SPARQL2NEMO Converter

Transforms a given SPARQL query to Nemo code. The program works by transforming operations of the SPARQL algebra recursively. Translation to SPARQL algebra uses spargebra which is developed as part of the Oxigraph graph database.

Supported Features

Translation implementations for SPARQL Features can be found in translation.rs. A German explanation how the Translation works is included in the Repository. Functions are generally named after the SPARQL algebra operation they translate.

There are special suffixes for functions that do not produce solution sets:

• *_seq for solution sequence: first position of resulting predicate is index in solution sequence
• *_multi for solution multiset (a.k.a. unordered solution sequence): first position of resulting predicate is multiplicity
• *_g for generic implementations supporting multiple types of solutions
• *_multi_g for generic implementations supporting solution multiset and regular solution sets
• *_seq_g for generic implementations supporting solution sequences and regular solutions sets

You may also look at the example queries in tests.rs.

Known differences to SPARQL 1.1 Query standard

• No support for FROM clause and other graph management features
• No support for using variables in an EXISTS expression that are only defined outside the EXISTS expression
• Empty In-expression can error e.g. 0/0 in () evaluates to an error but should be false
• DISTINCT and REDUCED do not preserve orders previously given by ORDER BY
• In some cases an incorrect type of equality is used - explicit equality checking and graph pattern matching should work correctly
• GROUP BY does not support grouping by all variables simultaneously
• Some symbols in variable names may be not supported
• Literals may not be handled completely in line with SPARQL
  • Nemo applies some normalization to literals which may change results in some cases, there are no malformed literals
  • Nemo does not apply numeric type promotion and subtype substitution rules from SPARQL
  • Function and operators may not have standard compliant input/output types
  • Only minimal support for xsd:decimal
  • Only minimal support for language tagged strings
• Some functions and aggregations are not implemented
• Comparisons do not work for Datetime values
• Some Nemo functions are not Standard compliant e.g. Nemo uses a simpler regex syntax

Usage

There is no explicit UI. The output NEMO program is printed to stdout and needs to be combined with the graph data and executed manually. The input graph is currently provided in NEMO as the ternary predicate input_graph(?subject, ?predicate, ?object).

Select a mode by calling the desired function in main():

• _test_translation(): Converts a SPARQL query (supplied as query_str) to NEMO program
• _test_parsing(): Converts a SPARQL query (query_str) to SPARQL algebra
• _test_rust(): For trying out some Rust features
• _test_model(): For trying out the Rust macro based NEMO templating language
• _translate_stdin(): For reading SPARQL query from stdin printing NEMO translation to stdout

Run the code using:

cargo +nightly run

You may need to install the following packages if you don't have them already (Ubuntu):

sudo apt update
sudo apt install pkg-config
sudo apt install libssl-dev

Tests need to be run with RUST_TEST_THREADS=1 environment variable because Nemo uses timing locks where it is unknown how multithreading is supported with this.

Note that this code works with an old version of Nemo

Translate queries from stdin

• Ensure the _translate_stdin() function is called in main.
• Build using cargo +nightly build --release
• Use using echo "ASK {?a ?b ?c}" | ./target/release/sparql2nemo
• Translation is written to stdout