Add RDF module

[mhrimaz]

Bring back the RDF module.

I used commit 3e5f53c as a base.

Steps to get a running version first and at least produce some valid JSON-LD serializations:

• update @JsonProperty to new namespace
• LangString defined as AbstractLangString and divided into different sub classes specific for each element
• Certain classes renamed such as DataSpecificationIEC61360 to DataSpecificationIec61360

Old code evaluation:

• Parser logic uses SPARQL query to parse which is wrong approach.
• Serializer uses Jackson to convert to JSON-LD and then Apache Jena parse the JSON-LD to construct a Model and then it will serialize RDF/Turtle. The workflow is inefficient. Mixins are simply repeated and at the end Jackson as an extra dependency doesn't add any value other than unnecessary complexity.

Next steps are:

• Rewrite the whole structure of Serializer and Parser with no dependency on Jackson.
• Increase test case coverage and include invalid scenarios with proper exception handling and logging.
• Refactoring internal structure and decide about public API
• Decide on how to handle order relevant elements and write a decision-record for it.
• Apply necessary changes with respect to v3.1

Features (?):

• Support for identifier templating https://www.w3.org/2001/sw/rdb2rdf/r2rml/#from-template
• Triplestore utility
• Visualization utility

Last update: 08.02.2024

[twebermartins]

Thank you very much for your contribution! We will have a look at it!

[mjacoby]

Since RDF de-/serialization is not yet officially standardized we will not merge this but leave it as a draft so others who are interested in using ti can easily find it.