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Link Relations: up/down vs parent/child vs ancestor/descendant etc.
I am busy designing a protocol for cloud computing and want clients to be able to discover children of a given resource in order to navigate a tree structure. I had been considering defining a new "collection" link relation but then found draft-divilly-atom-hierarchy
which defines a "down" relation.
My concern is that the terms "up" and "down" are ambiguous in this context and indeed we may end up defining [URI] relations for "up" and "down" as state changes for network resources. Furthermore there has been come commentary/confusion of late around the use of multiple attributes (e.g. "up up up") and now seems as good a time as ever to clarify given we have the link relation I-D and HTML 5 WD on the table at the IETF and W3C respectively.
I wonder whether it would be possible to instead use "parent" and "child" (for first generation relationships) or "ancestor" and "descendant" (for more generic n-generation relationships, where n is specified as an attribute like "level=2")? This is simple and self-describing and could resolve the issue once and for all. Alternatively the terms could be abbreviated to "asc" and "desc" respectively (as in "ascend" and "descend").
I also wonder whether "collection" isn't a bad idea anyway - consider a resource describing a bookshelf where the collection consists of books.