Forward slash in JSON key treated as error

[jakubklimek]

A forward slash in JSON key like this:

{
  "@context": {
    "@version": 1.1,
    "a/b": "https://a"
  }
}

is treated as bad syntax: jsonld.SyntaxError: Invalid JSON-LD syntax; term in form of IRI must expand to definition.
However, forward slash is perfectly valid in JSON.
Where does this syntax error come from?

{
  "@context": {
    "@version": 1.1,
    "a_b": "https://a"
  }
}

is OK.

[jakubklimek]

However, Apache Jena riot also reports this as invalid:

ERROR org.apache.jena.riot - A local context contains a term that has an invalid or missing IRI mapping [code=INVALID_IRI_MAPPING].

when used like this:

{
  "@context": {
    "@version": 1.1,
    "a/b": "https://a"
  },
  "@id": "https://id",
  "a/b": 2
}

[lemoustachiste]

@jakubklimek your issue is not too far from the one I was having here: #542. Maybe it can help

[VladimirAlexiev]

@jakubklimek @lemoustachiste (and we got a similar issue at graphdb-support):

Forward slashes and colons are forbidden in JSON-LD terms (keys) because that will lead to confusion whether the term is an abbreviation or a URL.

Here's what the spec says https://w3c.github.io/json-ld-syntax/#terms :

to avoid confusion between a Compact IRI and a term, terms SHOULD NOT include a colon (:) and SHOULD be restricted to the form of isegment-nz-nc as defined in [RFC3987].

https://www.rfc-editor.org/rfc/rfc3987#section-2.2:

isegment-nz-nc = 1*( iunreserved / pct-encoded / sub-delims / "@" )
   ; non-zero-length segment without any colon ":"
iunreserved = ALPHA / DIGIT / "-" / "." / "_" / "~" / ucschar
ucschar = %xA0-D7FF / %xF900-FDCF / %xFDF0-FFEF / %x10000-1FFFD / %x20000-2FFFD / %x30000-3FFFD / %x40000-4FFFD /
  %x50000-5FFFD / %x60000-6FFFD / %x70000-7FFFD / %x80000-8FFFD / %x90000-9FFFD / %xA0000-AFFFD /
  %xB0000-BFFFD / %xC0000-CFFFD / %xD0000-DFFFD / %xE1000-EFFFD
sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

As you see, forward slash is forbidden.

Let me illustrate the problem:

{
  "@context": {
    "@version": 1.1,
    "@vocab": "https://example.org/",
    "a/b": "https://a"
  },
  "@id": "https://id",
  "a/b": 2 # is this https://a or https://example.org/a/b ?
}

What other punctuation is allowed in JSON-LD keys? You'd have to check all ranges of ucschar.
I'm too lazy to do that, but the same RFC says

Systems accepting IRIs MAY also deal with the printable characters in US-ASCII that are not allowed in URIs, namely "<", ">", '"', space, "{", "}", "|", "", "^", and "`"

Because these punctuations are forbidden in URIs, I think that they are allowed in JSON-LD keys.

[jakubklimek]

@VladimirAlexiev fair point about the RFC3987 reference in the JSON-LD spec, I have missed that.

In your example, I would understand the problem with "a:b", I do not understand it with "a/b" though, how could it be https://example.org/a/b? Only values with colons : are interpreted as compact IRIs, not with slashes.

[VladimirAlexiev]

@jakubklimek
Is a/b a relative URL (to be expanded with @vocab) or an abbreviated term (as you defined it)?

[jakubklimek]

@VladimirAlexiev ahh, right. I forgot about @vocab and that in that case, JSON keys also directly represent parts of URIs.

Therefore, this is actually not an issue and can be closed.