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• API logic in a singleLinked Data Templates ontology
• control of RDF input quality with SPARQL-based constraints
• SPARQL endpoint and Graph Store Protocol endpoint
• HTTP content negotiation and caching support

AtomGraph's direct use of semantic technologies results in extemely extensible and flexible design and leads the way towards declarative Web development. You can forget all about broken hyperlinks and concentrate on building great apps on quality data. For more details, seearticles and presentations about AtomGraph.

For a compatible frontend framework for end-user applications, seeAtomGraph Web-Client.

• how AtomGraph Processor works
• Linked Data Templates
• installing AtomGraph Processor

For full documentation, see thewiki index.

Processor is available from Docker Hub asatomgraph/processor image.It accepts the following environment variables (that become webapp context parameters):

ENDPOINT

SPARQL 1.1 Protocol endpoint

URI

GRAPH_STORE

SPARQL 1.1 Graph Store Protocol endpoint

URI

ONTOLOGY

Linked Data Templates ontology

URI

AUTH_USER

SPARQL service HTTP Basic auth username

string, optional

AUTH_PWD

SPARQL service HTTP Basic auth password

string, optional

PREEMPTIVE_AUTH

use premptive HTTP Basic auth?

true/false, optional

If you want to have your ontologies read from a local file rather than their URIs, you can define a customlocation mapping that will be appended to the system location mapping.The mapping has to be a file in N3 format and mounted to the/usr/local/tomcat/webapps/ROOT/WEB-INF/classes/custom-mapping.n3 path. Validate the file syntax beforehand to avoid errors.

To enable logging, mountlog4j.properties file to/usr/local/tomcat/webapps/ROOT/WEB-INF/classes/log4j.properties.

The examples show Processor running with combinations of

• default and custom LDT ontologies
• local and remote SPARQL services
• Docker commands

However different combinations are supported as well.

TheFuseki example shows how to run a localFuseki SPARQL service together with Processor and how to setupnginx as a reverse proxy in front of Processor. Fuseki loads RDF dataset from a file. Processor uses a built-in LDT ontology.It uses thedocker-compose command.

Run the Processor container together withFuseki andnginx container:

cd examples/fusekidocker-compose up

After that, open one of the following URLs in the browser and you will retrieve RDF descriptions:

• http://localhost:8080/ - root resource
• http://localhost/ - root resource where the hostname of the Processor's base URI is rewritten toexample.org

Alternatively you can runcurl http://localhost:8080/ etc. from shell.

In this setup Processor is also available onhttp://localhost/ which is the nginx host.The internal hostname rewriting is done by nginx and useful in situations when the Processor hostname is different from the application's dataset base URI and SPARQL queries do not match any triples.Thedataset for this example contains a secondhttp://example.org/ base URI, which works with the rewrittenexample.org hostname.

TheWikidata example example shows to run Processor with a custom LDT ontology and a remote SPARQL service.It uses thedocker run command.

Run the Processor container with the Wikidata example:

cd examples/wikidatadocker-compose up

After that, open one of the following URLs in the browser and you will retrieve RDF descriptions:

• http://localhost:8080/ - root resource
• http://localhost:8080/birthdays - 100 people born today
• http://localhost:8080/birthdays?sex=http%3A%2F%2Fwww.wikidata.org%2Fentity%2FQ6581072 - 100 females born today
• http://localhost:8080/birthdays?sex=http%3A%2F%2Fwww.wikidata.org%2Fentity%2FQ6581097 - 100 males born today

Alternatively you can runcurl http://localhost:8080/ etc. from shell.

Note that Wikidata's SPARQL endpointhttps://query.wikidata.org/bigdata/namespace/wdq/sparql is very popular and therefore often overloaded. An error response received by the SPARQL client from Wikidata will result in500 Internal Server Error response by the Processor.

Processor is released on Maven central ascom.atomgraph:processor.

AtomGraph Processor doesnot include an RDF datasource. It queries RDF data on the fly from a SPARQL endpoint usingSPARQL 1.1 Protocol over HTTP. SPARQL endpoints are provided by most RDFtriplestores.

The easiest way to set up a SPARQL endpoint on an RDF dataset is Apache JenaFuseki as a Docker container using ourfuseki image. There is also a number of ofpublic SPARQL endpoints.

For a commercial triplestore with SPARQL 1.1 support seeDydra.

Processor includes a basic HTTPtest suite for Linked Data Templates, SPARQL Protocol and the Graph Store Protocol.

Pleasereport issues if you've encountered a bug or have a feature request.

Commercial consulting, development, and support are available fromAtomGraph.

Please join the W3CDeclarative Linked Data Apps Community Group to discussand develop AtomGraph and declarative Linked Data architecture in general.