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Working with YARRRML

YARRRML (.yarrrml, .yarrrml.yml, .yarrrml.yaml) is a human-friendly, declarative YAML syntax for defining rules that map raw data sources (like CSV, JSON, or databases) into RDF triples. Instead of writing complex RML/R2RML schemas directly, you write simple YAML rules. neonto editor extends standard YAML editing with rich, YARRRML-aware auto-completion, hover definitions, syntax diagnostics, and refactoring utilities.

Authoring a mapping​

A typical YARRRML file defines prefixes, points to data sources, and maps columns or keys to RDF subjects (s) and predicate-object (po) pairs:

prefixes:
    ex: "http://example.org/"
    foaf: "http://xmlns.com/foaf/0.1/"

mappings:
    person:
        sources:
            - [ "people.csv~csv" ]
        s: ex:$(id)
        po:
            - [ a, foaf:Person ]
            - [ foaf:name, $(name) ]

Autocomplete​

A .yarrrml mapping with the completion popup open after typing "function: grel", listing transform functions with documentation for sha1 shown alongside

Figure 1. Transform functions can be autocompleted directly into the mapping block.

Press Ctrl+Space in a YARRRML file to get completions for:

  • YARRRML structure: Core keys like mappings, sources, s / subject, po / predicateobjects, p / predicate, o / object, datatype, language, and prefixes.
  • Prefixes: Namespaces declared in the file or available in your workspace.
  • Transformation functions: Built-in functions from the Function Ontology (FnO), including string splits, math functions, and hash generators. neonto inserts them as YAML blocks with parameter placeholders.

Function completion settings​

Change how neonto inserts function templates in VS Code Settings (Ctrl+,):

SettingDefaultDescription
neonto.ingestion.functionPlaceholder"Todo - Add Input Value"The text used as a placeholder for a function's parameters.
neonto.ingestion.abbreviatedFunctionParametersfalseIf enabled, inserts parameter names using short keys rather than full URIs.

Hover documentation​

Hover over a vocabulary prefix, FnO function name, or mapping construct to inspect its documentation, parameters, or full namespace URI. See Working with Turtle to control labels and languages.

Live diagnostics​

neonto analyzes mapping rules as you edit. It flags indentation issues, missing keys, invalid paths, and syntax errors. The editor highlights these issues and lists them in the Problems panel (Ctrl+Shift+M).

A .yarrrml file with a diagnostic squiggle under predicateobjects and the Problems panel reporting "After the predicateobjects (po), only predicates (p) or objects (o) can follow"

Figure 2. Live syntax diagnostics show immediately in the editor and in the Problems panel.

Refactoring and utilities​

Prefix substitution​

Replace full, expanded URIs as follows:

  1. Open the Command Palette (Ctrl+Shift+P or F1).
  2. Run neonto: Replace the full URIs with the prefixes in the file.
  3. Any expanded URIs matching declared prefixes are rewritten into their compact prefixed form.

Browsing available functions​

To browse available data transform functions and their arguments:

  1. Run neonto: Display the function ontology (FnO) from the Command Palette.
  2. A Turtle document opens beside your editor. It describes each supported function, including GREL (General Refine Expression Language) transformations, math helpers, and crypto functions.

The function ontology opened as a Turtle document, describing the GREL FnO descriptions dataset and its transform functions

Figure 3. The function ontology (FnO) reference document.