Shelley Powers - What Are Syndication Feeds

What Are Syndication Feeds By Shelley Powers ............................................... Publisher: O'Reilly Pub Date: December 2005 Print ISBN-10: 0-596-52697-0 Print ISBN-13: 978-0-59-652697-9 Pages:

When you enter the world of syndicated content, you're oftenfaced with the question of what is the "proper" way to dosyndication. While syndication feeds have become a standardtool on the Web--you've seen their signposts: a littleorange button labeled XML in white letters, or maybe buttonsthat say Atom, RSS 2.0, RSS 1.0, or even Feed--it isimportant that your syndication feed be an extension of yoursite. It should reflect your interests, your concerns, andyour choices. This edoc will help you learn about thesepervasive little blobs of XML markup: their purpose, theelements that make up a feed, the different formats, and thetools for generating and consuming feeds. The tutorial starts with a succinct description of what afeed really is, then it covers: What Makes Up a Feed: A look at the commoncontainer and entry elements for a feed, and what theydo. Industry Support: An overview of the majorplayers and tools for syndicationfeeds. Discovering Feeds: How to make your siteeasy to subscribe to. Subscribing To and Reading Feeds: A look atvarious aggregators and how to usethem. Which Feeds Work Best for You: Should youuse RSS 1.0, RSS 2.0, or Atom? Or all of them? Here's how todecide. This tutorial will help you get your syndication feed up andrunning, so you can then forget about it and focus insteadon what's really important at your site: the content you areproviding to the world.

About the Author

Shelley Powers is an independent contractor who specializes in technology architecture and software development. She's authored several computer books, including Developing ASP Components, Unix Power Tools 3rd edition, Essential Blogging , and Practical RDF . In addition, Shelley has also written several articles related primarily to web technology, many for O'Reilly.

The feed "container" is information about the overall site that provides the feed, consisting of several fields that are listed once for the entire feed. Included within this container are the following fields that repeat across most syndication feeds:

link

This is the link for the site's URL, such as the weblog's URL.

title

This is the title for the site, such as the weblog's title.

description

This is a description of the weblog or site, and usually contains whatever subtitle is given for the site. In Atom, this is the subtitle field.

author

In Atom, author is a structure containing the author's name and email, or just the author's email. In RSS 2.0, this field is replaced by webMaster and managingEditor , which are email addresses. In RSS 1. x , this is replaced, usually, by dc:creator (which may be either a structure or a simple value).

date

In RSS 1. x , this field, usually dc:date , is the date the feed was updated. In Atom, this is the updated field; in RSS 2.0, this is the lastBuildDate .

generator

In RSS 2.0, this is the tool used to generate the syndication feed. The Atom feed also uses generator , while RSS 1. x uses generatorAgent .

copyright

Copyright information.

language

What language the text of the document is in.

id

This field is specific to Atom, and provides a unique identifier for the site.

image

An icon or image representing the feed or site for both RSS 1. x and RSS 2. x . In Atom, this would be icon , though logo can be used for a logo representation. In RSS 1.1 and RSS 2.0, image is a structure pointing to the image's URL, title, and link to site. In RSS 1. x , the image should be 88x31. In Atom, the icon "should have an aspect ratio of one (horizontal) to one (vertical), and should be suitable for presentation at a small size." In RSS 2.0, the image should have a maximum width of 144, and maximum height of 400; default is 88x31.

(Note that these aren't all the elements for each fieldjust those that are required and the most commonly occurring optional elements.)

Let's see some examples of feeds. The following is the head section of an Atom feed from O'Reilly's Radar weblog:

O'Reilly Radar 2005-10-13T17:13:35Z http://radar.oreilly.com/ tag:radar.oreilly.com,2005://24 Movable Type Copyright (c) 2005, O'Reilly Media, Inc....

In the example, notice the modified date, title , and copyright notice. Here the field link identifies the feed's relationship with the document.

A RSS 1.0 feed from the same site looks like:

O'Reilly Radar http://radar.oreilly.com/ http://radar.oreilly.com/ 2005-10-13T08:47:28-08:00 ...

Notice that the first XML element is the main rdf:RDF , required for all RDF/ XML documents. Other than that, it is very similar to the Atom feed, other than some name differences and changes in the namespaces (the acronym identifiers that are located at the beginning of the document and are used to point to the schema where the elements arise).

There is one major difference between RSS 1.0 and the other syndication feeds, and that is that all the items included in RSS 1.0 feeds are first listed in a container- like element, and are then defined in full in other parts of the document. This container looks as follows:

O'Reilly Radar doesn't have an RSS 2.0 feed (discussed later in this article), so I pulled a sample from the Scripting News weblog of Dave Winer. Dave is the creator of RSS 2.0, a sample of which follows:

Scripting News http://www.scripting.com/ It's even worse than it appears. en-us Copyright 1997-2005 Dave Winer Thu, 13 Oct 2005 04:00:00 GMT Thu, 13 Oct 2005 15:42:37 GMT http://blogs.law.harvard.edu/tech/rss UserLand Frontier v9.0.1 dwiner@cyber.law.harvard.edu dwiner@cyber.law.harvard.edu ...

The use of namespaces in RSS 2.0 is fairly rare, but has become more common as other companies such as Microsoft and Apple have added discussion , something else discussed later in the article.

These are examples of the feed's head section. What goes into the entry sections is discussed later, with examples for entries included.

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Note: Syndication feeds are created automatically using various tools, usually built into whatever tool you're using to create your website. These examples are provided purely for reference purposes, not as a guide in how to create a feed.

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Each individual entry at a site has its own entry within the feed, up to the number designated for each feed (this number does change, but usually ends up being between 5 and 15). In Atom, the entries are designated by entry elements, while in RSS 1. x and RSS 2.0, they're listed as item .

Examining the more comment elements within each entry:

title

The entry's title, if any.

link

The link or URL for the individual item.

guid

The unique identification of the item. In Atom, this is id .

description

In RSS 1.1 and RSS 2.0, the description is a text description or summary of the item. In Atom, the field for this value is summary .

content

The content is the encoded full content for the item, including any HTML or XHTML markup. The field could also be called content:encoded with RSS 1. x . If you specify both content and description , then the description (or summary ) should be an abbreviated copy of the text. If you specify just the summary or description , and don't want to provide full content, you should not include the content field.

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