Tutorial: Blockchain Technologies and the Semantic Web Blockchain meets Semantic Web … ·...

Tutorial: Blockchain Technologies and the Semantic Web

Blockchain meets Semantic WebLuis-Daniel Ibáñez – University of Southamptonl.d.ibanez@soton.ac.uk

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WebGoals – Review and Discuss

› Semantic Web for Blockchains– How Semantic Web could help Blockchains?

› Blockchains for Semantic Web– How Blockchains could help Semantic Web?

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WebAgenda (Approximate)

› Semantic Web for Blockchains– Knowledge Representation (15m)– Interoperability (15m)– Discussion (10m)

› Blockchains for Semantic Web– Trust & Proof layers (15min)– Data Marketplaces and incentives (15min)– Discussion (10min)

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Distributed Systems

Cryptography

Game Theory

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WebA Blockchain Ecosystem

Community (Users and/or miners)

Consensus protocol intransaction order and validity

Incentive

Blockchain (Database)

SemWeb for Blockchains

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WebKnowledge Representation

› Blockchains started as very low level artefacts

› But now have several layers of information

› How to represent them and their contents?

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J. Pfeffer - Eth0n and Beyond – Keynote to International Workshop on Linked Data and Distributed Ledgers 2017

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J. Pfeffer - Eth0n and Beyond – Keynote to International Workshop on Linked Data and Distributed Ledgers 2017

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● On statements about blockchains● On statements asserted inside blockchains

– Proof and Trust. We’ll see that later

Reasoning possibilities!

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● Provide the right level of abstraction● Represent concepts that vary from blockchain to

blockchain– Consensus algorithm used– “Transaction”– Participant versus validator/miner

Challenges

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H. Ugarte. A more pragmatic Web 3.0 – Linked Blockchain Data

● Aimed at describing Bitcoin and Ethereum● Account, Block, Transaction, Payload

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● Ethereum specific

https://ethon.consensys.net/

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P. Tasca & C. Tessone Ontology of Blockchain Technologies, principles of Identification and Classificationhttps://dx.doi.org/10.2139/ssrn.2977811

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http://www.untitled-inc.com/the-token-classification-framework-a-multi-dimensional-tool-for-understanding-and-classifying-crypto-tokens/

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WebBlockchain Interoperability

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WebBlockchain Interoperability

● Heterogeneity of– Data (Like in Linked Data)– Communities (Like in content production networks) – Protocols– Incentives

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WebOne chain to rule them all...

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WebNot happening...

● Throughput limits● Variety of use cases

– Miners or participants, privacy and cryptography requirements

● Natural competition● Fear of becoming centralized again

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WebWhat happens though is...

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Data Silos

Blockhain Silos

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WebQuestions...

● How to use RDF et al. as a mean for data interoperability for Blockchains?

● How to enable interoperation at transaction level?

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WebData Interoperability

● One half: Lifting blockchains● Other half: Put RDF inside blockchains

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WebAdding data in Blockchains (1)

● Many Blockchains are space constrained– Most of them were not designed for this

● How to add data directly on them?

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Attaching Semantic Metadata to Cryptocurrency Transactions. Ibáñez et al. DeSemWeb 2017

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WebComparison of compression approaches

Attaching Semantic Metadata to Cryptocurrency Transactions. Ibáñez et al. DeSemWeb 2017

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● Hashing-out– Store a hash in the Blockchain, document somewhere else– Document can be verified against the hash.

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hash#x9567hh31335

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hash#x9567hh31335

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● Substitute location-based addressing for content-based addressing.

● S/Kademlia DHT + Git + BitTorrent

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https://medium.com/textileio/whats-really-happening-when-you-add-a-file-to-ipfs-ae3b8b5e4b0f

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Reconstruct document via Link Traversal

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● If not enough nodes hosting, no content● Incentives needed (more on that later)

Tradeoff

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WebTransaction interoperability

Blockchain ABlockchain B

Transact asset

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WebBlockchain Interoperability (BI)

Smart Contract@ Blockchain A

Smart Contract@ Blockchain B

Mutual call that preserves properties on both sides

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WebBlockchain Interoperability (BI)

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WebCosmos

› “TCP for Blockchains”

› Zones are regular blockchains

› A Hub that uses a consensus protocol to connect them

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WebPolka Dot

› Parachains, similar to hubs but market-controlled

› Special protocol to handle inter-consensus

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WebCrosses the SemWeb boundary, but...

● Have we ever thought on transactions in Linked Data at web scale?

● What consistency guarantees beyond Eventual Consistency?

● LD-Scripts and services executing all over the place?

● This type of constructions could be used for “adding consistency to the Web”

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Some open problems

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● Highlight Blockchains that are compatible/incompatible

● Explain possible property loss when plugging to other blockchains

Reasoning on Blockchain descriptions

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● Given a collection of interdependent Smart Contracts and a set of Blockchain ecosystems, where to deploy each piece?

● Similar to Multi-Cloud deployment

Deployment of Smart Contracts

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● A Blockchain ecosystem may die● Or become too expensive● How to migrate to another ecosystem?

Migration of Blockchains

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● Who decides on changes in the protocol● Two hackers in Zug sipping Chai Latte?● A Foundation incorporated in Singapore?● The community? How?

Governance

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● Do you see any other problems?

Discussion

Blockchains for SemWeb

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● Trust & Proof– Those layers of the Semantic Web cake…– We will see applications to Semantic Log Auditing and Scholar

Publication

● Incentives for publishing and maintaining data– Subsidies don’t scale

Problems of Semantic Web

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“The Logic layer enables the writing of rules while the Proof layer executes the rules and evaluates together with the Trust layer mechanism for applications whether to trust the given proof or not.”

Trust & Proof

https://www.w3.org/2001/12/semweb-fin/w3csw

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WebTrust and proof

Example applications

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Semantic Audit Logs

Use L2TAP ontology

Sutton & Samavi. Blockchain Enabled Privacy Audit Logs. ISWC 2017

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Semantic Audit Logs

How to protect against collusion to tampering?

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WebExperimental Evaluation

Bottomline: Linear in the size of the log

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Preserving Government Decisions

● Use case for Greek government decisions● Problem 1: They are not machine readable nor

easily verifiable– That is solved with Linked Data

● Problem 2: No one trust them, fear that decisions may be overruled unlawfully– Blockchains kick in

Beris & Koubarakis. Modeling and Preserving Greek Government Decisions using Semantic Web Technologies and Permissionless Blockchains. ESWC 2018

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Preserving Government Decisions

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Enabled provable checks

● A timestamp proves that a message existed prior to some point in time; is a “proof-of-existence”

● Input: a decision– It was stamped on date dt– Does not match anything stamped

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Decentralised Scholarly Communication● Scientific publishing is centralised

– Many researchers dislike that

● Decentralised models have been proposed– Authors self-publish articles– Articles are semantic entities (SPAR ontologies)– (Open) Reviews are also self-published and linked to articles

● Problem– We killed the monster… but we can be monsters too...

Hoffman et al. Smart Papers – Dynamic Publications on the Blockchain. ESWC 2018

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Collapse of Trust (1)

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Approach – Papers as Smart Contract● A paper is a Ethereum Smart Contract● Functions for all paper interactions

– Publish– AddReview

● Statements about papers and their links are stored as transactions in Ethereum

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Evaluation● Time to commit

– Few minutes.

● Cost– Fluctuates according to Ethereum market– 2$ per call (when measured, nowadays is less)

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Pattern for applications● Shift trust from a central entity to trust in a

Blockchain ecosystem [Protocol + Participants + Incentives + Crypto-primitives]

● Evaluate cost and risks– Public blockchains have more participants, but you have to pay in

cryptocurrency– Private blockchains require participants to put the resources to run

the protocol

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P. Evans-Greenwood. Blockchains and Linked Data. Keynote to Workshop on Linked Data and Distributed Ledgers @ WWW2017

Pathways to trust

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Paid in Cryptocurrency Paid in your hardware running the protocol

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Some open problems

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General RDF verification● Hands-on session!

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What do we want when querying?● SELECT ?s ?o

WHERE { ?s ex:pred ?x SERVICE <A_Blockchain>{ ?x ex:other_pred ?s}

}● SELECT ?s ?o

WHERE { ?s ex:pred ?x . { ?x ex:other_pred ?s} IS VERIFIED

} (Output explains who verifies and where)

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Smart Contracts as Web Services● With very special properties (and costs) ● True or False?

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Discussion● Any further problems● Questions?

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Incentives for a data economy

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WebIn contrast to the traditional web where

advertisement fueled a lot of the growth. This raises the question how the WoD can

● (i) maintain its success when government subsidies disappear and

● (ii) convince commercial entities to share their wealth of data

T. Grubenmann et al. Decentralizing the Semantic Web: Who will pay to realize it? DeSemWeb 2017

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Storage Query Pricing Exchange

Steps of selling data

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● Decentralising these steps● Adding trust/proof to these steps● Powering incentive mechanisms through

cryptocurrencies

Blockchains can help...

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● If not enough nodes hosting, no content● Incentives needed (more on that later)

Tradeoff

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● If not enough nodes hosting, no content● Incentives needed (more on that now)

FileCoin

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● A decentralized storage network that is auditable, publicly verifiable and designed on incentives.

● Clients pay a network of miners for data storage and retrieval; miners offer disk space and bandwidth in exchange of payments.

● Miners receive their payments only if the network can audit that their service was correctly provided.

FileCoin

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● An interactive proof system in which a prover defends a publicly verifiable claim that it is dedicating unique resources to storing one or more retrievable replicas of a data file

Proofs of replication

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● How to query a Web of Data stored in this?– Does querying like on P2P works?– Link Traversal?

● There are alternatives in the market (Sia,Storj)– Follow links across systems?

Querying is ongoing work

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● Given a query on a database, put a price on it● It’s a hard problem

– If you want it arbitrage-free is very hard– Or you can leave everyone set their own price, but that has other

implications

Pricing

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WebOcean Protocol

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● Privacy (Multi-Party Computation Revival)● Data Protection

– Immutability vs right to be forgotten

● Sell processing without a middle man● Use a Smart Contract to deliver

– What should go on the Blockchain and what should not?

Some open problems

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Take-aways

● SemWeb technologies are already been used for interoperability by practitioners.– Let’s keep pushing that

● Blockchains provide decentralised “Trust & Proof” machinery– Trust the protocol/ecosystem/incentive in provide proof of something– An opportunity to re-decentralise the Web.

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Tutorial: Blockchain Technologies and the Semantic Web Blockchain meets Semantic Web … ·...

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