Ordering In Action
This final example will both illustrate a second use of ldp:DirectContainers as well as detail the PCDM recommendation for how to handle ordering of resources.
The addtional predicates/relationships that will be used in this example are:
- ore:proxyIn
- ore:proxyFor
- iana:first
- iana:next
- iana:prev
- iana:last
...all of which are further described in the Portland Common Data Model.
As in the book example, begin with creating an ldp:DirectContainer, "orderProxies/", as a child of the book, "raven/", resource. This new DirectContainer will facilitate the auto-creation of triples that will define the membership relationship between the book, "raven/", and the proxies. Then, the new proxy resources within this DirectContainer will be used to establish an ordering of the books pages.
Note: This example assumes the previous creation of "/objects/raven/" and the cover and page resources from the Book example in this series.
curl -i -XPUT -H"Content-Type: text/turtle" --data-binary @ldp-ordering-direct.ttl localhost:8080/rest/objects/raven/orderProxies/
Where "ldp-ordering-direct.ttl" follows:
@prefix ldp: <http://www.w3.org/ns/ldp#> @prefix pcdm: <http://pcdm.org/models#> @prefix ore: <http://www.openarchives.org/ore/terms/> <> a ldp:DirectContainer, pcdm:Object ; ldp:membershipResource </rest/objects/raven/> ; ldp:isMemberOfRelation ore:proxyIn .
An ldp:DirectContaner is an LDP construct that activates the creation of certain RDF triples when a new resource is added as a child of this container.
Like the "pages/" DirectContainer in an earlier example, the "orderProxies/" includes the ldp:membershipResource property ("raven/"). However, it is important to point out that the "orderProxies/" DirectContainer *does not* have the ldp:hasMemberRelation property defined, but instead uses ldp:isMemberOfRelation of "ore:proxyIn".
By using ldp:isMemberOfRelation, the auto-created triple resulting from the addition of a new child resource within "orderProxies/" will take the form:
<new-resource> <ore:proxyIn> <http://localhost:8080/rest/objects/raven/>
We will see this in action next!
Create a new pcdm:Object, "coverProxy/", that is also an ldp:RdfSource within the "orderProxies/" DirectContainer.
curl -i -XPUT -H"Content-Type: text/turtle" --data-binary @ldp-cover-proxy.ttl localhost:8080/rest/objects/raven/orderProxies/coverProxy
Where "ldp-cover-proxy.ttl" follows:
@prefix pcdm: <http://pcdm.org/models#> @prefix ore: <http://www.openarchives.org/ore/terms/> <> a pcdm:Object ; ore:proxyFor </rest/objects/raven/pages/cover> .
As described in the previous step, the addition of "coverProxy" automatically creates the following new triple on "coverProxy"
<http://localhost:8080/rest/objects/raven/orderProxies/coverProxy> ore:proxyIn <http://localhost:8080/rest/objects/raven>
Restating from the previous step,
- the subject of the triple is the new resource ("coverProxy") that was added to the ldp:DirectContainer ("orderProxies/")
- the predicate of the triple comes from the "ldp:isMemberOfRelation" defined on "orderProxies/", and
- the object of the triple comes from the "ldp:membershipResource" defined on "orderProxies/"
