GraphDB version is packaged as a Storage and Inference Layer (SAIL) for Sesame version 2.x and makes extensive use of the features and infrastructure of Sesame, especially the RDF model, RDF parsers and query engines. Inference is performed at load time, where the explicit and inferred statements are stored in highly-optimised data structures. The inferred closure is updated through inference at the end of each transaction that modifies the repository.
GraphDB implements the Sesame SAIL interface, so that it can be integrated with the rest of the Sesame framework, e.g. the query engines and the web user interface tools. A typical user application uses GraphDB directly through the Sesame SAIL API. When a GraphDB repository is exposed using the Sesame HTTP Server, users can manage the repository through the Sesame Workbench Web application, or with other tools that can integrate with Sesame, e.g. ontology editors like TopBraid Composer.
However, GraphDB-SE can also be used with the Jena framework, which is achieved with a customised Jena/Sesame/GraphDB-SE adapter component.
Sesame comprises a large collection of libraries, utilities and APIs, but the important components for this section are:
This section describes using the Sesame API to create and access GraphDB repositories, both on the local file-system and remotely via the Sesame HTTP server, plus a brief introduction is given to the Sesame workbench Web application, which provides many repository management functions through a convenient user interface. This is followed by information on using GraphDB-SE with Jena and some related components, i.e. ARQ and Joseki.
Programmatically, GraphDB is used via the Sesame Java framework of classes and interfaces. Documentation for these interfaces (including Javadoc) can be found at http://www.openrdf.org. Code snippets in the following sections are taken from (or are variations of) the GettingStarted example program that comes with the GraphDB distribution.
With Sesame 2, repository configurations are represented as RDF graphs. A particular repository configuration is described as a resource, possibly a blank node, of type: http://www.openrdf.org/config/repository#Repository.
The Java code to use the configuration to instantiate a repository and get a connection to it is as follows: Note that the code to parse this file and find the 'root' node for the configuration can be found in the getting-started program.
The procedure is as follows: instantiate a local repository manager with the data directory to use for the repository storage files (repositories will store their data in their own sub-directory from here), add a repository configuration for the desired repository type to the manager, 'get' the repository and open a connection to it. From then on, most activities will use the connection object to interact with the repository, e.g. executing queries, adding statements, committing transactions, counting statements, etc. See the getting-started application for examples.
The Sesame Server is a Web application that allows interaction with repositories using the HTTP protocol. It runs in a JEE compliant servlet container, e.g. Tomcat, and allows client applications to interact with repositories located on remote machines. All that is required to connect to and use a remote repository instead of a local one, is to replace the local repository manager for a remote one. The URL of the Sesame Server must be provided, but no repository configuration is needed if the repository already exists on the server. The following lines can be added to the getting-started example program, although a correct URL must be specified:The rest of the example program should work as expected, although the following library files must be added to the class-path:
The installation section explains how to set up a GraphDB repository that is exposed via the Sesame HTTP Server. In summary, the Sesame Server and Workbench applications are deployed to a Tomcat instance and the necessary library files (GraphDB, Lucene, etc) are copied to the correct locations. After this, the Sesame console application is used with the owlim.ttl repository template file to connect to the Sesame server and create a repository instance.
The server has a simple user interface that shows status, logging and configuration information.
The workbench lists repositories and their namespaces, allows for the addition and deletion of statements, and provides a query interface for SPARQL and SeRQL query languages. However, the list of repository types is currently hard-coded in the workbench, so a GraphDB repository must still be created using the Sesame console application, as described in the installation section.
The Sesame HTTP server is a fully fledged SPARQL endpoint - the Sesame HTTP protocol is a super-set of the SPARQL 1.1 protocol - that provides an interface for transmitting SPARQL queries and updates to a SPARQL processing service and returning the results via HTTP to the entity that requested them.
Any tools or utilities designed to interoperate with the SPARQL protocol will function with GraphDB when deployed using the Sesame HTTP server, i.e. the openrdf-sesame Web application.
T1he SPARQL 1.1 Graph Store HTTP Protocol is fully supported for direct and indirect graph names. The W3C working draft has the most details, although further information can be found in the Sesame user guide.
This protocol supports the management of RDF statements in named graphs in the REST style, by providing the ability to get, delete, add to or overwrite statement in named graphs using the basic HTTP methods.
Jena is a Java framework for building Semantic Web applications. It provides a programmatic environment for RDF, RDFS, OWL and SPARQL and includes a rule-based inference engine. Access to GraphDB-SE via the Jena framework is achieved with a special adapter, which is essentially an implementation of the Jena ARQ interface that provides access to individual triples managed by a GraphDB-SE repository through the Sesame API interfaces.
The Jena adapter for GraphDB-SE is not a general purpose Sesame adapter and cannot be used to access any Sesame compatible repository, because it utilises an internal GraphDB-SE API to provide more efficient methods for processing RDF data and evaluating queries.
The adapter comes with its own implementation of a Jena 'assembler' factory to make it easier to instantiate and use with those related parts of the Jena framework, although one can instantiate an adapter directly by providing an instance of a Sesame SailRepository (a GraphDB-SE GraphDBRepository implementation). Query evaluation is controlled by the ARQ engine, but specific parts of a Query (mostly batches of statement patterns) are evaluated natively through a modified StageGenerator plugged into the Jena runtime framework for efficiency. This also avoids unnecessary cross-API data transformations during query evaluation.
The Jena adapter can be used as follows, where a 'repositoryConnection' is obtained as in the example in the Sesame section above:From now on the SesameDataset object can be used through the Jena API as regular Dataset, e.g. to add some data to it one could do something like the following: The performance of GraphDB-SE when used through Jena is quite similar to using it through the Sesame APIs. For most of the scenarios and tasks GraphDB-SE can deliver considerable performance improvements when used as a replacement for Jena's own native RDF backend TDB. More information is provided on the GraphDB through Jena Performance page.
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