to interoperability is to have a private chain that the public chain can verify, btcrelay-style, and perform transactions cross-chain.
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Note: This is also a pioneering effort towards increased adoption of smart contracts because while the traditional contracts have been around for a long time, smart contracts are relatively new, and there are gaps in how they are structured. If the smart contracts have the necessary legal expressions then that could serve as a template to bridge this gap in future.

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Lisk es una plataforma open source en la que se pueden desarrollar y ejecutar smart contracts en forma de aplicaciones descentralizadas o DAPPS multiplataforma. Éstas, y como uno de los puntos fuertes de Lisk, son desarrolladas con, posiblemente, el lenguaje de programación más famoso y usado, Javascript. Aunque con un enfoque genérico, ya han empezado a aparecer algunas soluciones e interés en sectores concretos, como es el caso del Internet de las cosas que, junto a Chain of Things, están empezando a explotar.
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Things get a bit more interesting when you replace the single custodian with a federation of notaries by way of a multisignature address. In this model, a federation of entities must sign-off on movements to and from the sidechain, so more parties must be compromised for a failure situation to unfold where the bitcoins frozen on the main chain are stolen.

Sidechains, just like any other Blockchain, need their own miners to help protect them from nefarious actors and attacks which people would like to leverage against the network. However, since wealth isn't actually created on the Sidechain there is far less incentive for miners to actually work on it and help protect it. Because of this, transaction fees are the basic reward that is offered to miners. However, these often equate to mere pennies.
Public chains to the rescue! Public chains offer public transaction data that can be verified in real-time by anybody that cares to run a node. The more independent users or institutions that take part in verification, the more secure and decentralised the chain becomes! At Iryo, we strive to have every clinic doing full validation of the global state for the relevant smart contracts (EOS based). Public blockchains are mainly useful for two things; value routing (including initial creation and distribution) and trustless timestamping of messages.
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"I see quite a few use cases for private blockchains, and they definitely have their place. Traditional institutions won't switch to a completely public blockchain from one day to the other. A private blockchain is a great first step towards a more cryptographic future. The biggest advantages of private blockchains in comparison to centralized databases are the cryptographic auditing and known identities. Nobody can tamper with the data, and mistakes can be traced back. In comparison to a public blockchain it is much faster, cheaper and respects the company's privacy. As a conclusion, it's better to rely on a private blockchain than no cryptographic system at all. It has merits and pushes the blockchain terminology into the corporate world, making truly public blockchains a bit more likely for the future."