Tuesday, June 8, 2010

Please Accept: application/hal+xml

Here's an example of something I'm calling the 'Hypermedia Application Language' (hal):


Hal just defines a standard way to express hyperlinks in xml via a simple <link> element. The link element has the following attributes: @rel @href @name
  • Simple links can be written as solo/self-closing tags.
  • Links used to indicate embedded representations from other resources should be written with open and close tags, with the embedded representation contained within.
  • The root element must always be a link with an @rel of self and an appropriate @href value.
  • @name must be unique between all links in a document with the same @rel value, but is not unique within the entire document. i.e. a link element cannot be referred to by @name alone (thanks to Darrel for this)
  • @href value may contain a URI template
Some questions that have arisen for me:

What can/can't you do with this media type?

Did I just reinvent RDF/XML?

Is it enough to implement a system with this media type and to provide documentation to clients as "application specs" or "flow specs" describing the various ways link relations can be traversed to get stuff done?

As usual - all thoughts, comments, suggestions welcome! :)