Resource Oriented Architectures

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Resource Oriented Architectures

  1. 1. REST and Resource Oriented Architectures Gabriele Lana gabriele.lana@gmail.com
  2. 2. what is REST?
  3. 3. REST is not a Protocol an Architecture a Software a Standard a fancy name for Web Services a Buzzword
  4. 4. Representational State Transfer Roy T. Fielding “Architectural Styles and the Design of Network-based Software Architectures” Ph.D dissertation, 2000
  5. 5. REST is a Software Architecture Style a set of Constraints on Component Interaction that, when obeyed, cause the resulting Architecture to have certain properties Roy T. Fielding http://roy.gbiv.com/untangled/2008/on-software-architecture
  6. 6. ?
  7. 7. prediction for 2009 “Roy Fielding will officially disown most of the RESTful authors and software packages available. Nobody will care, or worse, somebody looking to make a name for themselves will proclaim that “Roy doesn't really understand REST”, and they'll be right: Roy doesn't understand what they consider to be REST” http://dotnet.dzone.com/articles/ted-neward-2009-predictions-20
  8. 8. why? “... the motivation for developing REST was to create an architectural model for how the Web should work, such that it could serve as the guiding framework for the Web protocol standards” http://www.ics.uci.edu/~fielding/pubs/dissertation/evaluation.htm
  9. 9. no Silver Bullets REST vs SOA vs SOAP vs RPC vs WS-* vs ...
  10. 10. but sometimes REST is better :-)
  11. 11. web applications Information Flow RDB HTTP OOP MS
  12. 12. HTTP is REST RDB HTTP OOP MS
  13. 13. Impedance Mismatch RDB HTTP OOP MS
  14. 14. Accidental Complexity RDB HTTP OOP MS
  15. 15. Essential Complexity RDB HTTP OOP MS
  16. 16. RDB RPC OOP MS HTTP RPC
  17. 17. Resource Oriented Architectures RDB HTTP ROA MS
  18. 18. maybe not today, but Yes, we Can HTTP ROA DATA
  19. 19. REST by Example (Chess)
  20. 20. how to Design a RESTful service Step by Step Leonard Richardson & Sam Ruby “RESTful Web Services”, O’Reilly 2007
  21. 21. 1. every Resource must be Identified
  22. 22. Pawn Move Bishop Game Player Rank Board Rook File Knight Position Queen Square
  23. 23. every Concept in your Domain can be a Resource
  24. 24. 2. design the URIs (Ubiquitous Language)
  25. 25. /position/wqd3,wkd1,bqd7,bkd8
  26. 26. /position/wqd3,wkd1,bqe6,bkf8/d3-d8
  27. 27. /move/wqd3,wkd1,bkf8-wqd8,wkd1,bkf8
  28. 28. /position/initial
  29. 29. /board/4815162342 /position/wqd3,wkd1,bqe6,bkf8 move = d3-d8 /position/wqd8,wkd1,bqe6,bkf8
  30. 30. /player/50298
  31. 31. 3. for each Resource expose a subset of the Uniform Interface
  32. 32. Uniform Interface GET (Read) POST (Create) PUT (Update) DELETE (Delete)
  33. 33. GET /player/50298 HTTP/1.1 Retrieve informations on identified Resource Idempotent, should not change the Resource State
  34. 34. POST /position/wqd3,wkd1,bke8 HTTP/1.1 n move = d3-d8 HTTP/1.1 302 Found Location: /position/wqd8,wkd1,bke8 POST to let Resources process informations
  35. 35. POST /game HTTP/1.1 n white = /player/50298 & black = /player/39650 HTTP/1.1 201 Created Location: /game/42 POST to Create new Resources
  36. 36. PUT /board/4815162342 HTTP/1.1 n position = /position/wqd3,wkd2,bke8 HTTP/1.1 205 Reset Content PUT to Update Resource Informations
  37. 37. PUT /position/wqd3,wkd1,bke8 HTTP/1.1 n position = /position/wqd3,wkd2,bke8 HTTP/1.1 405 Method Not Allowed a Method can be not supported by a Resource but should not be ignored
  38. 38. DELETE /board/4815162342 HTTP/1.1 HTTP/1.1 204 No Content DELETE to logically Remove Resources
  39. 39. 4. for each Resource design Representations from and to Client
  40. 40. GET /position/wqd3,wkd2,bke8 HTTP/1.1 Accept: text/plain HTTP/1.1 200 OK Content-Type: text/plain;format=fen n 3k4/8/3q4/8/8/8/8/5K2 client/server Content Negotiation (MIME properties)
  41. 41. GET /position/wqd3,wkd2,bke8 HTTP/1.1 Accept: image/png;q=0.8, text/plain;q=0.2 HTTP/1.1 200 OK Content-Type: image/png n PNG... client/server Content Negotiation (Preferences)
  42. 42. GET /position/wqd3,wkd2,bke8.png HTTP/1.1 Accept: image/png HTTP/1.1 200 OK Content-Type: image/png n PNG... client Explicit Request of Content-Type
  43. 43. GET /position/wqd3,wkd2,bke8.gif HTTP/1.1 Accept: image/gif HTTP/1.1 406 Not Acceptable or more friendly HTTP/1.1 300 Multiple Choices Content-Type: application/xml n <choices><content type=”image/png” uri=”...”>
  44. 44. GET /game/42 HTTP/1.1 Accept: application/vnd.dharma.chess <game> <player role=”white”>/player/1001</player> <player role=”black”>/player/1002</player> <moves> <position>/position/initial</position> </moves> </game> custom Content-Type
  45. 45. wait... what about plain old Web Applications?
  46. 46. GET /game/42 HTTP/1.1 Accept: application/xhtml+xml <html> ... <a rel=”owner” href=”/player/1001”>...</a> ... <ul class=”moves”> <li><image src=”/position/initial.png”/></li> </ul> </html> Semantic Web is not a dream
  47. 47. Tim Berners-Lee on Linked Data “... almost 20 years ago I wanted to reframe the way we use informations ... I invented the Word Wide Web ... now is time for a new reframing...” Tim Berners-Lee @ http://linkeddata.org
  48. 48. expected behavior of the web 1. Use URIs as names for things 2. Use HTTP URIs so that people can look up those names 3. When someone looks up a URI, provide useful information 4. Include links to other URIs, so that they can discover more things
  49. 49. POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic dXN1cm5hbWU6cG... n <game> <player>...</player> <moves> <position>/position/initial</position> <position color=”white”> /position/wra1,wna2,...,wpd4,... </position> </moves> </game> ... from and to the Client
  50. 50. 5. design typical flows and error conditions
  51. 51. POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic dXN1... n <game> <player>...</player> <moves> <position>/position/initial</position> <position color=”white”> /position/wra1,wna2,...,wpd4,... </position> </moves> </game> white Player make first move
  52. 52. HTTP/1.1 201 Created Location: /game/42/position/2 Response to the white Player GET /game/42/position/2 HTTP/1.1 301 Moved Permanently Location: /position/wra1,wna2,...,wpd4,...
  53. 53. GET /game/42 HTTP/1.1 Authorization: Basic dXN1... n <game> <player>...</player> <moves>...</player> </game> GET /game/42 HTTP/1.1 Authorization: Basic aYR5... n <game> <player>...</player> <moves>...</player> </game> both Players must GET the game Representation
  54. 54. POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic aYR5... n <game> <player>...</player> <moves> <position>/position/initial</position> <position>/position/wra1,wna2,...,wpd4,...</position> <position color=”black”> /position/wra1,wna2,...,bpd5,... </position> </moves> </game> black Player can make next move
  55. 55. POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic aYR5... n ... what if black Player try to resend? HTTP/1.1 409 Conflict the game Representation is out of date
  56. 56. POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic aYR5... n ... what if black Player try to move again? HTTP/1.1 403 Forbidden the black Player should wait for the white Player to move
  57. 57. POST /position/wqd3,wkd1,bke8 HTTP/1.1 n move = d3-e8 what if we try to make a wrong move? HTTP/1.1 404 Not Found Business Rules could be easily expressed through the Resource's Behavior
  58. 58. wait... what about complex User Interfaces?
  59. 59. what about Gmail
  60. 60. what about Gmail JS HTTP ? JS
  61. 61. what about Gmail
  62. 62. FAQ: cool URIs are RESTful? OpenSocial /people/{guid}/@all Collection of all people connected to user {guid} http://www.opensocial.org/Technical-Resources/opensocial-spec-v081/restful-protocol.html
  63. 63. FAQ: REST is stateless? Statelessness says that all possible states of the server are also Resources (Resource State)
  64. 64. FAQ: REST is stateless? Statelessness says that each message contains all the informations necessary to understand the Request (Application State)
  65. 65. Representational State Transfer Application State R3 R4 R2 R1 CLIENT SERVER Resource State
  66. 66. your application can be Discoverable
  67. 67. your application can be Testable
  68. 68. Testability View Model Control HTTP
  69. 69. Testability too much code untested View Model Control HTTP
  70. 70. Testability too fragile and unreliable View Model Control HTTP
  71. 71. Testability Player Board Position Game Move Js HTTP
  72. 72. Testability what about the view? Player Board Position Game Move Js HTTP
  73. 73. your application can be Composable
  74. 74. your application can be Scalable
  75. 75. ...so what Really means (for me) being RESTful?
  76. 76. now the Web can talk about chess

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