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The Science of Etherpad

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Avatar for Tim Cameron Ryan Tim Cameron Ryan
May 14, 2012
Programming
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The Science of Etherpad

How does Operational Transform work?

Avatar for Tim Cameron Ryan

Tim Cameron Ryan

May 14, 2012
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Transcript

  1. THE SCIENCE OF ETHERPAD MAKING ANY DOCUMENT COLLABORATIVE, ANYWHERE

  2. Operations

  3. app

  4. apple

  5. “app” + ”le”

  6. app Operation 1 1.  insertCharacter “a” 2.  insertCharacter “p” 3. 

    insertCharacter “p“

  7. apple Operation 2 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  insertCharacter “l” 5.  insertCharacter “e“

  8. applecore Operation 2 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  retain (skip character) 5.  retain (skip character) 6.  insertCharacter “c” 7.  insertCharacter “o“ 8.  insertCharacter “r“ 9.  insertCharacter “e“

  9. Composition

  10. appl Operation 1 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  insertCharacter “l” apple Operation 2 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  retain (skip character) 5.  insertCharacter “e”

  11. Operation 1+2 1.  retain (skip character) 2.  retain (skip character)

    3.  retain (skip character) 4.  insertCharacter “l” 5.  insertCharacter “e“ appl apple

  12. Concurrency

  13. app app CLIENT A CLIENT B

  14. appl appe CLIENT A CLIENT B

  15. appl Operation A 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  insertCharacter “l” appe Operation B 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “e” CLIENT A CLIENT B

  16. appl Operation B 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  insertCharacter “e” appe Operation A 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “l” CLIENT A CLIENT B

  17. appel Operation B 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  insertCharacter “e” apple Operation A 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “l” CLIENT A CLIENT B

  18. appel apple CLIENT A CLIENT B

  19. Operational Transform

  20. “A theoretical framework of concurrency control” that “provides a mechanism

    for sanely resolving [editing] conflicts so that neither user intervention or locking become necessary.” A mechanism to “transform” two operations in conflict, resulting in two new operations which bring both clients into a common state.

  21. app app CLIENT A CLIENT B SERVER

  22. appl Operation A 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  insertCharacter “l” CLIENT A SERVER 1 appe Operation B 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “e” CLIENT B 2

  23. Operation A 1.  retain (skip character) 2.  retain (skip character)

    3.  retain (skip character) 4.  insertCharacter “l” SERVER TRANSFORM Operation B 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “e” Operation B` 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  retain (skip character) 5.  insertCharacter “e” Operation A` 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “l” 5.  retain (skip character)

  24. appl Operation B` 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  retain (skip character) 5.  insertCharacter “e” CLIENT A SERVER appe Operation A` 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “l” 5.  retain (skip character) CLIENT B B` A`

  25. apple Operation B` 1.  retain (skip character) 2.  retain (skip

    character) 3.  retain (skip character) 4.  retain (skip character) 5.  insertCharacter “e” CLIENT A SERVER apple Operation A` 1.  retain (skip character) 2.  retain (skip character) 3.  retain (skip character) 4.  insertCharacter “l” 5.  retain (skip character) CLIENT B B` A`

  26. apple apple CLIENT A CLIENT B

  27. CLIENT A CLIENT B A1: retain 3, insert “l” Broadcast

    A1 Apply A1` SERVER

  28. CLIENT A CLIENT B SERVER A1: retain 3, insert “l”

    B1: retain 3, insert “e” Transform A1 x B1 Apply A1` Apply B1`

  29. CLIENT A CLIENT B SERVER A1: retain 3, insert “l”

    B1: retain 3, insert “e” A2: retain 4, insert “core” Transform A1 x B1 Apply A1` Transform A2 x B1` Apply B1`` Broadcast A2 Apply A2`

  30. CLIENT A CLIENT B SERVER A1: retain 3, insert “l”

    B1: retain 3, insert “e” A2: retain 4, insert “core” Transform A1 x B1 B2: retain 4, insert “sauce” Transform B2 x A1` Apply A1`` Transform A2 x B1` Apply B1`` Transform A2` x B2` Apply A2`` Apply B2``

  31. CLIENT A CLIENT B SERVER A1: retain 3, insert “l”

    B1: retain 3, insert “e” A2: retain 4, insert “core” Transform A1 x B1 B2: retain 4, insert “sauce” Transform B2 x A1` Apply A1`` Transform A2 x B1` Apply B1`` Transform A2` x B2` Apply A2`` Apply B2``

  32. Markup

  33. big apple

  34. big apple

  35. <i>big</i> <b>apple</b>

  36. <i>big</i> <b>apple</b>

  37. <i>big</i> <b>apple</b> Operation 1.  insertStartTag “i” 2.  insertCharacter “b” 3. 

    insertCharacter “i” 4.  insertCharacter “g” 5.  insertEndTag “i” 6.  insertCharacter “ ” 7.  insertStartTag “b” 8.  insertCharacter “a” 9.  insertCharacter “p” 10.  insertCharacter “p” 11.  insertCharacter “l” 12.  insertCharacter “e” 13.  insertEndTag “b”

  38. a big word a big word CLIENT A CLIENT B

  39. a <b>big</b> word Operation A 1.  retain 2 2.  insertStartTag

    “b” 3.  retain 3 4.  insertEndTag “b” a biiiiig word Operation B 1.  retain 3 2.  insertCharacters “iiii” CLIENT A CLIENT B

  40. a <b>big</b> word Operation B` 1.  retain 4 2.  insertCharacters

    “iiii” a biiiiig word Operation A` 1.  retain 2 2.  insertStartTag “b” 3.  retain 5 4.  insertEndTag “b” CLIENT A CLIENT B

  41. a <b>biiiiig</b> word Operation B` 1.  retain 4 2.  insertCharacters

    “iiii” a <b>biiiiig</b> word Operation A` 1.  retain 2 2.  insertStartTag “b” 3.  retain 5 4.  insertEndTag “b” CLIENT A CLIENT B

  42. Preserving Intent

  43. CLIENT A CLIENT B Desired Word1 Word2 Word3 <ol> <li>

    Word4 Word5 Word6 </li> </ol> <ol> <li> Word1 Word2 Word3 Word4 </li> </ol> Word5 Word6 <ol> <li> Word1 Word2 Word3 Word4 Word5 Word6 </li> </ol>

  44. CLIENT A CLIENT B Desired Word1 Word2 <p> Word3 Word4

    Word5 Word6 </p> <h1> Word1 Word2 Word3 Word4 </h1> Word5 Word6 <h1> Word1 Word2 </h1> <p> Word3 Word4 </p> <p> Word5 Word6 </p>

  45. CLIENT A CLIENT B Desired Word1 Word2 Word3 <i> Word4

    Word5 Word6 Word7 Word8 </i> <b> Word1 Word2 Word3 Word4 Word5 </b> Word6 Word7 Word8 <b> Word1 Word2 Word3 </b> <bi> Word4 Word5 </bi> <i> Word6 Word7 Word8 </i>

  46. •  retain •  deleteCharacter •  deleteStartTag(tag, attrs) •  deleteEndTag() • 

    deleteEmptyTag() •  insertCharacter •  insertStartTag(tag, attrs) •  insertEndTag() •  insertEmptyTag() •  modifyAttrs(attrs) Deletion Phase Insertion Phase OPERATION ATOMS

  47. Containers like: preserve unlike: priority Blocks like: priority unlike: priority

    Styles like: preserve unlike: merge Inline <ul> <li> <ol> <blockquote> <p> <div> <h1> <h2> <h3> <pre> <b> <i> <span> <u> <s> “text” <br> DOCUMENT SCHEMA