Blogs & feeds

Jim des RivieresOct. 16, 2008

• Grappling with question of how to present Jazz/OSLC data resources

• “Pure” data resources are presentation-free

• Okay for programmatic clients - robots

• But how do they get presented to humans???

• Blogs and Atom/RSS feeds– Has similar issues

• Ask: How do blogs and feeds work?

• Mine for ideas on how to solve for Jazz

• Blogs are hosted at web sites

• Native blog page is text/html• Page generated by blogging web site

• Page has blog entries embedded in it

• Browsers have hard-wired support for feeds (Atom and RSS)

• Each blog has an associated feed

• Browser discovers feed links from special <link> elements in HTML header

• Browser presents feeds using hard-wired feed view

• Feed is XML document - application/atom+xml• Generated by blogging web site

• Feed has blog entries embedded in it

• Browser recognizes feed by inspecting XML– Looks for <feed> as root document element– Looks for Atom XML namespace

• Browser ignores Content-Type response header– Works if document is text/plain

• Browsers feed view allows navigation to blog

• Browser discovers this from special <link> element in feed header

• Subscribe to feed pops up browser dialog to add to browser favorites

• Feed entries may contain other info that is not presented by browser feed view…– Comments on entries is not an Atom concept

• …but do show up in native blog view– Comments on entries is known to blog site

• Feed entries may also contain info that is presented by neither native blog page nor browser feed view

• Feed entries have their own URLs

• Feed entries have links back to native blog entry

• Feed document sometimes carry XML stylesheets– Used to make XML document directly renderable by browsers– Browser applies XML stylesheet (CSS, XSL) to XML document

• Ignored by hard-wired browser feed view

• XML feed rendered with XML stylesheet (simulated)

• Different XSL style sheet

• XML feed rendered with XML stylesheet (simulated)

Feed aggregation

• Aggregation sites collect entries from various feeds

• Presents entries through its own native view

• Links in aggregated blog entries refer to original blog entry

• Allowing navigation back to native blog page

• Aggregation site also publishes its own feed

• Which is viewable with browser feed view (like any other feed)

• Links in feed entries refer to original blog entry

• Allowing navigation back to native blog page

Recap – Story so far

• User does not choose presentation of blog entry

• Choice of presentation is determined by how user gets to blog entry

Feed readers

• Give users (as opposed to authors) a way to aggregate entries from diverse feeds

• Two main types– Web-based– Desktop tool

Web-based feed readers

• Nothing extra installed on client machine– Not even browser plug-in/add-in

• All preferences/state maintained on remote web server

• Web-based feed readers

• Allow you to…

• …to discover feeds

• …and to subscribe to them

• New entries are presented in web feed reader• Disappear from sight once read

• Some links in blog entries refer to original blog entry

• Allowing navigation back to native blog page

• Some links in blog entries are within the web feed reader

• Allowing in-place browsing of feeds that you’ve subscribed to

• Adding subscription from feed URL• Who reads feed document? Browser? Web feed reader

server?

• Browser talks to web feed reader server exclusively• Browser POSTs subscribe request to reader server API• Reader server retrieves and processes feed• Browser GETs list of unread items via reader server API

Desktop feed readers

• Desktop app installed on client machine

• Preferences/state maintained on client– Sometimes on remote server (optionally)

• Desktop feed readers

• Let you subscribe to feeds

• New entries are presented in feed reader

• Disappear from sight once read

• Some links in blog entries refer to original blog entry

• Allowing navigation back to native blog page• Opened in-place with browser widget

Feedburner

• Some blogs use feedburner

• Navigation from blog entry…

• …redirects to feed view on feedburner.com

• Lets you subscribe with popular web feed readers

• Hyperlinks go to web feed reader server– Pass feed URL as parameter

• Also lets you subscribe with popular desktop feed readers

• As well as navigate to feed document

• Hyperlink to feed XML

• For viewing in browser feed view

Recap

• Blogs and blog entries have URLs• Presentation level - HTML document• http://inside-swt.blogspot.com/• http://planet-oti.muellerware.org/

• Feeds and feed entries have URLs• Data level - XML document• http://inside-swt.blogspot.com/feeds/posts/default• http://planet-oti.muellerware.org/atom.xml

• Rich cross-linking– Within levels– Across levels

Recap

• Each feed/entry resource has a native web presentation

Recap

• Use special <atom:link> elements embedded in feed resource

• Uses special <html:link> elements embedded in HTML resource

• Does not use content negotiation– (except for a few anomalies with feedburner)

Recap

• Story relies in places on browser built-in feed view– Allows direct hyperlinking from presentation to

data level– Allows feed URL to be typed in to browser

Recap

• Many, many presentations for a blog entry– Native presentation at originating blog– Each browser feed view

• Slightly different for each browser

– Native presentation at each aggregation site– Web-based feed readers– Desktop feed readers

Recap

• User does not choose presentation of blog entry

• Choice of presentation is determined by how user gets to blog entry

• User is free to choose which feed reader to use– Optional

Thanks

• Fiddler Web Debugging Proxy– Free Microsoft tool for Windows– Lets you inspect HTTP traffic that IE sends– Approved for individual IBM-internal use– http://www.fiddler2.com/fiddler2/