Hierarchical URIs

How should URIs be assigned to a group of resources that form a natural hierarchy?

Context

It is often the case that a collection of resources may form a natural hierarchy. E.g. the chapters within a book, or the departments within an organization. Reflecting this strict hierarchy within the URI structure makes those URIs more hackable allowing users/developers to "navigate" up the hierarchy by pruning the URI.

Solution

Where a natural hierarchy exists between a set of resources use Patterned URIs that conform to the following pattern:

:collection/:item/:sub-collection/:item

E.g. in a system which is publishing data about individual books and their chapters, we might use the following identifier for chapter 1 of a specific book:

/books/12345/chapters/1

The /chapters URI will naturally reflect to the collection of all chapters within a specific book. The /books URI maps to the collection of all books within a system, etc.

Example(s)

The discogs dataset in dataincubator uses hierarchical uris of the form:

http://discogs.dataincubator.org/release/22530/track/1-01

Discussion

This technique is best suited to scenarios where the items in the sub-collections (chapters) are always associated with a single parent item. Other relationships might exist, e.g. the chapter may be included in another but the chapter is always associated with at least one book: they do not exist in isolation. In circumstances where this doesn't hold true, then it is best to just use simple Patterned URIs.

The same applies to circumstances where the hierarchy may change over time.

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