Comunica Expression Evaluator

Previously called sparqlee - sparql expression evaluator. A simple spec-compliant SPARQL 1.1 expression evaluator package.

Learn more about the expression evaluator.

This module is part of the Comunica framework, and should only be used by developers that want to build their own query engine.

Click here if you just want to query with Comunica.

Install

$ yarn add @comunica/utils-expression-evaluator
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Exposed classes

• ExpressionEvaluator: An evaluator for SPARQL expressions working with Promises.
• IAsyncEvaluatorContext: Context used to configure the ExpressionEvaluator. See Config.
• SyncEvaluator: An evaluator for SPARQL expressions working without Promises.
• ISyncEvaluatorContext: Context used to configure the SyncEvaluator. See Config.
• AggregateEvaluator: An evaluator for SPARQL aggregate expressions working without promises. See Aggregates.
• ExpressionError: An error class for SPARQL expression errors as defined in the error section.
• isExpressionError: A way to check if an error is of type ExpressionError.
• orderTypes: A function to order types according to the SPARQL ORDER BY specification.
• AsyncAggregateEvaluator: An evaluator for SPARQL aggregate expressions working with promises. See Aggregates.

Development

Setup locally

1. Install yarn and node.
2. Run yarn install.
3. Use these evident commands (or check package.json):
   • building once: yarn run build

Layout and control flow

SPARQL Algebra expression can be transformed to an internal representation (see AlgebraTransformer.ts). This will build objects (see expressions module) that contain all the logic and data for evaluation. After transformation, the evaluator will recursively evaluate all the expressions.

Testing

The testing environment is set up to do a lot of tests with little code. The files responsible for fluent behaviour reside in the test/util module. Most tests can be run by running the runTestTable method in utils. This method expects a TestTable. Multiple test are run over a TestTable (one for every line). A TestTable may contain aliases if the aliases are also provided (Some handy aliases reside in Aliases.ts). This means that when testing something like "3"^^xsd:integer equals "3"^^xsd:integer is "true"^^xsd:boolean. We would write a small table (for this example some more tests are added) and test it like this:

import { bool, merge, numeric } from './util/Aliases';
import { Notation } from './util/TruthTable';
import { runTestTable } from './util/utils';
runTestTable({
  testTable: `
       3i 3i = true
       3i -5i = false
       -0f 0f = true
       NaN  NaN = false
   `,
  arity: 2,
  operation: '=',
  aliases: merge(numeric, bool),
  notation: Notation.Infix,
});
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More options can be provided and are explained with the type definition of the argument of runTestTable.

We can also provide an errorTable to the runTestTable method. This is used when we want to test if calling certain functions on certain arguments throws the error we want. An example is testing whether Unknown named operator error is thrown when we don't provide the implementation for an extension function.

import { bool, merge, numeric } from './util/Aliases';
import { Notation } from './util/TruthTable';
import { runTestTable } from './util/utils';
runTestTable({
  errorTable: `
       3i 3i = 'Unknown named operator'
       3i -5i = 'Unknown named operator'
       -0f 0f = 'Unknown named operator'
       NaN  NaN = 'Unknown named operator'
   `,
  arity: 2,
  operation: '<https://example.org/functions#equal>',
  aliases: merge(numeric, bool),
  notation: Notation.Infix,
});
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When you don't care what the error is, you can just test for ''.

In case the tables are too restrictive for your test, and you need an evaluation. You should still use the generalEvaluate function from generalEvaluation.ts. This function will automatically run both async and sync when possible. This increases your tests' coverage.