Support language-tagged literals from DataFrame columns in template mapping

[henrieglesorotos]

Static Literal objects with language tags work correctly in template instances as far as I can see

  static_label = Literal('Static Label', language='en')
  Triple(subject, predicate, static_label)  # -> Produces "Static Label"@en

However, there's no way to produce language-tagged literals for dynamic values from DataFrame columns.

What works:

Static literal in template - produces "Static"@en

Triple(subject, predicate, Literal('Static', language='en'))

What doesn't work:

1. Literal objects in DataFrame:

df = pl.DataFrame({'label': [Literal('Dynamic', language='en')]})
Result: MaplibException: Datatype error 'Unknown datatype Binary'

2. RDFType.Literal with language parameter:

Parameter(variable=label_var, rdf_type=RDFType.Literal(language='en'))
Result: TypeError: RDFType.Literal() got an unexpected keyword argument 'language'

I might be doing something really stupid? 😭

Environment:

• maplib version: 0.18.13
• Python: 3.13

[magbak]

Hi! Good question, this functionality is not exactly very accessible today, we have to have a struct-column with very particular column names. See more on structs here.
It should be possible to specify this statically for all values in a column, I agree. Will probably do this as you suggest.
Also we should not have to use the very cryptic column names used below. I propose: "value" and "language" inside the struct as fields. Let me know what you think, and I will get back.

df = pl.DataFrame({
    "id":["urn:ex:a", "urn:ex:b"],
     "value":["abc", "def"],
     "lang": ["en", "fr"]
})

df = df.with_columns(
    pl.struct([
        pl.col("value").alias("<http://www.w3.org/1999/02/22-rdf-syntax-ns#langString>"),
        pl.col("lang").alias("l")]
    ).alias("my_lang_col"))
m = Model()
tmpl = m.map_default(df.select("id", "my_lang_col"), "id")
df_res = m.query("SELECT * WHERE {?a ?b ?c}")
print(tmpl)
print(df_res)

Produces:

@prefix def: <urn:maplib_default:> .
@prefix ottr: <http://ns.ottr.xyz/0.4/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

def:default_template_0 [
     ottr:IRI ?id, 
     rdf:langString ?my_lang_col ] :: {
  ottr:Triple(?id, def:my_lang_col, ?my_lang_col)
} . 


shape: (2, 3)
┌────────────┬─────────────────────────────────┬──────────┐
│ a          ┆ b                               ┆ c        │
│ ---        ┆ ---                             ┆ ---      │
│ str        ┆ str                             ┆ str      │
╞════════════╪═════════════════════════════════╪══════════╡
│ <urn:ex:a> ┆ <urn:maplib_default:my_lang_co… ┆ "abc"@en │
│ <urn:ex:b> ┆ <urn:maplib_default:my_lang_co… ┆ "def"@fr │
└────────────┴─────────────────────────────────┴──────────┘

[henrieglesorotos]

Gotcha, thank you. That makes sense. I can use the defined keys in a struct for now. Not sure about this one exactly, but I'm happy to contribute going forward. Is there a contribution guide?

[magbak]

We will get back with a contribution guide in not too long!