Metadata Graph Predicates
The Anzo system defines and makes use of several predicates of the NamedGraph ontology class for managing named graphs and dealing with them in the client APIs. These can be found (amongst other things) in the anzo.owl ontology.
http://www.openanzo.org/projects/openanzo/browser/branches/server_194_1617/anzo-common/docs/anzo.owl
The Anzo API will have a graph metadata object that exposes the above mentioned predicates for simple access.
However, different data sources and applications may have other predicates, and subclasses of NamedGraph that they need to define for tasks such as relating named graphs, storing richer provenance info than just the revision, etc...its really just a property bag associated with a graph. In particular non-anzo data sources require a place to store statements (note that the metadata graph associated with a graph need not be sourced from the same place the graph it describes is). These additional predicates may have their own ontologies and will probably not? be supported by the Anzo API's graph metadata object.
The purpose of this document is to begin compiling a list of the possible predicates required by data sources and applications, and eventually develop a set of potential ontologies.
Predicates may be required for the following:
FOR DISCUSSION & DEBATE
Some of these already exist in the ontology linked above.
A graph's System Metadata
Predicates one can always expect to find and that are directly supported by the API's graph metadata object as simple properties.
- ACL's (can I read, write, change ACL's)
- SourceReadOnly? (the ACL may make something readonly, but this lets the user know the source is ALWAYS readonly e.g. from a readonly store or the web)
- Notifications available
- Persistence level on server (revisioned, non-revisioned, non-persisted, federated)
- Revision info (this is not the same as provenance, but may be related)
- Creator and "last modified" info (who and when).
- SpecializedGraph? (Web service, Federated, ?)
- DataSource?
- List of specific Ontologies/RDFS supported
- AllowOffSchemaEntries? - can data be created that does not match schema above i.e. non-RDF backend
A graph's Non-system Metadata
Predicates that one might optionally expect to find, but that are not directly supported by the Anzo API's graph metdata object. Cardinality can be 0->n
- SeeAlso? - points to other graphs with the same/related resource(s?) to those in this graph
- ProvenanceAvailable? - link to any named graph/dataset which may have provenance for this graph
- MemberOfDataset? - name of dataset to which this graph is a member
- SemanticView? - name of SemanticView? of which this graph belongs
