(2) Abstract

The feed formats RSS and Atom are read-only formats, and the Atom Publishing Protocol (AtomPub) builds on top of Atom and provides a protocol for submitting new items to feeds. AtomPub is a good example for a RESTful protocol that exposes all resources through URIs, allows to explore resources by following typed links, and allows interactions with resources based on the uniform interface defined by HTTP.

(3) Syndication Format Protocols

• LiveJournal (very simple text-based protocol)
  • not very good at handling structures (re-inventing for encoding structure)
• Blogger (now at Google [http://code.google.com/apis/blogger/overview.html] after Google bought Pyra [http://web.archive.org/web/20031008161432/http://weblog.siliconvalley.com/column/dangillmor/archives/000802.shtml])
  • no support for titles or any other sort of entry metadata
  • protocol from the early days of blogging before tagging became popular
• MetaWeblog [http://www.xmlrpc.com/metaWeblogApi] (an attempt to improve Blogger)
  • extends Blogger using a very bad design (RSS XML as XML-RPC structure encoded as XML)
• Atom Publishing Protocol (AtomPub) is an attempt to provide a clean alternative
  • use the same document structures for feeds and the protocol interacting with them
  • use a REST approach to provide a simple and Web-compatible protocol
  • add Service Documents [Service Documents (1)] and Category Documents [Category Documents (1)] for additional tasks

(4) RESTified Syndication

• Atom is a format for retrieving a set of entries as a feed document
  • feeds often are time-based and are refreshed periodically or whenever needed
  • feeds can use any other strategy for deciding what to publish
• Read-only access to feeds should be complemented by full access
  • full access needs the CUD out of the CRUD set of operations
  • many Web-centric technologies try to build on the Web's REST model of interaction
• AtomPub builds on Atom and adds a REST-based protocol on top of it
  • POST for creating new entries (sending the request to the collection)
  • PUT for updating existing entries (overwriting the existing entry)
  • DELETE for deleting entries from a collection

(5) Collections, Members, Entries, Media

• AtomPub's top-level concept is a collection
  • collections are used for managing and organizing members
  • Atom feed documents are the representation of collections
• Members of a collection can be entry and media resources
  • entry resources represent metadata and are represented as Atom entries
  • media resources can have any media type and are the data described by entries
  • a media link entry is an entry associated with a member

(6) Protocol Summary

(7) Service Documents

Service Documents represent server-defined groups of Collections, and are used to initialize the process of creating and editing resources.

• The real top-level construct of AtomPub is the workspace
  • collections on a server are organized into different workspaces
  • workspaces have no AtomPub semantics and no operations can be performed on them
• Service documents list constraints on the members of collections
  • accept specifies a comma-separated list of media ranges (with entry as special value)
  • categories defines the list of categories that can be applied to members (can be fixed)
  • AtomPub servers are likely to reject operations not satisfying these constraints

(8) Service Document Example

<service xmlns="http://purl.org/atom/app#" xmlns:atom="http://www.w3.org/2005/Atom">
 <workspace>
  <atom:title>Main Site</atom:title>
  <collection href="http://example.org/reilly/main">
   <atom:title>My Blog Entries</atom:title>
   <categories href="http://example.com/cats/forMain.cats"/>
  </collection>
  <collection href="http://example.org/reilly/pic">
   <atom:title>Pictures</atom:title>
   <accept>image/*</accept>
  </collection>
 </workspace>
 <workspace>
  <atom:title>Side Bar Blog</atom:title>
  <collection href="http://example.org/reilly/list">
   <atom:title>Remaindered Links</atom:title>
   <accept>entry</accept>
   <categories fixed="yes">
    <atom:category scheme="http://example.org/extra-cats/" term="joke"/>
    <atom:category scheme="http://example.org/extra-cats/" term="serious"/>
   </categories>
  </collection>
 </workspace>
</service>

(9) Category Documents

• Categories are important for creating and reading entries
  • they may contain metadata using any classification scheme
• Service Documents [Service Documents (1)] contain a list of allowed categories
• AtomPub defines a document format for standalone category documents
  • a useful interface between AtomPub systems and other systems using classification schemes

(10) Category Document Example

<app:categories xmlns:app="http://purl.org/atom/app#" xmlns="http://www.w3.org/2005/Atom" fixed="yes" scheme="http://example.com/cats/big3">
 <category term="animal"/>
 <category term="vegetable"/>
 <category term="mineral"/>
</app:categories>

(11) Semantic Web Light

• Syndication creates representations for universal concepts
• Atom adds some concepts to RSS's model
• Syndication revolves around the idea of interacting with items
• Atom-based interaction is one way of implementing REST
• For more semantics, Atom is only the foundation