Скачать или смотреть Solving the Double Data Type Issue in Apache Jena for RDF Star Queries

Discover how to overcome the issue of `double data type` not functioning correctly with RDF Star queries in Apache Jena. Learn about solutions and recommendations.
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This video is based on the question https://stackoverflow.com/q/67759806/ asked by the user 'penguin2048' ( https://stackoverflow.com/u/5695235/ ) and on the answer https://stackoverflow.com/a/67763876/ provided by the user 'AndyS' ( https://stackoverflow.com/u/757100/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: RDF Star and Double Data Types

If you’re working with Apache Jena and have encountered issues when querying RDF Star triples that include a double data type, you're not alone. Many developers have faced a similar problem, especially when using Jena version 3.17. Let's walk through this issue to understand it better and find a solution.

The Issue

When attempting to execute a query with RDF Star data that incorporates xsd:double, the query fails to return results. Developers find that replacing the double type with either an xsd:float or xsd:decimal resolves the problem, leading to confusion about the underlying cause.

The use of RDF Star introduces complexities related to data types and indexing, which can lead to unexpected behaviors. Here’s a brief overview of a code snippet that demonstrates this problem:

[[See Video to Reveal this Text or Code Snippet]]

When querying the inserted data using:

[[See Video to Reveal this Text or Code Snippet]]

The result set yields no data, even though other numeric types work.

Finding the Solution

Upgrading to Jena 4.0.0

The most effective remedy to this issue is to upgrade your version of Apache Jena from 3.17 to 4.0.0 or later. The upgrade addresses several issues related to SPARQL querying, especially pertaining to how triples are indexed and handled.

Why This Works

Changes in Indexing: In version 3.17.0, SPARQL's indexing methods are less advanced, making it problematic to handle RDF Star triples with xsd:double. Jena 4.0.0 introduced improvements to better manage these types.

Non-canonical Terms: The earlier versions may have had problems with how non-canonical terms were mapped, directly impacting data retrieval when specific data types are involved.

Alternative Approaches

If upgrading is not an immediate option, there are a few workarounds you might consider:

Use Lexical Forms: Instead of using the direct representation, try using a lexical form such as "1.0e0"^^xsd:double. This may provide better consistency across different data types.

Experiment with Other Data Types: If feasible, consider using xsd:float or xsd:decimal temporarily while you prepare for any necessary changes to your codebase.

Conclusion

In summary, if you're facing issues with using double data types in RDF Star queries in Apache Jena, the most straightforward approach is to upgrade to version 4.0.0. This change will significantly enhance your ability to handle complex data types and optimize the querying of RDF Star data.

Feel free to share your experiences or any additional tips that worked for you in the comments below!