XHTML2 defines a number of list constructs :

• dl - Definitions Lists: lists of terms with definitions.
• ul - Unordered Lists: lists with unordered items.
• ol - Ordered Lists: lists with ordered items.
• nl - Navigation Lists: lists with navigation items.

These elements clearly have semantic value regarding the information they contain.

RDF defines the type rdf:Container. A container is a single RDF node, linked to any number of other RDF nodes using the rdf:_1, rdf:_2, rdf:_3 ... properties. rdf:Container has 3 subtypes:

• rdf:Bag: the members of this container are unordered
• rdf:Seq: the members of this container are ordered
• rdf:Alt: the members of this container are options out of a set of alternatives

RDF also defines Collections, which provide null-terminated linked-lists of elements.

It does not appear that RDF Collections — null-terminated linked-lists — are the right semantic construct for XHTML. Thus, we make no attempt to provide syntactic sugar for RDF Collections. Instead, we focus on the RDF Containers: rdf:Bag and friends.

It is fairly clear that there is a semantic "match made in heaven" between the following:

• rdf:Bag corresponds to ul
• rdf:Seq corresponds to ol
• rdf:Alt corresponds to nl

dl is less clear, though it also appears to be an unordered set of elements.

IMPORTANT: for now, we do not address dl, as the semantics are more complicated and we want to get ul,ol, and nl right first.

Thus, we want the following XHTML2 syntax:

to result, via RDF/A, in the following triples:

Similarly, the use of ol would have generated the same RDF triples, with the exception of the rdf:type property set to rdf:Seq. The use of nl would have generated an rdf:type of rdf:Alt.

If the list element in XHTML is not given an id, then it is, of course, a bnode. The following XHTML:

results in:

An XHTML2 element that defines a list, ul, ol, or nl, automatically generates an RDF triple that defines the type of that node. The normal RDF/A rules of naming/bnode apply: if the element has id, then the rdf:type property is applied to the node identified as such. Otherwise, a bnode is generated to correspond to that XHTML element, and the rdf:type property is applied to this bnode. Note that the absence or presence of an about attribute on this list element does not affect this automatically generated triple: the subject of this automatic triple is still the list element.

An XHTML2 element that defines a list item, li, automatically indicates an implied RDF property. The processing rules are as follows, in the explicit order given:

1. The subject of this automatic assertion triggered by the li is the element's corresponding list node. Note that this is the case even if the list element has an about attribute.
2. If li has an href attribute, then a triple is generated with the corresponding list node as subject, the appropriate membership property (see below), and the href value as object. This may be in addition to another triple generated by an explicit rel attribute (which may resolve to a different subject).
3. If li has no href attribute, then a triple is generated with the corresponding list node as subject, the appropriate membership property (see below), and the li element content as a literal object. This may be in addition to the triple generated by an explicit property attribute (which may resolve to a different subject).

The appropriate membership property — rdf:_1, rdf:_2, ... — are exactly those for resolving rdf:li in RDF/XML: find the previous member in the collection as defined by the XML DOM, determine its membership property, and use the next one for the current li. If there is no previous member, use rdf:_1.

Beyond the above simple examples, the following examples show how to resolve more confusing setups.