Connecting to Other Stores¶
BrightstarDB provides a set of high-level APIs for working with RDF data that we think are useful regardless of what underlying store you used to manage the RDF data. For that reason we have done some work to enable the use of the Data Object Layer, Dynamic API and Entity Framework with stores other than BrightstarDB.
If your store provides SPARQL 1.1 query and update endpoints that implement the SPARQL 1.1 protocol specification you can use a SPARQL connection string. For other stores you can use DotNetRDF’s configuration syntax to configure a connection to the store.
To use this functionality in BrightstarDB, the store must support query using SPARQL 1.1 Query and update using SPARQL 1.1 Update. The store must also have a connector available for it in DotNetRDF, or support SPARQL 1.1 Protocol.
A number of commercial and non-commercial stores are supported by DotNetRDF (for a list please refer to the DotNetRDF documentation).
Configuration and Connection Strings¶
The connection to your store must be configured by providing an RDF file that contains the configuration information. We use the DotNetRDF Configuration API and load the configuration from a file whose path you specify in the connection string (refer to Connection Strings for more details).
In the DotNetRDF configuration file you need to either configure one or more Storage Providers or a single Storage Server (at the time of writing the configuration for these has not been documented in the DotNetRDF project).
Using Storage Providers¶
This approach provides a flexible way to make one or more RDF data stores accessible via the BrightstarDB APIs. You must create a DotNetRDF configuration file that contains the configuration for each of the stores you want to access. Each store must be configured as a DotNetRDF StorageProvider.
Each configuration you create should have a URI identifier assigned to it (so don’t use a blank node for the configuration in the configuration file). The full URI of the configuration resource is used as the store name in calls to DoesStoreExist() or OpenStore(). For a shorter store name it is also possible to use a relative URIs - these will be resolved against the base URI of the configuration graph.
The connection string you use for BrightstarDB is then just:
configuration_file_path is the full path to the DotNetRDF configuration file.
Using A StorageServer¶
DotNetRDF supports connections to Sesame and to Stardog servers that manage multiple stores. These connections must be configured as a DotNetRDF StorageServer. In this case, the list of stores is managed by the storage server so you don’t need to write a separate configuration for each individual store on the server.
The configuration you create must have a URI identifier assigned to it. The full URI of this configuration resource is used in the connection string.
The connection string you would use for BrightstarDB in this scenario follows this template:
config_file_path is the full path to the DotNetRDF configuration file, and
config_uri is the URI identifier of the configuration resource for the storage server.
Using SPARQL endpoints¶
If the data store you want to connect to supports SPARQL 1.1 Query and Update and the SPARQL 1.1 Protocol specification, then you can create a connection that will use the SPARQL query and update endpoints directly. The template for this type of connection string is:
query_endpoint_uri is the URI of the SPARQL query endpoint for the server and
update_endpoint_uri is the URI of the SPARQL update endpoint.
You can omit the
update= part of the connection string, in which case the connection
will be a read-only one and calls to
SaveChanges() will result in a runtime exception.
If credentials are required to access the server, these can be passed in using optional
Differences to BrightstarDB Connections¶
We have tried to keep the differences between using BrightstarDB and using another store through the high-level APIs to a minimum. However as there are many differences between different store implementations, so there are a few points of potential difference to be aware of:
- Default dataset and update graph.
If not overridden in code, the default dataset for a BrightstarDB connection is all graphs in the store; for another store the default dataset is defined by the server. Similarly if not overridden in code, the default graph for updates on a BrightstarDB connection is the BrightstarDB default graph (a graph with the URI
http://www.brightstardb.com/.well-known/model/defaultgraph); for another store, the default graph for updates is defined by the server.
To minimize confusion it is a good idea to always explicitly specify the update graph and default data set when your code may connect to stores other than BrightstarDB and to ensure that the update graph is included in the default data set.
- Optimistic locking
This is currently unsupported for connections to stores other than BrightstarDB as its implementation depends on functionality not available in SPARQL 1.1 protocol.
- Transactional Updating
This is highly dependent on the way in which the store’s SPARQL update implementation works. The code will send a set of SPARQL update commands in a single request to the store. If the store does not implement the processing such that the multiple updates are handled in a single transaction, then it will be possible to end up with partially completed updates. It is worth checking with the documentation for your store / endpoint to see what transactional guarantees it makes for SPARQL Update requests.
Connecting over SPARQL Protocol¶
DotNetRDF configuration file (dotNetRdf.config.ttl):
@prefix dnr: <http://www.dotnetrdf.org/configuration#> . @prefix : <http://example.org/configuration#> . :sparqlQuery a dnr:SparqlQueryEndpoint ; dnr:type "VDS.RDF.Query.SparqlRemoteEndpoint" ; dnr:queryEndpointUri <http://example.org/sparql> . :sparqlUpdate a dnr:SparqlUpdateEndpoint ; dnr:type "VDS.RDF.Update.SparqlRemoteUpdateEndpoint" ; dnr:updateEndpointUri <http://example.org/update> .
Connecting to a Fuseki Server¶
DotNetRDF configuration file (dotNetRdf.config.ttl):
@prefix dnr: <http://www.dotnetrdf.org/configuration#> @prefix : <http://example.org/configuration#> :fuseki a dnr:StorageProvider ; dnr:type "VDS.RDF.Storage.FusekiConnector" ; dnr:server "http://fuseki.example.org/dataset/data" .
- connection string::
TBD: More examples