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Decentralised Semantic Web @ International Semantic Web Research Summer School 2018

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This in depth tutorial, presented at the 2018 International Semantic Web Research Summer School (ISWS), looks at the possibilities for a decentralised semantic web focusing primarily on the relationship between blockchains and linked data. The first part of the talk is an extensive explanation of what blockchains are and how they are used. This is followed by links to ongoing decentralised linked data research including Tim Berners-Lee's SOLID and Ruben Verborgh's Linked Data Fragments.

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Decentralised Semantic Web @ International Semantic Web Research Summer School 2018

  1. 1. The Role of Blockchains in a Decentralised Semantic Web John Domingue (@johndmk) KMi, The Open University International Semantic Web Research Summer School 4th July 2018, Bertinoro
  2. 2. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Societal Data Issues
  3. 3. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 “We demonstrated that the Web had failed instead of served humanity, as it was supposed to have done, and failed in many places,” he told me. The increasing centralization of the Web, he says, has “ended up producing—with no deliberate action of the people who designed the platform—a large-scale emergent phenomenon which is anti-human.”
  4. 4. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Google Data https://www.theguardian.com/commentisfree/2018/mar/28/all-the-data-facebook-google-has-on-you-privacy • 5.5 GB • Everywhere you’ve been • Everything you’ve ever searched (and deleted) • Advertisement profile • All the apps you use • All your YouTube history
  5. 5. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Thin Files and Data Poor 5
  6. 6. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 2 Billion Unbanked
  7. 7. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 The Windrush Scandal 7http://www.theweek.co.uk/92944/who-are-the-windrush-generation-and-why-are-they-facing-deportation
  8. 8. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Claim 8
  9. 9. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Proof 9
  10. 10. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Attestation 1 0
  11. 11. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Data Changes 1 1
  12. 12. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Fake Data 1 2
  13. 13. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Centralised Data 1 3
  14. 14. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Toxic Data 1 4
  15. 15. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Jurisdictional Politics 1 5
  16. 16. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Monopolistic Tendencies 1 6
  17. 17. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Self Sovereign Identity 1 7
  18. 18. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Verifiable Claims WG
  19. 19. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Blockchain Impact
  20. 20. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Blockchain World Economic Forum Survey Projects Blockchain ‘Tipping Point’ by 2023 Santander: Blockchain Tech Can Save Banks $20 Billion a Year
  21. 21. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Everledger www.everledger.io
  22. 22. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 IBM: Device Democracy
  23. 23. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Blockchain Overview
  24. 24. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Ledgers
  25. 25. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Cryptographic Hash Function https://en.wikipedia.org/wiki/Cryptographic_hash_function
  26. 26. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Immutable Linked List
  27. 27. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Immutable Linked List
  28. 28. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Blockchain Consensus Mechanisms
  29. 29. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Proof of Work Hard to outpace the entire rest of the network… a 51% attack could do it, but otherwise it is like buying thousands of lottery tickets – doesn’t help you that much! Source: Marc Eisenstadt ‘What is the genius behind Bitcoin’
  30. 30. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Proof of Work Find x such that f(nonce + x) < t (cryptographic hash) "Hello, world!0" => 1312af178c253f84028d480a6adc1e25e81caa44c749ec81976192e2ec934c64 "Hello, world!1" => e9afc424b79e4f6ab42d99c81156d3a17228d6e1eef4139be78e948a9332a7d8 "Hello, world!2" => ae37343a357a8297591625e7134cbea22f5928be8ca2a32aa475cf05fd4266b7 ... "Hello, world!4248" => 6e110d98b388e77e9c6f042ac6b497cec46660deef75a55ebc7cfdf65cc0b965 "Hello, world!4249" => c004190b822f1669cac8dc37e761cb73652e7832fb814565702245cf26ebb9e6 "Hello, world!4250" => 0000c3af42fc31103f1fdc0151fa747ff87349a4714df7cc52ea464e12dcd4e9
  31. 31. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 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.
  32. 32. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 BitCoin Mining http://knkx.org/post/central-wash-home-nations-biggest-bitcoin-mine-more-coming
  33. 33. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Consensus Mechanisms (1/6)
  34. 34. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Consensus Mechanisms (2/6)
  35. 35. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Consensus Mechanisms (3/6)
  36. 36. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Consensus Mechanisms (4/6)
  37. 37. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Consensus Mechanisms (5/6)
  38. 38. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Consensus Mechanisms (6/6)
  39. 39. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Ethereum
  40. 40. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Ethereum Virtual Machine The Ethereum Virtual Machine can be thought of as a large decentralized computer containing millions of objects, called "accounts", which have the ability to maintain an internal database, execute code and talk to each other. There are 2 types of Accounts: Externally owned account (EOA): an account controlled by a private key that has the ability to send ether and messages from it. ‘Smart’ Contract: an account that has its own code, and is controlled by code. Any user can trigger an action by sending a transaction from an EOA, setting Ethereum's wheels in motion. If the destination of the transaction is another EOA, then the transaction may transfer some ether but otherwise does nothing However, if the destination is a ‘Smart’ Contract, then the contract in turn activates, and automatically runs its code. Sources: Ethereum Development Tutorial
  41. 41. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Ethereum External Accounts http://ethdocs.org/en/latest/account-management.html Every account is defined by a pair of keys, a private key and public key A keyfile holds encoded key pair data as JSON with the private key encrypted with a user given password Accounts are indexed by their address which is derived from the public key by taking the last 20 bytes Accounts use public key cryptography to sign transaction.
  42. 42. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Ethereum External Accounts http://ethdocs.org/en/latest/account-management.html Server side external Accounts Client side external Accounts Client side keyfiles are held in a keystore managed by wallet Software running either in a browser or on the client computer Server side account keyfiles are held in the keystore folder where your Ethereum node data is located
  43. 43. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 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/
  44. 44. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 DApps A Đapp is a decentralised application which serves some specific purpose to its users, but which has the important property that the application itself does not depend on any specific party existing. Rather than serving as a front-end for selling or providing a specific party's services, a Đapp is a tool for people and organizations on different sides of an interaction use to come together without any centralized intermediary. A Dapp consists of two parts: a frontend, written in HTML or QML, and a backend (think of it as the ‘database’ for your frontend).
  45. 45. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 DBrowsers It is an end user interface onto the Ethereum blockchain. A DBrowser is how users will find and interact with DApps ‘Mist’ is the name of the Ethereum DBrowser.
  46. 46. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 DAOs and ICOs
  47. 47. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Distributed Autonomous Organisation
  48. 48. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  49. 49. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  50. 50. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  51. 51. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  52. 52. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  53. 53. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  54. 54. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  55. 55. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Initial Public Offering
  56. 56. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Characteristics of Blockchain DApps • Shared database • Multiple writers • Absence of trust • Disintermediation • Transaction interaction • Set rules • Validators • Asset backing http://www.multichain.com/blog/2015/11/avoiding-pointless-blockchain-project/
  57. 57. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Validity and Blockchains • Hashing secures blockchain and for any data • Immutability • Consensus mechanism enforces ‘house rules’ • Every peer has a copy of the data • Smart contracts enforce agreements • Assets transferred on agreement • Inbuilt punishment mechanism
  58. 58. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Blockchain Use Cases in Higher Education
  59. 59. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 MSc Certificates on Blockchain http://digitalcurrency.unic.ac.cy/certificates
  60. 60. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 MSc Certificates on Blockchain
  61. 61. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Learning Machine
  62. 62. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 For example, after taking an examination to demonstrate his or her academic proficiency level, an individual could direct the testing organization to share the test results with one or more third-party evaluating organizations. With this diversification and the changes it brings about, different evaluating organizations may come to utilize individuals' test results in different ways, each in accordance with its own evaluation methods. http://www.sony.net/SonyInfo/News/Press/201602/16-0222E/index.html Sony Global
  63. 63. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 MSc Certificates on Blockchain
  64. 64. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 https://www.appii.io/ Collaboration with APPII
  65. 65. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Badges on the Blockchain
  66. 66. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Demos of movies available at: http://blockchain.open.ac.uk/ Peer Reputation and Badging
  67. 67. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin 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: Problem Solving: 10 Engagement: 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
  68. 68. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  69. 69. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  70. 70. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Block no: 45566778 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  71. 71. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  72. 72. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  73. 73. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  74. 74. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  75. 75. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  76. 76. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Michelle transfers 4 Reputation tokens for ‘Organisation’ to Kevin
  77. 77. Blockchains and Decentralised Semantic Web Pill John Domingue (@johndmk), Michelle Bachler, Allan Third and Ruben Verborgh KMi, The Open University and imec, Ghent University International Semantic Web Research Summer School 4th July 2018, Bertinoro
  78. 78. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Solid https://solid.mit.edu/ https://rubenverborgh.github.io/ISWS2018/
  79. 79. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Decentralized web apps share access to data stores
  80. 80. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Different app and storage providers compete independently
  81. 81. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Connecting blockchain and Linked Data https://rubenverborgh.github.io/ISWS2018/
  82. 82. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018
  83. 83. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 EthOn - An Ethereum Ontology http://ethon.consensys.net/EthOn_spec.html
  84. 84. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 BLONDiE https://github.com/hedugaro/Blondie
  85. 85. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Possible Linked Data Interfaces exist between two Extremes
  86. 86. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Linked Data Fragments is a uniform view on LD interfaces
  87. 87. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Linked Data Fragments is a uniform view on LD interfaces Every Linked Data Interface offers specific fragments of a Linked Data set
  88. 88. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Linked Data Fragment • Data • Metadata • Controls
  89. 89. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Linked Data Fragment • Data – what triples does the fragment contain? • Metadata • Controls
  90. 90. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Linked Data Fragment • Data – what triples does the fragment contain? • Metadata – do we know more about the data/fragment? • Controls
  91. 91. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Linked Data Fragment • Data – what triples does the fragment contain? • Metadata – do we know more about the data/fragment? • Controls – how can we access more data?
  92. 92. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Data Dump • Data – all dataset triples • Metadata – number of triples, file size • Controls – none
  93. 93. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • SPARQL Query Result • Data – triples matching query • Metadata – none • Controls - none
  94. 94. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Linked Data Document • Data – triples about a topic • Metadata – creator, maintainer • Controls – links to other Linked Data documents
  95. 95. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Each type of Linked Data Fragment is defined by three characteristics • Triple Pattern Fragrment • Data – matches of triple pattern • Metadata – total number of matches • Controls – access to all other Triple Pattern Fragments of the same dataset
  96. 96. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Linked Data Fragments 1 0 1
  97. 97. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Linked Data Fragments 1 0 2
  98. 98. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Interplanetary File System (IPFS) • Content-addressed distributed storage (CADS) • Files identified by hash of contents • Shared across BitTorrent-based network
  99. 99. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Decentralised Linked Data on Blockchains • Guarantees of immutability • Data cannot be changed once published • Integrity of valuable data • Financial • Medical • Political/politically-sensitive e.g., climate science data • Academic Publishing
  100. 100. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Dimensions of Decentralisation for Linked Data • Decentralised • Data storage • Querying • Verification • Other criteria • Storage costs • Query costs • Level of integrity guarantee
  101. 101. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Decentralising Linked Data Storage & Querying • Identified 5 approaches • CADS • CADS + distributed ledger • Standard LOD + distributed ledger verifier • Standard LOD + distributed ledger backend • “Pure” distributed ledger • Compared with base case of standard LOD • SPARQL/Linked Data Fragments querying
  102. 102. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Base case Centralised storage and querying No verification Query = Linked Data Fragments
  103. 103. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 CADS
  104. 104. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 CADS • Data decentralised (copy-on-demand) • Queries centralised • Verification • Centralised (central source of IPFS hash) • Weak (need to trust source of IPFS hash) • Need to re-compute hash over entire data set • No timestamping
  105. 105. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 CADS + Distributed Ledger
  106. 106. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 CADS + DL Data decentralised But copy-on-demand Queries centralised Verification Decentralised (blockchain source of IPFS hash) Strong (IPFS hash immutable, signable) Need to re-compute hash over entire data set Timestamping
  107. 107. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Base case + DL Verifier Centralised storage and querying Verify query results with copy of original data on blockchain
  108. 108. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Base case + DL Backend
  109. 109. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Base case + DL Backend Semi-decentralised queries - any node can be a query frontend Decentralised data verified directly from blockchain
  110. 110. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 “Pure” Distributed Ledger Decentralised storage and querying Data comes directly from blockchain
  111. 111. John Domingue, Role of Blockchains in a Decentralised Semantic Web, 4th July, ISWS 2018 Summary
  112. 112. THANK YOU FOR YOUR ATTENTION! Questions? @johndmk · john.domingue@open.ac.uk· SlideShare: johndomingue

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