It seems there's been some recent hubbub in the world of podcasting about how to attach multiple binary files to a single post in an RSS feed In a post entitled Multiple-enclosures on RSS items? Dave Winer weighs in on the issue. He writes
This question comes up from time to time, and I've resisted answering it directly, thinking that anyone who really read the spec would come to the conclusion that RSS allows zero or one enclosures per item, and no more. The same is true for all other sub-elements of item, except category, where multiple elements are explicitly allowed. The spec refers to "the enclosure" in the singular. Regardless, some people persist in thinking that you may have more than one enclosure per item.
Okay, let's play it out. So if I have more than one enclosure per item, how do I specify the publication date for each enclosure? How do I specify the title, author, a link to comments, a description perhaps, or a guid? The people who want multiple enclosures suggest schemes that are so complicated that they're reduced to hand-waving before they get to the spec, which I would love to read, if it could be written. Some times some things are just too hard to do. This is one of them.
And there's a reason why it's too hard. Because you're throwing out the value of RSS and then trying to figure out how to bring it back. There's no need for items any more, so you might as well get rid of them. At the top level of channel would be a series of enclosures, and then underneath each enclosure, all the meta-data. Voila, problem solved. Only what have you actually solved? You've just re-created RSS, but instead of calling the main elements "item" we now call them "enclosure".
The value of RSS is fairly self evident to me but it seems that given the amount of people who keep wanting to reinvent the wheel it may not be as clear to others. As someone who used to work on core XML technologies at Microsoft, the value of XML was obvious to me. It allowed developers to agree to use the same data format for information interchange which led to a proliferation of a wide and uniform set of tools for working with data formats. XML is not an optimal format for most of the tasks it is used for but it more than makes up for this with the plethora of tools and technologies that exist for processing XML.
My expectation about XML was always that the software industry would move on to agreeing on other higher level protocols built on XML for application information interchange. So I've always been frustrated to see many attempts by various parties, including the W3C with efforts such as XML 1.1 and binary XML, take us steps back by wanting to fragment the interoperability promise of XML.
RSS is a wonderful example of the higher level of interoperability that can be built upon XML formats. Instead of information sources using various incompatible mechanisms for providing information to end users such as NOAA's SOAP web service and the Microsoft.com web services which each require a separate custom application to consume them, sites can all standardize on RSS. This standardization creates an ecosystem of applications that produce and consume RSS feeds which is a lot larger than what would exist for each site specific web services or market specific XML syndication formats. Specifically, it allows for the evolution of the digital information hub where users can view data from the various information sources they care about (blogs, news, weather reports, etc) in their choice of applications.
Additionally, RSS is extensible. This means that even if the core elements and attributes do not satisfy all the requirements of a particular problem domain, then domain-specific information can be added to the feed. This allows for regular consumers of RSS to still be able to consume the content while domain specific applications can give users a richer experience. This is a much better solution for both content producers and consumers than coming up with domain specific applications.
As a user I want less formats not more. I want my email to come in my RSS aggregator, I want my favorite newsgroups to show up in my RSS aggregator, I'm tired of having a separate application for what is essentially the same kind of data. In fact, it seems Google agrees with me as evidenced by them exposing XML feeds for your GMail inbox and for USENET newsgroups via Google Groups. Unfortunately, if you have a plain old RSS reader, you can't view these feeds and instead have to find an aggregator that supports Atom 0.3. Two steps forward, one step back.
We need less data interchange formats not more. It is better for content producers, better for end users and better for developers of applications that use these formats. Existing problems in syndication should focus on how to make the existing formats work for us instead of inventing new formats.
Vive la RSS.