- From: Andy Seaborne <andy.seaborne@epimorphics.com>
- Date: Tue, 11 Oct 2011 13:47:56 +0100
- To: RDF-WG <public-rdf-wg@w3.org>
This is a quick sketch of how an application that requires quite detailed information about a g-box might go about it to illustrate the idea of dataset patterns. I'm sorry this is a bit rushed and a bit late. Andy ==== Time-varying g-boxes This is a Dataset Usage Pattern for recording the state of a resource [AWWW], where accessing the resource using HTTP GET results in receiving an RDF graph. The state of the resource is expected to change over time. The application wishes to have a record of the state of the resources at various times (it does not wish to just have a copy of the latest observed state). Each time a resource is accessed a new graph is added to the dataset as named graph. The URI in the (URI, Graph) pair for the named graph is a unique identifier created as part of the process of accessing the resource. The identifier is a URI and is never reused. The identifier is not the URL of the resource. Multiple resources can be tracked in the same dataset. Typically the identifier is a non-dereferencable URI such as a "tag:" or a "urn:uuid:". URIs in these scheme can be allocated cheaply and locally but guaranteed to be globally unique. A description of the action that resulted in the triples is recorded. In the example below it is stored in the default graph of the dataset, using the default graph as a manifest for the named graphs in the rest of the dataset. == Example 1 The resource <http://faraway/place> is read and returns a graph of one triple "<s> <p> <o>". The dataset management process allocates URI <tag:store,2010:1234> for the g-snap and <tag:store,2010:9876> for the interaction. ["allocates...for" is intentionally weak wording to not require normative meaning to the dataset named graph pair as that would obstruct other dataset usage patterns.] The dataset is modified as follows by adding: # Record the gSnap: <tag:store,2010:1234> { <s> <p> <o> } # Record the information about the operation performed { <tag:process,2010:9876> :valueObserved <tag:store,2010:1234> ; :actionTimestamp "2011-10-10T17:35:56Z"^^xsd:dateTime ; :gBoxLocation <http://faraway/place> } == Example 2 Later, the process reads the resource again, using a condition GET and is told the resource has not changed. The dataset management process generates a URI for the process step <tag:store,2010:ABCD> and links to the previous named graph because the graph value is the same. { <tag:process,2010:ABCD> :valueObserved <tag:store,2010:1234> ; :actionTimestamp "2011-10-11T09:35:56Z"^^xsd:dateTime ; :gBoxLocation <http://faraway/place> } == Discussion: The modelling is merely illustrative. In the examples, the action description triples go into the default graph. There is no necessary requirement for this. They could be stored in a designated system graph. They could be stored in a separate graph, not in the dataset or even in an associated dataset description with details such as a VoID details of the remote location. What the dataset is providing is the ability to query access the different observed g-snaps of the g-box.
Received on Tuesday, 11 October 2011 12:48:29 UTC