for Content Publishers and Webmasters
Think about all of the information that you access on the Web on a
day-to-day basis; news headlines, search results, “What’s New”, job
vacancies, and so forth. A large amount of this content can be thought of as
a list; although it probably isn’t in HTML <li> elements,
the information is list-oriented.
Most people need to track a number of these lists, but it becomes difficult once there are more than a handful of sources. This is because they have to go to each page, load it, remember how it’s formatted, and find where they last left off in the list.
RSS is an XML-based format that allows the syndication of lists of hyperlinks, along with other information, or metadata, that helps viewers decide whether they want to follow the link.
This allows peoples’ computers to fetch and understand the information, so that all of the lists they’re interested in can be tracked and personalized for them. It is a format that’s intended for use by computers on behalf of people, rather than being directly presented to them (like HTML).
To enable this, a Web site will make a feed, or channel, available, just like any other file or resource on the server. Once a feed is available, computers can regularly fetch the file to get the most recent items on the list. Most often, people will do this with an aggregator, a program that manages a number of lists and presents them in a single interface.
Feeds can also be used for other kinds of list-oriented information, such as syndicating the content itself (often weblogs) along with the links. However, this tutorial focuses on the use of RSS for syndication of links.
A feed contains a list of items or entries, each of which is identified by a link. Each item can have any amount of other metadata associated with it as well.
The most basic metadata for an entry includes a title for the link and a description of it; when syndicating news headlines, these fields might be used for the story title and the first paragraph or a summary, for example. For example, a simple entry might look like;
<item> <title>Earth Invaded</title> <link>http://news.example.com/2004/12/17/invasion</link> <description>The earth was attacked by an invasion fleet from halfway across the galaxy; luckily, a fatal miscalculation of scale resulted in the entire armada being eaten by a small dog.</description> </item>
Additionally, the feed itself can have metadata associated with it, so that it can be given a title (e.g., “Bob’s news headlines”), description, and other fields like publisher and copyright terms.
For an idea of what full feeds look like, see ‘RSS Versions and Modules’.
Aggregators are the most common use of feeds, and there are several types. Web aggregators (sometimes called portals) make this view available in a Web page; my Yahoo is a well-known example of this. Aggregators have also been integrated into e-mail clients, users’ desktops, or standalone, dedicated software.
Aggregators can offer a variety of special features, including combining several related feeds into a single view, hiding entries that the viewer has already seen, and categorizing feeds and entries.
Other uses of feeds include site tracking by search engines and other software; because the feed is machine-readable, the search software doesn’t have to figure out which parts of the site are important and which parts are just the navigation and presentation. You may also choose to allow people to republish your feeds on their Web sites, giving them the ability to represent your content as they require.
Your viewers will thank you, and there will be more of them, because it allows them to see your site without going out of their way to visit.
While this seems bad at first glance, it actually improves your site’s visibility; by making it easier for your users to keep up with your site — allowing them to see it the way they want to — it’s more likely that they’ll know when something that interests them is available on your site.
For example, imagine that your company announces a new product or feature every month or two. Without a feed, your viewers have to remember to come to your site and see if they find anything new — if they have time. If you provide a feed for them, they can point their aggregator or other software at it, and it will give them a link and a description of developments at your site almost as soon as they happen.
News is similar; because there are so many sources of news on the Web, most of your viewers won’t come to your site every day. By providing a feed, you are in front of them constantly, improving the chances that they’ll click through to an article that catches their eye.
No! You still retain copyright on your content (if you wish to).
You also control what information is syndicated in the feed, whether it’s a full article or just a teaser. Your content can still be protected by your current access control mechanisms; only the links and metadata are distributed. You can also protect the RSS feed itself with SSL encryption and HTTP username/password authentication too, if you’d like.
In many ways, syndication is similar to the subscription newsletters that many sites offer to keep viewers up-to-date. The big difference is that they don’t have to supply an e-mail address, lowering the barrier of privacy concerns, while still giving you a direct channel to your viewers. Also, they get to see the content in the manner that’s most convenient to them, which means that you get more eyes looking at your content.
Any list-oriented information on your site that your viewers might be interested in tracking or reusing is a good candidate for a feed. This can encompass news headlines and press releases, job listings, conference calendars and rankings (like ‘top 10’ lists).
For example;
While it’s a good start to have a “master feed” for your site that lists recent news and events, don’t stop there. Generally, each area of your site that features a changing list of information should have a corresponding feed; this allows viewers to precisely target their interests.
For example, if your news site has pages for World news, national news, local news, business, sports, etc., there should be a feed for each of these sections.
If your site offers a personalized view of data (e.g., people can choose categories of information that will show up on their home page), offer this as a feed, so that the viewers’ Web pages match the content of their feeds.
A great example of this is the variety of feeds that Netflix provides; not only can you keep track of new releases, but also personalised reccommendations and even a listing of the movies in your queue.
Another good example is Apple’s iTunes Music Store RSS feed generator; you can customize it based on your preferences, and the views it allows match those provided in the Music Store itself.
Finally, remember that feeds are just as — if not more — useful on an Intranet as they are on the Internet. Syndication can be a powerful tool for sharing and integrating information inside a company.
There are a number of ways to generate a feed from your content. First of all, explore your content management system - it might already have an option to generate an RSS feed.
If that option isn’t available, you have a number of choices;
For more information about all of these options, see “Feed Tools” and “More Information”.
An important step after publishing a feed is letting your viewers know that it exists; there are a lot of feeds available on the Web now, but it’s hard to find them, making it difficult for viewers to utilize them.
Pages that have an associated RSS feed should clearly indicate this to viewers by using a link containing like ‘RSS feed’. For example,
<a type="application/rss+xml" href="feed.rss">RSS feed for this page</a>
where ‘feed.rss’ is the URL for the feed. the ‘type’ attribute tells browsers that this is a link to an RSS feed in a way that they understand.
Additionally, some programs look for a link in the <head> section of your HTML. To support this, include a <link> tag;
<head> <title>My Page</title> <link rel="alternate" type="application/rss+xml" href="feed.rss" title="RSS feed for My Page"> </head>
These links should be placed on the Web page that is most similar to the feed content; this enables people to find them as they browse.
Note that Atom feeds should use application/atom+xml rather than
application/rss+xml in both styles of use.
Finally, there are a number of guides and registries for RSS feeds that people can search and browse through, much like the Yahoo directory for Web sites; it’s a good idea to register your feed; see More Information.
There are a number of different versions of the RSS format in use today, but the main choices are RSS 1.0 and RSS 2.0. Each version has its benefits and drawbacks; RSS 2.0 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.
There’s one more choice; Atom is an effort in the IETF (an Internet standards body) to come up with a well-documented, standard syndication format. Although it has a different name, it has the same basic functions as RSS, and many people use the term “RSS” to refer to RSS or Atom syndication.
This section presents a quick overview of each; for more information, see their specifications and supporting materials.
RSS 2.0 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 2.0.1 - the
latest stable version of this branch — 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). Finally, items can have
a guid element that identifies the item uniquely; this allows some
advanced functionality in some aggregators.
Here’s an example of a minimal RSS 2.0 feed:
<?xml version="1.0"?>
<rss version="2.0">
<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>
In the RSS 2.0 roadmap, Winer states that this branch is, for all practical purposes, frozen, except for clarifications to the specification.
However, exensions to the format are allowed in separate modules, using XML Namespaces to avoid conflicts in their names. 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 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. This allows syndicated feeds to easily become part of the Semantic Web.
RSS 1.0 also uses XML Namespaces to allow extensions, in a manner similar to RSS 2.0.
RSS 1.0 feeds look very similar to RSS 2.0 feeds, with a few key differences;
<rdf:RDF> …
</rdf:RDF> elements (so that processors know that it’s
RDF)<item> has an rdf:about attribute
that usually, but not always, matches the <link>; this
assigns an identifier to each item<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 itemsrdf: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.
The most well-known example of an RSS 1.0 Module is the Dublin Core Module. The Dublin Core is a set of metadata developed by librarians and information scientists that standardizes a set of common metadata that is useful for describing documents, among other things. The Dublin Core Module uses these metadata to attach information to both feeds (in the channel metadata) and to individual items.
This module includes useful elements like dc:date, for
associating dates with items, dc:subject, which can be useful
for categorizing items or feeds, and dc:rights, for dictating
the intellectual property rights associated with an item or a feed.
Here’s an example of a minimal RSS 1.0 feed that uses the Dublin Core Module:
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns="http://purl.org/rss/1.0/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
>
<channel rdf:about="http://example.com/news.rss">
<title>Example Channel</title>
<link>http://example.com/</link>
<description>My example channel</description>
<items>
<rdf:Seq>
<rdf:li resource="http://example.com/2002/09/01/"/>
<rdf:li resource="http://example.com/2002/09/02/"/>
</rdf:Seq>
</items>
</channel>
<item rdf:about="http://example.com/2002/09/01/">
<title>News for September the First</title>
<link>http://example.com/2002/09/01/</link>
<description>other things happened today</description>
<dc:date>2002-09-01</dc:date>
</item>
<item rdf:about="http://example.com/2002/09/02/">
<title>News for September the Second</title>
<link>http://example.com/2002/09/02/</link>
<dc:date>2002-09-02</dc:date>
</item>
</rdf:RDF>
As you can see, RSS 1.0 is a bit more verbose than 2.0, mostly because it needs to be compatible with other versions of RSS while containing the markup that RDF processors need.
Both RSS 1.0 and 2.0 are informal specifications; that is, they aren’t published by a well-known standards body or industry consortium, but instead by a small group of people.
Some people are concerned by this, because such specifications can be changed at the whim of the people who control it. Standards bodies bring stability, by limiting change and having well-established procedures for introducing it. To introduce such stability to syndication, a group of people established an IETF Working Group to standardise a format called Atom.
Atom is functionally similar to both branches of RSS, and is also an XML-based format.
For example;
<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title>Example Feed</title>
<link href="http://example.org/"/>
<updated>2003-12-13T18:30:02Z</updated>
<author>
<name>John Doe</name>
</author>
<id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
<entry>
<title>Atom-Powered Robots Run Amok</title>
<link href="http://example.org/2003/12/13/atom03"/>
<id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
<updated>2003-12-13T18:30:02Z</updated>
<summary>Some text.</summary>
</entry>
</feed>
As you can see, Atom has a feed element that contains both the feed-level
metadata as well as the entrys (analogous to RSS’ items),
and entry can contain similar metadata, such as title,
link, id (instead of RSS 1.0’s rdf:about or RSS 2.0’s
guid), and a short textual summary (instead of RSS’
description).
Generally, Atom isn’t as widely supported as RSS 1.0 or 2.0 right now, because it’s relatively new. However, it should catch up quickly, because of the broad base of vendors supporting the standardisation effort.
One of the most confusing and unfortunate problems in syndication is the large number of formats in use. In addition to those listed above, there are many other formats (e.g., RSS 0.9, 0.91, 0.92) that are commonly encountered on the Web.
For better or worse, the decision isn’t as critical as you might think. Most aggregators and other software use syndication libraries which abstract out the particular format that a feed is in, so that they can consume any popular syndication feed.
As a result, which format to choose is a matter of personal taste. RSS 1.0 is very extensible, and useful if you want to integrate it into Semantic Web systems. RSS 2.0 is very simple and easy to author by hand. Atom is now an IETF Standard, bringing stability and a natural community to support its use.
RSS and Atom are easy to work with, but like any new format, you may encounter some problems in using them. This section attempts to address the most common issues that arise when generating a feed.
rdf:about (RSS 1.0),
guid (RSS 2.0) and id (Atom). This will save a lot of
headaches down the road.<title>, people may not know what the link is about.
By the same token, if you shove an entire article into
<description>, it’ll crowd people’s view of the feed,
and they’re less likely to stay interested in what you have to say.
Generally, you want to put enough into the feed to help someone decide
whether they should follow the link.<a href="...">,
<b> or <p>) in your RSS feed;
because you don’t know how it will be presented, doing so can prevent
your feed from being displayed correctly. If you need to include a a tag
in the text of the feed (e.g., the title of an entry is “Ode to
<title>”), make sure you escape ampersands and angle brackets (so
that it would be “Ode to <title>”). © and other common entities
available. You can define them in the XML, or alternatively just use an
character encoding that makes what you need available.<description> to dictate copyright
terms. Use the appropriate element or module.301 Moved Permanently) or is no longer available (410
Gone or 404 Not Found).This is an incomplete list of tools for creating feeds and checking them to make sure that you’ve done so correctly. Note that there are many more libraries that help parsing feeds; these haven’t been included here because this tutorial focuses on the Webmaster, not consumers of feeds.
This document is Copyright © 2002-2005 Mark Nottingham <[email protected]>. This work is licensed under a Creative Commons License.
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Although the author believes the contents to be accurate at the time of publication, no liability is assumed for them, their application or any consequences thereof. If any misrepresentations, errors or other need for clarification is found, please contact the author.
The latest revision of this document can always be obtained from http://www.mnot.net/rss/tutorial/
Translations are available in: Brazilian Portuguese.
Version 0.91 — September 7, 2005