HAL is a hypertext format for m2m interaction. It provides the following hypermedia factors:
- Embedded Links (LE)
- Out-bound navigational links (LO)
- Templated Queries (LT)
- Link relations(CL)
HAL specifies two elements:
- link
- resource
Both elements share the following attributes:
- @rel
- @href
- @name
The link and resource elements differ in the following ways:
Link elements..
- The link element is intended for representing out-bound links and should be written with solo/self-closing tags.
- @href value of a link element may contain a URI template to express a templated query link.
Resource elements..
- The resource element is intended for representing the embedded state of other resources and should be written with open and close tags, with the embedded representation contained within.
- The root element must always be a resource with an @rel of self and an appropriate @href value.
Other rules:
- @name must be unique between all HAL elements (link + resource) with the same @rel value in a document, but should not be considered unique within the entire document. This means a link element cannot be referred to by @name alone (thanks to Darrel for this)
- The subject of an @rel is always directed at the closest parent resource element.
e.g. A link that appears within an embedded resource relates to the embedded resource, and not the root resource.
Here is an example:
And here's how that might look in json:
