Syndication: RSS, ATOM, APP, and All That

Elliotte Rusty Harold

elharo@metalab.unc.edu

http://www.cafeconleche.org/

• Cell Phones
• Pagers
• Alarm Watches
• etc.
• and set your notebook's volume to zero

• Who's using a Weblog client now?
• Anyone publishing their own blog?
• Demo Vienna
• This is not Usenet
• Is this the Web?
• It is HTTP; and it is XML

• Ongoing
• Daily Kos
• Mokka mit Schlag
• City Birder
• Scobleizer
• Re-imagineering

• At some point qualitative becomes quantitative
• Technically, blogging is no different than publishing a web page
• A phase shift?
• Comments?
• Openness wins. The fewer hoops one has to jump through the more successful something is.
• The web finally becomes as much fun as e-mail and Usenet
• Search and archiving take it to the next level.

• Issue trackers
• Newspapers
• Weather Info
• CVS Commits
• Stock Tickers
• TV Schedules
• Usenet
• Bird reports
• Sports Scores
• Package Tracking
• Coupons and sales
• Word a day
• Mailing lists
• What else?

• Duct tape
• Calculus
• Computers
• The Internet
• XML
• Atom

Suppose you think of your data as a list of, well, anything: stock prices or workflow steps or cake ingredients or sports statistics. Atom might be for you. Suppose the things in the list ought to have human-readable labels and have to carry a timestamp and might be re-aggregated into other lists. Atom is almost certainly what you need. And for a data format that didn’t exist a year ago, there’s a whole great big butt-load of software that understands it.

--Tim Bray,
Read the rest in Don’t Invent XML Languages

• Easy to cut apart and combine automatically
• Easy to sort
• Useful metadata
• Show headline feed on Cafe au Lait
• Consider the quote of the day

• The root channel has
  • title
  • link
  • description
  • language
  • image
• Plus items

• Each item has
  • title
  • link
  • description

• Length limits
• No embedded markup
• No namespace
• No DTD/schema
• IDs don't have to be unique

• 0.90: Designed by Netscape, based on RDF
• 0.91: no longer RDF compatible
• 0.92: removes length limits
• 0.93 abandoned
• 1.0: RDF based; Winer-less
• 2.0

• Removes length limits
• Makes language and children of item optional
• Adds source, enclosure, category, and cloud elements
• Explicitly allows escaped HTML in description element but doesn't identify it
• Spec

• From The Cafes

• From http://tbray.org/ongoing/ongoing.rss
• What's different?

• Adds guid element to uniquely identify items
• Adds ttl element to channel to indicate maximum number of minutes a channel can be cached without being reloaded
• Adds generator element to channel to indicate product that created the channel; e.g. WordPress
• Adds lastBuildDate element to channel to indicate when channel was last updated
• Allows elements from other namespaces
• Spec

• Resource Description Framework
• Based on Triples of form subject-predicate-object
• Subject has Property with Value
• Subjects, properties/predicates, and sometimes values are identified with URIs
• Allows for limited automated reasoning
• Tries to do to AI what the Web Did to Hypertext
• Underpinning of Semantic Web

• Metadata
• http://dublincore.org/documents/dces/
• Elements:
  • Title
  • Creator
  • Subject
  • Description
  • Publisher
  • Contributor
  • Date
  • Type
  • Format
  • Identifier
  • Source
  • Language
  • Relation
  • Coverage
  • Rights

• Put this in the head:

  <link rel="alternate" type="application/rss+xml" title="Cafe con Leche News" href="today.rss" />

• You can also use regular links
• Support varies from browser to browser

• Add an enclosure element to the RSS feed pointing to the MP3:

  ]]>

• There are also some optional iTunes extensions for Podcasts and Yahoo Media RSS extensions
• Example podcast RSS file

  
    
    Elliotte Rusty Harold
    http://www.elharo.com/podcasts/
    Java, XML, and Related Subjects
    Ranting and Raving
    Conference sessions and University classes on the subject of Java and XML
    en
    Elliotte Rusty Harold
    
      Elliotte Rusty Harold
      elharo@metalab.unc.edu
    
    
    
      http://www.elharo.com/images/headshot.jpg
      
      http://www.elharo.com/podcasts/
    
    Computers
    
    Java, XML, Birds
    no
    
      
      Elliotte Rusty Harold
      Which way leads out of the forest of Liars & Truth-tellers
      Which way leads out of the forest of Liars & Truth-tellers
      XML based syndication is moving from its foundations in weblogs to unexpected arenas: source code control systems, audio narrowcasts, e-mail, bug tracking, stock tickers, and more. News readers like Vienna, NetNewsWire, RSSOwl, and Newsgator are replacing classic web browsers for many uses. This session explores the fundamental technologies underlying this explosion of content: the various versions of RSS, OPML, Atom, and the Atom Publishing Protocol. Learn the tricks and techniques for integrating these XML applications into your products as both clients and serve
      
      http://www.nyphp.org/podcasts/RSS%20Atom%20APP%20and%20all%20that.mp3
      Tue, 28 Feb 2006 18:30:40 -0500
      Information Technology
      no
      01:34:32
      RSS, Atom, APP, OPML, XML
    

  
]]>

• RSS was hacked together in the early days of XML by novices
• Limited experience with how or where it would be used; some obvious needs and use cases were missed
• Atom is a second generation spec designed to do things properly
• Atom is replacing RSS fairly rapidly
• RSS is a frozen spec

• Categorized content
• Less flat, more nested
• Uses namespaces
• Well-formedness required
• Titles are required for entries
• mode attribute specifies whether payload of a text construct is escaped HTML, plain text, or real well-formed HTML, URL to content, some other XML format, or Base-64 encoded binary data
• Supports XML Encryption and XML Digital Signature on individual entries
• Item-level authors instead of one-per-feed
• RELAX NG schema
• xml:lang and xml:base

• First broadly adopted version of Atom
• Atom 0.3 Example: http://citybirder.blogspot.com/atom.xml
• You may have to consume this, but don't produce it.

• Namespace changes from http://purl.org/atom/ns# to http://www.w3.org/2005/Atom
• version attribute dropped
• id required on feed and entry
• Multiple author elements allowed
• copyright has become rights and is allowed on individual entry elements
• No info or created elements
• category element can replace Dublin Core
• url has changed to uri

• text/xml vs. application/xml
• application/rss+xml
• application/atom+xml
• .htaccess

  AddType application/rss+xml rss
  AddType application/atom+xml .atom
  AddDefaultCharset utf-8

• Anyone who can’t make a syndication feed that’s well-formed XML is an incompetent fool. - Tim Bray
• Check feeds for spec compliance
• http://feedvalidator.org/check?url=http://www.mozillazine.org/atom.xml

• Put this in the head:

  <link rel="alternate" type="application/atom+xml" title="Cafe con Leche News" href="fulltext.atom" />

• You can also use regular links
• Support varies from browser to browser

• Outline Processor Markup Language
• Used to export/import Weblog feeds
• Example
• No good spec and that's a problem

• Based on REST
• Pure GET
• What about writing?

• Blogger
• Metaweblog
• Movable Type
• WordPress
• APP

• Insecure
• Weak; no nested markup
• Underspecified
• Remember CORBA? RPC? IIOP?
• The Eight Fallacies of Distributed Computing by Peter Deutsch

The Atom Publishing Protocol is an application-level protocol for publishing and editing Web resources using HTTP [RFC2616] and XML 1.0 [W3C.REC-xml-20040204]. The protocol supports the creation of arbitrary web resources and provides facilities for:

• Collections: Sets of resources, which may be retrieved in whole or in part.
• Introspection: Discovering and describing collections.
• Editing: Creating, updating and deleting resources.

• Read the entries that exist
• Create new entries
• Update entries
• Comment on entries
• Delete entries

• It is a protocol. It is decoupled from implementation details.
• Used remotely by many different clients and types of clients:
  • Custom GUI programs
  • Web-based applications:
    • HTML forms
    • XForms
    • AJAX
  • Programs without human authors: stock tickers, weather info, lab monitors, etc.
  • Existing applications like OpenOffice
• On many different platforms:
  • Mac
  • Windows
  • Linux
  • Palm Pilot
  • Cell Phones
  • Cash Registers
• With authentication

• XML Documents
• Over HTTP
• Using the REST architectural style

• All resources are identified by an IRI
• GET retrieves a representation of a resource (side effect free)
• POST creates a new resource for which the server returns a URI
• PUT creates/replaces resource at a specified URI (idempotent)
• DELETE removes a resource
• Authentication may be required for any or all of these operations

• GET this from a known URL to enumerate the workspace on a server
• A workspace is a server-defined group of collections
• Example from the spec:

  This Introspection Document describes two workspaces. The first, called 'Main Site', has two collections called 'My Blog Entries' and 'Pictures' whose IRIs are 'http://example.org/reilly/main' and 'http://example.org/reilly/pic' respectively. 'My Blog Entries' is an Entry collection and 'Pictures' is a Media collection....

  The second workspace is called 'Side Bar Blog' and has a single collection called 'Remaindered Links' whose collection IRI is 'http://example.org/reilly/list'. 'Remaindered Links' is an Entry collection.

• application/atomserv+xml media type

• Thomas Boyer and Tim Bray for looking over and gently correcting these notes

• This presentation: http://www.cafeconleche.org/slides/albany/syndication/
• The myth of RSS compatibility: http://diveintomark.org/archives/2004/02/04/incompatible-rss
• RSS 2.0 and Atom 1.0, Compared (www.tbray.org)
• Atom Enabled: http://www.atomenabled.org/
• Atom Wiki
• The Atom specification: RFC 4287
• Atom Publishing Protocol: http://ietfreport.isoc.org/idref/draft-ietf-atompub-protocol/
• Wikipedia: http://en.wikipedia.org/wiki/Atom_(standard)