The Science of Etherpad

How does Operational Transform work?

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