Atom Compared to RSS 2.0

The main motivation for the development of Atom was dissatisfaction with RSS. Among other things, there are multiple incompatible and widely adopted versions of RSS. The intention was to ease the difficulty of developing applications with web syndication feeds.

A brief description of the ways Atom 1.0 seeks to differentiate itself from RSS 2.0 follows:

• RSS 2.0 may contain either plain text or escaped HTML as a payload, with no way to indicate which of the two is provided. Atom in contrast uses an explicitly labeled (i.e. typed) "entry" (payload) container. It allows for a wider variety of payload types including plain text, escaped HTML, XHTML, XML, Base64-encoded binary, and references to external content such as documents, video and audio streams, and so forth.

• RSS 2.0 has a "description" element which can contain either a full entry or just a description. Atom has separate “summary” and “content” elements. Atom thus allows the inclusion of non-textual content that can be described by the summary.

• Atom is defined within an XML namespace whereas RSS 2.0 is not.

• Atom specifies use of the XML's built-in xml:base for relative URIs. RSS 2.0 does not have a means of differentiating between relative and non-relative URIs.

• Atom uses XML's built-in xml:lang attribute as opposed to RSS 2.0's use of its own "language" element.

• In Atom, it is mandatory that each entry have a globally unique ID, which is important for reliable updating of entries.

• Atom 1.0 allows standalone Atom Entry documents whereas with RSS 2.0 only full feed documents are supported.

• Atom specifies that dates be in the format described in RFC 3339 (which is a subset of ISO 8601). The date format in RSS 2.0 was underspecified and has led to many different formats being used.

• Atom 1.0 has IANA-registered MIME-type. RSS 2.0 feeds are often sent as application/rss+xml, although it is not a registered MIME-type.

• Atom 1.0 includes an XML schema. RSS 2.0 does not.

• Atom is an open and evolvable standard developed through the IETF standardization process. RSS 2.0 is not standardized by any standards body. Furthermore according to its copyright it may not be modified.

• Atom 1.0 elements can be used as extensions to other XML vocabularies, including RSS 2.0 as illustrated in a weblog post by Tim Bray entitled "Atomic RSS".

• Atom 1.0 describes how feeds and entries may be digitally signed using the XML Digital Signature specification such that entries can be copied across multiple Feed Documents without breaking the signature.

• Despite the emergence of Atom as an IETF Proposed Standard and the decision by major companies such as Google to embrace Atom, use of the older and more widely known RSS 1.0 and RSS 2.0 formats has continued.

• RSS 2.0 support for enclosures led directly to the development of podcasting. While many podcasting applications, such as iTunes, support the use of Atom 1.0, RSS 2.0 remains the preferred format.

• Many sites choose to publish their feeds in only a single format. For example CNN, the New York Times, and the BBC offer their web feeds only in RSS 2.0 format.

• News articles about web syndication feeds have increasingly used the term "RSS" to refer generically to any of the several variants of the RSS format such as RSS 2.0 and RSS 1.0 as well as the Atom format. (For example, "Fine-Tuning Your Filter for Online Information" (NYT) and "There's a Popular New Code for Deals: RSS" (NYT January 29, 2006))

• Each of the various web syndication feed formats has attracted large groups of supporters who remain satisfied by the specification and capabilities of their respective formats.

• Atom supports multiple link elements per entry, a feature which can be used to specify enclosures of different types. This eliminates the need for separate feeds for podcasts that provide multiple file formats.