TREE Profile specification

1. Introduction

This specification introduces profiles for serializations such as [n-triples], [n-quads], [turtle] and [TRiG] to first contain a group for the hypermedia, and then contain groups for the members. The profile is optional to implement, yet comes with the benefit that it allows TREE clients to speed up extracting members and process them in a streaming fashion. The TREE profile does this by promising to a TREE client that the triples about the members are going to be bundled together.

2. Discovering the profile through the content-type header

There are two ways in which a client MAY discover the fact that the TREE profile has been used.

1. The server add ;profile="https://w3id.org/tree/profile" to the content-type headers on top of their [turtle], [n-quads], [turtle] or [TRiG] responses, such as Content-Type: text/turtle;profile="https://w3id.org/tree/profile.

2. The server uses for their node links a .tree prefix in the suffix of the file format. E.g., https://example.org/file.tree.nq.

3. An example

@prefix ex: <https://example.org/> .
@prefix tree: <https://w3id.org/tree/> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.

# The document starts with hypermedia controls
<> tree:relation [
    a tree:GreaterThanOrEqualToRelation ;
    tree:node <?greaterThanOrEqualTo=10>;
    tree:value 10;
    tree:remainingItems 10 ;
    tree:path ex:value
] .

ex:Collection1 a tree:Collection;
            tree:view <> ;
            rdfs:label "A Collection of 2 subjects"@en;
# `tree:member` indicates the hypermedia group is done, and the first member begins
            tree:member ex:Subject1 .

ex:Subject1 a ex:Subject ;
            rdfs:label "Subject 1" ;
            ex:value 2 ;
            ex:linkedTo [ a ex:Subject ] .

# Start of the second member
ex:Collection1 tree:member ex:Subject2 .
ex:Subject2 a ex:Subject ;
            rdfs:label "Subject 2" ;
            ex:value 9 ;
            ex:linkedTo ex:Subject1 .
# EOF flags the end of the second member

4. Implementing a TREE profile client

The client in this case MUST use a parser that retains triple order as in the original document.

When the profile is set (see profile), the client MAY implement the profile algorithm and not perform the steps indicated by the Member Extraction Algorithm. In this case, a client MUST assume the document starts with a hypermedia block. It then follows three simple rules:

1. From the moment the tree:member property is used, a new bundle of member quads will start.

2. From the moment the base IRI (<>) is used in the subject position, or when a tree:view property is used, a new block of hypermedia starts.

3. When end of file is encountered, the currently active block is closed.

Each member SHOULD be emitted from the moment it has been extracted. The client MUST wait for the end of the file before emitting the hypermedia.