Since 2003, the Atom format has been used as yet another feed format like RSS, but the Atom protocol opens the door to far more uses of Atom as both a means for distribution and publication. Ben Ramsey introduces the Atom format and protocol, explaining how these can form the foundation of any publishing service and serve as a platform for rich Internet applications.

1. Introduction to AtomPub Web Services
Ben Ramsey • International PHP Conference • 11 Oct 2010

2. Hi, I’m Ben.
‣ VP of Engineering at Moontoast
‣ Co-founder and organizer emeritus of the Atlanta PHP user group
‣ Current organizer of the Nashville PHP user group
‣ I blog at benramsey.com
‣ I tweet at @ramsey
‣ Please rate this presentation: http://joind.in/2185
Introduction to AtomPub Web Services • Ben Ramsey 2

3. Atom & AtomPub?

4. What’s the difference?

5. Atom: RFC 4287
Introduction to AtomPub Web Services • Ben Ramsey 5

6. Atom is an XML-based document format that
describes lists of related information known as
“feeds”. Feeds are composed of a number of items,
known as “entries”, each with an extensible set of
attached metadata. For example, each entry has a
title.
The primary use case that Atom addresses is the
syndication of Web content such as weblogs and
news headlines to Web sites as well as directly to
user agents.
—RFC 4287, §1

7. Atom is an XML language.

8. AtomPub: RFC 5023
Introduction to AtomPub Web Services • Ben Ramsey 8

9. The Atom Publishing Protocol is an application-level
protocol for publishing and editing Web Resources using
HTTP and XML 1.0. The protocol supports the creation of
Web Resources and provides facilities for:
Collections: Sets of Resources, which can be retrieved in
whole or in part.
Services: Discovery and description of Collections.
Editing: Creating, editing, and deleting Resources.
The Atom Publishing Protocol is different from many
contemporary protocols in that the server is given wide
latitude in processing requests from clients.
—RFC 5023, §1

10. AtomPub is a
publishing protocol.

11. What about RSS?
Introduction to AtomPub Web Services • Ben Ramsey 11

12. Content Types
‣ RSS allows only for plain text and escaped HTML content types
‣ Atom provides for plain text, escaped HTML, XHTML, XML, and
Base64-encoded binary data
Introduction to AtomPub Web Services • Ben Ramsey 12

13. Internationalization
‣ RSS may have a language set for a feed, but doesn’t have a way to
indicate language for items in the feed
‣ Atom uses the xml:lang attribute to specify language on a per-element
basis
‣ Atom uses IRIs, which allow the usage of characters in identifiers
outside of ASCII
Introduction to AtomPub Web Services • Ben Ramsey 13

14. Modularity
‣ RSS vocabulary elements aren’t reusable in other XML vocabularies
‣ Atom was designed to allow its vocabulary to be mixed with other XML
vocabularies
‣ Namespaces! Atom has one; RSS does not
Introduction to AtomPub Web Services • Ben Ramsey 14

15. Other Things
‣ RSS has no schema; Atom has a RelaxNG schema
‣ RSS defines no mechanism for handling relative URIs; Atom uses
xml:base
‣ Various implementations in RSS leads to interoperability problems
‣ No standard protocol for publishing; RSS is read only
Introduction to AtomPub Web Services • Ben Ramsey 15

16. Atom was created to solve
the RSS problems.

17. Profile of Atom
‣ Atom Syndication Format
‣ An XML-based web content and metadata syndication format
‣ Defined by IETF RFC 4287
‣ Fixes the “problems” of RSS
‣ XML namespace: http://www.w3.org/2005/Atom
Introduction to AtomPub Web Services • Ben Ramsey 17

18. Profile of AtomPub
‣ Atom Publishing Protocol or APP
‣ A protocol for publishing and editing web resources using HTTP and
XML
‣ Defined by IETF RFC 5023
‣ Uses Atom as it’s XML syntax
‣ XML namespace: http://www.w3.org/2007/app
Introduction to AtomPub Web Services • Ben Ramsey 18

19. Basics of AtomPub
‣ Each resource has a unique identifier
‣ The resources are well-connected
‣ Resources share the same interface
‣ There is no state; requests are atomic
‣ Follows a resource-oriented architecture
Introduction to AtomPub Web Services • Ben Ramsey 19

20. Terminology
‣ Entry
‣ Feed/Collection
‣ Category Document
‣ Service Document
Introduction to AtomPub Web Services • Ben Ramsey 20

21. Content Types
‣ Entry:
application/atom+xml;type=entry
‣ Feed/Collection:
application/atom+xml
‣ Category Document:
application/atomcat+xml
‣ Service Document:
application/atomsvc+xml
Introduction to AtomPub Web Services • Ben Ramsey 21

22. Designing an AtomPub Service
Introduction to AtomPub Web Services • Ben Ramsey 22

23. What will our service do?
‣ Expose users
‣ Expose content
‣ Allow users to manipulate content
Introduction to AtomPub Web Services • Ben Ramsey 23

24. Step 1:
Define our URIs

25. Users
‣ /user
‣ /user/{username}
‣ For example: /user/ramsey
Introduction to AtomPub Web Services • Ben Ramsey 25

26. Content
‣ /content
‣ /content/{id}
‣ For example: /content/1234
Introduction to AtomPub Web Services • Ben Ramsey 26

27. Step 2:
Define the relationships

28. Relationship Building
‣ user ⇛ content:
one to many
‣ content ⇛ user:
one to one
Introduction to AtomPub Web Services • Ben Ramsey 28

29. Step 3:
Define the interface

30. Methods Cut & Paste
GET Copy
PUT Paste Over
POST Paste After
DELETE Cut

31. Actions for User Resources
‣ Retrieve user collection:
GET /user
‣ Create a new user:
POST /user
‣ Modify an existing user:
PUT /user/ramsey
‣ Delete a user:
DELETE /user/ramsey
Introduction to AtomPub Web Services • Ben Ramsey 31

32. Actions for Content Resources
‣ Retrieve content:
GET /content
‣ Create new content:
POST /content
‣ Modify content:
PUT /content/1234
‣ Remove content:
DELETE /content/1234
Introduction to AtomPub Web Services • Ben Ramsey 32

33. Other Actions
‣ Service discovery:
GET /
‣ Retrieve content for a particular user:
GET /user/ramsey/content
Introduction to AtomPub Web Services • Ben Ramsey 33

34. Let’s see it in action
Introduction to AtomPub Web Services • Ben Ramsey 34

35. GET / HTTP/1.1
Host: atom.example.org
HTTP/1.x 200 OK
Date: Mon, 21 Sep 2009 16:33:45 GMT
Content-Type: application/atomsvc+xml

36. <?xml version="1.0" encoding="utf-8"?>
<service xmlns="http://www.w3.org/2007/app"
xmlns:atom="http://www.w3.org/2005/Atom"
xml:base="http://atom.example.org/">
<workspace>
<atom:title>Our Content Store</atom:title>
<collection href="user">
<atom:title>Users</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories href="cat/user"/>
</collection>
<collection href="content">
<atom:title>Content</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories href="cat/content"/>
</collection>
</workspace>
</service>

37. GET /user HTTP/1.1
Host: atom.example.org
HTTP/1.x 200 OK
Date: Mon, 21 Sep 2009 16:34:26 GMT
Content-Type: application/atom+xml

38. <?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
xmlns:app="http://www.w3.org/2007/app"
xml:base="http://atom.example.org/">
<title>Users</title>
<updated>2009-09-21T05:21:19Z</updated>
<id>tag:example.org,2009-09:user</id>
<app:collection href="user">
<title>Users</title>
<app:accept>application/atom+xml;type=entry</app:accept>
<app:categories href="cat/user"/>
</app:collection>
<link rel="first" href="user"/>
<link rel="last" href="user?p=23"/>
<link rel="next" href="user?p=2"/>
<entry>
...
</entry>
</feed>

39. Manipulating a User
Introduction to AtomPub Web Services • Ben Ramsey 39

40. GET /user/ramsey HTTP/1.1
Host: atom.example.org
HTTP/1.x 200 OK
Date: Mon, 21 Sep 2009 16:34:26 GMT
Content-Type: application/atom+xml;type=entry

41. <?xml version="1.0" encoding="utf-8"?>
<entry xmlns="http://www.w3.org/2005/Atom"
xml:base="http://atom.example.org/">
<title>ramsey</title>
<author>
<name>ramsey</name>
</author>
<link rel="self" href="user/ramsey"/>
<link rel="edit" type="application/atom+xml;type=entry"
href="user/ramsey"/>
<link rel="related" href="user/ramsey/content"/>
<id>tag:example.org,2008:user/ramsey</id>
<updated>2009-09-21T13:45:00Z</updated>
<published>2008-05-23T16:23:34Z</published>
<content type="xhtml">
<div class="vcard">
<a class="fn">Ben Ramsey</a>
<span class="tel">123-456-7890</span>
</div>
</content>
</entry>

42. Modify the Entry Locally
Introduction to AtomPub Web Services • Ben Ramsey 42

43. <?xml version="1.0" encoding="utf-8"?>
<entry xmlns="http://www.w3.org/2005/Atom"
xml:base="http://atom.example.org/">
<title>ramsey</title>
<author>
<name>ramsey</name>
</author>
<link rel="self" href="user/ramsey"/>
<link rel="edit" type="application/atom+xml;type=entry"
href="user/ramsey"/>
<link rel="related" href="user/ramsey/content"/>
<id>tag:example.org,2008:user/ramsey</id>
<updated>2009-09-22T09:14:58Z</updated>
<published>2008-05-23T16:23:34Z</published>
<content type="xhtml">
<div class="vcard">
<a class="fn url" href="http://benramsey.com/">Ben Ramsey</a>
<span class="org">Moontoast</span>
<span class="tel">123-456-7890</span>
</div>
</content>
</entry>

44. PUT /user/ramsey HTTP/1.1
Host: atom.example.org
Content-Type: application/atom+xml;type=entry
{body here}
HTTP/1.x 200 OK
Date: Mon, 22 Sep 2009 09:14:59 GMT
Content-Type: application/atom+xml;type=entry

45. Add Some Content
Introduction to AtomPub Web Services • Ben Ramsey 45

46. First, a Few Notes
‣ You need authentication!
‣ Perhaps you need encryption
‣ You definitely need validation
‣ And I’m not going to tell you how
Introduction to AtomPub Web Services • Ben Ramsey 46

47. That’s out of scope.

48. :-)

49. But I’ll show you the basics.

50. <?xml version="1.0" encoding="utf-8"?>
<service xmlns="http://www.w3.org/2007/app"
xmlns:atom="http://www.w3.org/2005/Atom"
xml:base="http://atom.example.org/">
<workspace>
<atom:title>Our Content Store</atom:title>
<collection href="user">
<atom:title>Users</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories href="cat/user"/>
</collection>
<collection href="content">
<atom:title>Content</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories href="cat/content"/>
</collection>
</workspace>
</service>

51. Get the Categories
Introduction to AtomPub Web Services • Ben Ramsey 51

52. GET /cat/content HTTP/1.1
Host: atom.example.org
HTTP/1.x 200 OK
Date: Mon, 22 Sep 2009 09:39:26 GMT
Content-Type: application/atomcat+xml

53. <?xml version="1.0"?>
<app:categories
xmlns:app="http://www.w3.org/2007/app"
xmlns:atom="http://www.w3.org/2005/Atom"
fixed="yes"
scheme="http://atom.example.com/cat/content">
<atom:category term="audio"/>
<atom:category term="video"/>
<atom:category term="game"/>
</app:categories>

54. Create the Entry Document Locally
Introduction to AtomPub Web Services • Ben Ramsey 54

55. <?xml version="1.0" encoding="utf-8"?>
<entry xmlns="http://www.w3.org/2005/Atom"
xml:base="http://atom.example.org/">
<title>Perfect</title>
<author>
<name>Mark Phelps</name>
</author>
<id>tag:example.org,2009:content/perfect</id>
<published>2009-09-22T20:12:08Z</published>
<category term="audio"
scheme="http://atom.example.com/cat/content"/>
<content type="application/mp4">
TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWF
IHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGl
...
</content>
</entry>

56. POST /content HTTP/1.1
Host: atom.example.org
Content-Type: application/atom+xml;type=entry
{body here}
HTTP/1.x 202 Accepted
Date: Mon, 22 Sep 2009 09:14:59 GMT
{body contains status indicator}

57. Authentication?
‣ Atom doesn’t specify a preference
‣ WSSE Username Token
‣ OAuth
‣ Basic authentication
‣ Digest authentication
‣ ???
Introduction to AtomPub Web Services • Ben Ramsey 57

58. Did I miss anything?

59. Oh, yeah.
Where’s the PHP code?

60. AtomPub in PHP
‣ DOM for reading/writing
‣ SimpleXML for reading
‣ XMLReader for reading
‣ XMLWriter for writing
‣ String concatenation for writing
‣ I recommend XMLReader/XMLWriter; they’re the fastest at parsing and
generating XML
Introduction to AtomPub Web Services • Ben Ramsey 60

61. Wrapping Up
‣ You can extend Atom with other XML vocabularies (Dublin Core, etc.)
‣ XML Digital Signature or XML Encryption may be used, or encrypt as a
bag of bits
‣ Use your preferred authentication method
‣ Use HTTP in a RESTful fashion
‣ Use DOM or XMLReader/XMLWriter to parse Atom documents
Introduction to AtomPub Web Services • Ben Ramsey 61

62. Questions?
‣ I blog at benramsey.com
‣ I tweet at @ramsey
‣ Please rate this presentation: http://joind.in/2185
‣ Read the Atom specifications:
RFC 4287
RFC 5023
‣ My company is Moontoast
Introduction to AtomPub Web Services • Ben Ramsey 62

63. Introduction to AtomPub Web Services
Copyright © Ben Ramsey. Some rights reserved.
This work is licensed under a Creative Commons
Attribution-Noncommercial-No Derivative Works 3.0
United States License.
For uses not covered under this license, please
contact the author.

64. Photo Credits
‣ Molecule display, by Christian Guthier
‣ Atom, by jayneandd
‣ Atomium - detail, by Constantin Barbu
‣ Simplicity, by Subterranean Tourist Board
‣ STEREO's Extreme UltraViolet Imager (EUVI), by NASA
‣ Quantum Universe, by Gaurav
‣ Fullerene Nanogears, by NASA
‣ Little Atom, by Marrio
‣ That Atom, by Albert O’Conner
‣ Bokeh Spiral, by Eric Wüstenhagen
‣ Chambered Nautilus Shell - detail, by Jitze Couperus
Introduction to AtomPub Web Services • Ben Ramsey 64