RSS Versions and Modules
There are two main versions of the RSS format in use today; RSS
0.9x and RSS 1.0. Although the numbers might lead you to believe
that 1.0 replaces 0.9x, both are being actively used and developed.
Each version has its benefits and drawbacks; RSS 0.9x is known for
its simplicity, while RSS 1.0 is more extensible and fully
specified. Both formats are XML-based and have the same basic
structure.
People tend to get into heated discussions about the better
format. Ultimately, it's a choice you shouldn't worry too much over;
good RSS tools and aggregators will understand both formats. This
section presents a quick overview of each; for more information, see
their specifications and supporting materials.
RSS 0.9x (the 'x' is for the last digit; as of writing, RSS 0.94
is in development) was designed by Netscape Communications and
UserLand software, and is championed by
UserLand's Dave Winer. In
this version, RSS stands for "Really Simple Syndication," and
simplicity is its focus.
This branch of RSS is based on RSS 0.91, which was first
documented at Netscape and later
refined by
Userland.
Included in 0.92
- the latest stable version - are channel metadata like link,
title, description; image,
which allows you to specify a thumbnail image to display with the
feed); webMaster and managingEditor, to
identify who's responsible for the feed, and lastBuildDate,
which shows when the feed was last updated. Items have the standard
link, title and description
metadata, as well as other, more experimental
facilities like enclosure, which allows attachments to
be automatically downloaded (don't expect these features to be
supported by all aggregators, however).
RSS 0.9x takes a versioned approach to extensibility; new
features are added by declaring a new version of RSS in the 0.9
series. Winer controls the release of new versions, so if you have
suggestions about the future of RSS 0.9x, it's best to talk to him.
Here's an example of a minimal RSS 0.9x feed:
<?xml version="1.0"?>
<rss version="0.91">
<channel>
<title>Example Channel</title>
<link>http://example.com/</link>
<description>My example channel</description>
<item>
<title>News for September the Second</title>
<link>http://example.com/2002/09/01</link>
<description>other things happened today</description>
</item>
<item>
<title>News for September the First</title>
<link>http://example.com/2002/09/02</link>
</item>
</channel>
</rss>
RSS 1.0 stands for "RDF Site Summary." This flavor of RSS
incorporates RDF, a
Web standard for metadata. Because RSS 1.0 uses RDF, any RDF
processor can understand RSS without knowing anything about it in
particular.
RSS 1.0 also uses
XML Namespaces
to allow extensions - called RSS Modules - to be added
without worrying about conflicts. This is because RSS 1.0 doesn't
use a central person for extending the format; instead, namespaces
are used to describe a space for your own extensions. For example,
if you had an ISBN module to track books, it might look like this;
<item xmlns:book="http://namespace.example.com/book/1.0"
rdf:about="http://www.amazon.com/exec/obidos/tg/detail/-/0553575376">
<title>Excession</link>
<link>http://www.amazon.com/exec/obidos/tg/detail/-/0553575376</link>
<book:isbn>0553575376</book:isbn>
</item>
Generally, though, you should look for available RSS Modules,
rather than defining your own, unless you're sure that what you need
doesn't exist.
RSS 1.0 feeds look very similar to RSS 0.9x feeds, with a few key
differences;
- The entire feed is wrapped in
<rdf:RDF> ...
</rdf:RDF> elements (so that processors know that it's RDF)
- Each
<item> has an rdf:about
attribute that usually, but not always, matches the <link>;
this assigns an identifier to each item
- There's an
<items> element in the channel
metadata that contains a list of items in the channel, so that RDF
processors can keep track of the relationship between the items
- Some metadata uses the
rdf:resource attribute to
carry links, instead of putting it inside the element.
RSS 1.0 is developed and maintained by an ad hoc group of
interested people; see their Web site for
more information about RSS 1.0
and RSS Modules. See below for an example of an RSS 1.0 feed. |
