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Apache Marmotta - Linked Data Client

Linked Data Client

The Apache Marmotta LDClient library is a flexible and modular Linked Data Client (RDFizer) that can be used by any Linked Data project independent of the Apache Marmotta platform. In other words, it provides the infrastructure for retrieving remote resources via different protocols (primarily HTTP) and offers pluggable adapters (called “data providers”) that wrap other data sources (e.g. YouTube or Facebook) as Linked Data resources by mapping their data to appropriate RDF structures.

Core Libraries

The following libraries are core libraries for using LDClient:

  • ldclient-api: provides model and interfaces for using LDClient
  • ldclient-core: provides the core infrastructure for accessing Linked Data Resources

Note that the core libraries will not provide any functionality without at least one of the backends (typically you would at least include the RDF backend for accessing ordinary Linked Data resources).

Backends

Apache Marmotta already includes a number of different backends that provide access to various kinds of online resources. How they produce RDF in detail is described in modules.

  • ldclient-provider-rdf: provides access to any resources conforming to the Linked Data principles, i.e. returns data in one of the RDF formats (RDF/XML, Turtle, N3, JSON-LD)
  • ldclient-provider-xml: an abstract backend serving as a base for any XML-based data source; offers a model for mapping XPath statements to RDF property values (used e.g. by the YouTube backend)
  • ldclient-provider-html: an abstract backend serving as a base for any HTML-based data source; offers a model for mapping jQuery-like CSS selectors to RDF property values (using JSoup)
  • ldclient-provider-freebase: enables the access to data from Freebase via its API and doing some fixing in the serialization format (experimental).
  • ldclient-provider-facebook: enables the access the metadata of Facebook objects using the Facebook Graph API, and maps them using FOAF, SIOC, SKOS or schema.org (experimental).
  • ldclient-provider-youtube: allows accessing YouTube resources (videos, playlists, channels) as if they were proper Linked Data resources; maps properties to the Ontology for Media Resources
  • ldclient-provider-vimeo: allows accessing Vimeo resources (videos and channels) as if they were proper Linked Data resources; maps properties to the Ontology for Media Resources
  • ldclient-provider-rdfa: accesses HTML pages augmented with RDFa and retrieves the RDF data contained in the page
  • ldclient-provider-mediawiki: accesses wiki articles via the API of MediaWiki installations and maps the metadata to the SIOC and FOAF vocabularies
  • ldclient-provider-phpbb: accesses the posts in a PHPBB forum and maps them to the SIOC vocabulary (experimental)
  • ldclient-provider-ldap: accesses users in a LDAP directory and maps them to the FOAF vocabulary (experimental)