RDF/POST is a syntax for encoding an RDF graph as HTTP GET URL query string or POST form-urlencoded request body. It can be used for building RDF editing interfaces with plain HTML forms (no JavaScript required).

This document is based on the original RDF/POST draft by Sergei Egorov.

RDF/POST Grammar

This EBNF is defined in XML 1.0 second edition [[XML]].

Parsing

The use of this format in HTML pages relies on the fields are listed in the order they appear requirement of the HTML Forms specification. Since HTML user agents are not required to send fields with null values (browsers are free to ignore them), such fields should not be used to send pairs which are important for correct decoding of the format (e.g. a pair defining the subject of a triple). Remember that hidden fields are always sent if they have value attributes present.

To handle data submitted from HTML forms, the decoder should allow for some missing pairs, skipping to the next sync point (if any) and silently ignoring the affected triples:

• pred is expected, but there is no &pv=, &pn=, or &pu= ahead: skip to the next subj (&sb=, &su=, &sv=, &sn=).
• &pn= name is seen, but there's no &pv= ahead: skip to the next subj (&sb=, &su=, &sv=, &sn=).
• obj is expected, but there is no &ob=, &ov=, &on=, &ou=, or &ol= ahead: skip to the next pred (&pu=, &pv=, or &pn=) or subj (&sb=, &su=, &sv=, &sn=), whichever comes first.
• &on= name is seen, but there's no &ov= ahead: skip to the next pred (&pu=, &pv=, or &pn=) or subj (&sb=, &su=, &sv=, &sn=), whichever comes first.
• &lt= or &ll= is seen, but there is no &ol= ahead: skip to the next non-literal obj (&ob=, &ou=, &ov=, or &on=), pred (&pu=, &pv=, or &pn=) or subj (&sb=, &su=, &sv=, &sn=), whichever comes first.

Strings can contain any Unicode character encoded in UTF-8 and, if the resulting octets fall outside of US_ASCII, urlencoded as described in Form content types - application/x-www-form-urlencoded [[HTML401]]. The simplest way to ensure that browsers send form data in UTF-8 is to encode form pages in UTF-8.

Examples

Here is a simple RDF/POST document encoded in a simple HTML form:

The HTML code of this form looks like this:

<form>
    <p>
        <input type="hidden" name="rdf" value=""/>

        <!-- namespace declarations -->
        <input type="hidden" name="v" value="http://xmlns.com/foaf/0.1/"/>
        <input type="hidden" name="n" value="rdf"/>
        <input type="hidden" name="v" value="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
        <input type="hidden" name="n" value="dc"/>
        <input type="hidden" name="v" value="http://purl.org/dc/elements/1.1/"/>

        <!-- triples -->
        <span>Someone called</span>
        <input type="hidden" name="sb" value="o"/>
        <input type="hidden" name="pv" value="givenName"/>
        <input type="text" name="ol" value="Ora" size="10"/>

        <input type="hidden" name="pv" value="familyName"/>
        <input type="text" name="ol" value="Lasilla" size="10"/>

        <input type="hidden" name="pn" value="dc"/>
        <input type="hidden" name="pv" value="creator"/>
        <input type="hidden" name="ob" value="b"/>

        <input type="hidden" name="sb" value="b"/>
        <input type="hidden" name="pn" value="rdf"/>
        <input type="hidden" name="pv" value="type"/>
        <select name="ov">
            <option selected="selected" value="Document">wrote a book</option>
            <option value="Image">painted a picture</option>
        </select>

        <span>titled</span>
        <input type="hidden" name="pn" value="dc"/>
        <input type="hidden" name="pv" value="title"/>
        <input type="text" name="ol" value="Moby Dick" size="20"/>

        <button type="submit">Post</button>
    </p>
</form>

During form submission, the browser constructs the following query string (spaces and indentation are added for presentation purposes):

rdf=
&v=http://xmlns.com/foaf/0.1/
&n=rdf &v=http://www.w3.org/1999/02/22-rdf-syntax-ns%23
&n=dc &v=http://purl.org/dc/elements/1.1/
&sb=o
 &pv=givenName
  &ol=Ora
 &pv=familyName
  &ol=Lasilla
 &pn=dc &pv=creator
  &ob=b
&sb=b
 &pn=rdf &pv=type
  &ov=Document
 &pn=dc &pv=title
  &ol=Moby+Dick

It can be compared line-by-line with the equivalent Turtle description:

@prefix : <http://xmlns.com/foaf/0.1/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns%23> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
_:o
 :givenName
  "Ora" ;
 :familyName
  "Lasilla" ;
 dc:creator
  _:b .
_:b
 rdf:type
  :Document ;
 dc:title
  "Moby Dick" .

If one wants to make sure that submitted data conforms to RDF datatype requirements, e.g. does not contain unexpected empty string values and incorrectly formatted dates, the forms can be validated with Javascript code.