e.g in-reply-to followed in reverse direction allows discovery of comments
Linked Data Fragments
Pieces of data and information on the Web can be connected to each other. This is because the Web is filled with hypermedia controls: most HTML pages contain several hyperlinks, some pages also contain forms with text fields and buttons. HTML is not the only format with hypermedia support; specific RDF vocabularies can be used to express hypermedia controls as well. Regardless of format, what all hypermedia controls on the Web have in common is that they somehow lead to an URL a client can visit. The following definition generalizes this notion.
A hypermedia control is a function that generates an IRI [RFC3987] based on zero or more arguments. In particular, a hyperlink is a zero-argument function (i.e., an IRI), and a hypermedia form is a multi-argument function.
Triple Pattern Fragments
This hypermedia control must be present because there purposely does not exist a fixed URL format that servers of Triple Pattern Fragments need to follow. This means that clients of Triple Pattern Fragments must not need prior knowledge of a server, i.e., they must not assume a certain URL pattern. Instead, clients must interpret the hypermedia control in each Triple Pattern Fragment in order to retrieve another fragment. Clients must not attempt to deconstruct the URL of a fragment, i.e., they must treat fragment URLs as opaque identifiers.