CommandExecutor for external CLI tools as pipeline steps

[ddeboer]

Summary

Add a CommandExecutor that runs an external CLI command as a pipeline step, reading quads from stdin or a file and producing quads (or other output) on stdout or to a file.

Context

Some pipeline steps are best handled by external tools rather than in-process Node.js code. For example, loda-pipeline's post-processing chain:

1. Deduplication — Jena's sparql CLI running a CONSTRUCT query against an N-Triples file
2. SHACL validation — Jena's shacl validate against EDM shapes
3. Format conversion — Jena's riot --output=rdfxml for N-Triples → RDF/XML
4. EDM XML packaging — a custom Java tool (Rdf2EdmCl) that splits RDF/XML into individual EDM XML files in a ZIP

These don't fit the SPARQL CONSTRUCT executor model — they're file-in, file-out CLI invocations. A CommandExecutor would make them composable as pipeline steps.

Approach

A CommandExecutor implements the same interface as SparqlConstructExecutor but delegates to an external process:

class CommandExecutor implements Executor {
  constructor(options: {
    command: string;       // e.g. 'riot'
    args: string[];        // e.g. ['--output=rdfxml']
    // How to pass input: stdin pipe, file path substitution, or no input
    input?: 'stdin' | 'file';
    // How to read output: stdout pipe or file path
    output?: 'stdout' | 'file';
  });
}

This is also the pattern proposed for SparqlAnythingExecutor in the design doc — spawning java -jar sparql-anything.jar per query, parsing N-Triples from stdout.

Uses @lde/task-runner for process lifecycle management (Docker or host execution).

Subsumes #18

SparqlAnythingExecutor is a specialised CommandExecutor — it spawns java -jar sparql-anything.jar and parses N-Triples from stdout. Rather than building a one-off executor for SPARQL Anything, the generic CommandExecutor covers it and any other CLI tool.

Relates to

• Data Pipelines Framework #78
• SPARQL Anything for non-RDF origin data #18 (SPARQL Anything — a specific case of CommandExecutor)