Linked data indexing of distributed ledgers
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Linked Data Indexing of Distributed Ledgers provides an overview of indexing blockchain data as Linked Data to allow for richer querying and connections to external data sources. It discusses using ontologies to represent blockchain concepts and transactions as RDF, and an architecture with an Ethereum listener that extracts metadata and stores it in an RDF triplestore. Challenges include developing a distributed rather than centralized index and addressing the need for universal resource identifiers when representing blockchain data as Linked Data.
![Reputation Contract
Functions:
Storage:
sendReputation
getPersonBalance()
getReputationAttribute
attribs[address = > Attrib]
Attrib { uint balanceOf;
mapping(string => uint);
string[] attribStrings
}
Reputation
Attribute
token
Balances
Reputation Smart Contract
Tokens left
to assign
My Reputation
Peer Reputation Page
Kevin’s Reputation View
Communication: 14
Collaboration: 06
Organisation: 12
Ethics: 05
Problem Solving: 10
Engagement: 04
your Ethereum address
password to private key
Signing this transaction will transfer stated
Reputation Tokens + ETH gas payment from
your account. Estimated gas cost is 0.02 ETH.
Maximum gas cost is set to 0.05 ETH
Transfer
Reputation Tokens Left: 57
number of tokens to transfer
Assign Reputation
My Reputation
Peer Reputation Page
Michelle’s Reputation View
Communication: 06
Collaboration: 02
Organisation: 10
Ethics: 12
Problem Solving: 08
Engagement: 16
your Ethereum address
password to private key
Signing this transaction will transfer stated
Reputation Tokens + ETH gas payment from
your account. Estimated gas cost is 0.02 ETH.
Maximum gas cost is set to 0.05 ETH
Transfer
Reputation Tokens Left: 68
number of tokens to transfer
Assign Reputation
Signed
TX
Reputation
Attribute
token
Balances
Tokens left
to assign
Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin](https://image.slidesharecdn.com/linkeddataindexingofdistributedledgers-170404034633/85/Linked-data-indexing-of-distributed-ledgers-7-320.jpg)
Linked data indexing of distributed ledgers
- 1. Linked Data Indexing of Distributed Ledgers Allan Third and John Domingue (@johndmk) Knowledge Media Institute The Open University, UK http://blockchain.open.ac.uk/
- 2. Agenda • Motivation • Ethereum Model • Ontologies • Architecture • RDF examples • Smart Contracts • Challenges, Future Work and Summary
- 3. Motivation
- 4. Blockchain is a Linked List A blockchain actually contains two different hash structures. The first is a hash chain of blocks that links the different blocks to one another. The second is internal to each block and is a Merkle Tree of transactions within the blocks. This allows for efficiently verifiable proofs that a transaction was included in a block.
- 5. Contracts in Ethereum Maintain a data store representing something which is useful to either other contracts or to the outside world Serve as a sort of externally owned account with a more complicated access policy Manage an ongoing contract or relationship between multiple users Provide functions to other contracts; essentially serving as a software library. Contracts in Ethereum generally serve 4 purposes: source: Richard Gendal Brown “A Simple Model for Smart Contracts” http://gendal.me/2015/02/10/a-simple-model-for-smart-contracts/
- 7. Reputation Contract Functions: Storage: sendReputation getPersonBalance() getReputationAttribute attribs[address = > Attrib] Attrib { uint balanceOf; mapping(string => uint); string[] attribStrings } Reputation Attribute token Balances Reputation Smart Contract Tokens left to assign My Reputation Peer Reputation Page Kevin’s Reputation View Communication: 14 Collaboration: 06 Organisation: 12 Ethics: 05 Problem Solving: 10 Engagement: 04 your Ethereum address password to private key Signing this transaction will transfer stated Reputation Tokens + ETH gas payment from your account. Estimated gas cost is 0.02 ETH. Maximum gas cost is set to 0.05 ETH Transfer Reputation Tokens Left: 57 number of tokens to transfer Assign Reputation My Reputation Peer Reputation Page Michelle’s Reputation View Communication: 06 Collaboration: 02 Organisation: 10 Ethics: 12 Problem Solving: 08 Engagement: 16 your Ethereum address password to private key Signing this transaction will transfer stated Reputation Tokens + ETH gas payment from your account. Estimated gas cost is 0.02 ETH. Maximum gas cost is set to 0.05 ETH Transfer Reputation Tokens Left: 68 number of tokens to transfer Assign Reputation Signed TX Reputation Attribute token Balances Tokens left to assign Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 8. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 9. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 10. Block no: 45566778 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 11. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 12. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 13. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 14. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 15. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 16. Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
- 17. How do we… • …find Michelle’s transfers to everyone? • ...summarise reputation transferred by groups of users? • ...link data to semantically related external sources?
- 18. Linked Data indexing • Problems – Related data spread across blocks – No high-level semantics for contracts • Need – An index onto blockchain – To connect blockchain data to Linked Data – To allow richer contract semantics • LD index for blockchain
- 20. Flex Ledger 1.0 • A flexible format and protocol for decentralized ledgers on the Web • FL Web API to wrap blockchains – Vocab. extractable from JSON-LD model • No explicit semantics https://w3c.github.io/flex-ledger/
- 21. EthOn - An Ethereum Ontology http://ethon.consensys.net/EthOn_spec.html
- 24. Architecture
- 25. RDF Store Blockchain index Ethereum Listener Compiled Contract LOD Cloud Architecture Smart Contract Developer Linking Open Data cloud diagram 2017, by Andrejs Abele, John P. McCrae, Paul Buitelaar, Anja Jentzsch and Richard Cyganiak. http://lod-cloud.net/ Ethereum Node New Block Transaction & Block Metadata as RDF Deployment Contract Metadata as RDF
- 26. RDF Examples
- 31. SPARQL Example • Total value transferred to a specific contract address • Results
- 32. Smart Contracts
- 33. Indexing smart contracts • Contract deployment (Ethereum) – Blockchain address – Application Binary Interface (ABI) JSON • Exposed methods & parameters • Contract inaccessible without ABI – “Private” deployed contracts can’t be indexed
- 34. Smart Contract ABI JSON
- 36. Challenges & Future Work • Addressing – Linked Data needs URIs; how to get the “U”? • Ethereum Name Service: – “DNS for Ethereum” hosts .eth top-level domain – But specific to Ethereum • Currently use node URI – not distributed
- 37. Challenges & Future Work • Distributed index – Index on one node: centralised • But good for app-specific customisation • Could we have – Data (e.g., RDF) stored on IPFS/Swarm? – Queries executed within a smart contract? – i.e., both data & querying distributed • Performance & cost? • Use cases?
- 38. Our private Ethereum network • 6 nodes – 5 mining – 1 observation (running listener & RDF store) • Chain created 28th of April 2016 • 1 465 104 blocks (3.5 Gb) – As of 31/03/2017 • 22 million triples
- 39. Summary • Blockchains – Are a linked list based on hashes – No inbuilt indexing mechanism – Contain ‘smart contracts’ • Basic semantic indexing based on BLONDiE • Challenges – Universal naming system – Distributed vs centralised index
Editor's Notes
- #21: Not really clear why EthOn was started in preference to BLONDiE’s own Ethereum vocabulary
- #22: The EthOn Ethereum ontology, described using W3C RDF Schema and the Web Ontology Language. It is closely aligned with Gavin Wood's Ethereum yellow paper.
- #35: Generated by during compilation for Ethereum. ABI needed because contract is compiled.