Describe lists containing lists, as motivated by GeoJSON. #41
There are no files selected for viewing
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
|
@@ -26,13 +26,13 @@ | |
| prevVersion: "https://www.w3.org/TR/2014/REC-json-ld-20140116/", | ||
| previousPublishDate: "2014-01-16", | ||
| previousMaturity: "REC", | ||
| github: "https://github.com/w3c/json-ld-syntax/", | ||
|
|
||
| // if there a publicly available Editor's Draft, this is the link | ||
| edDraftURI: "https://w3c.github.io/json-ld/", | ||
|
|
||
| includePermalinks: true, | ||
| doJsonLd: true, | ||
| postProcess: [internalizeTermListReferences], | ||
|
|
||
| // if you want to have extra CSS, append them to this list | ||
|
|
@@ -95,8 +95,6 @@ | |
| note: "v1.0" } | ||
| ], | ||
|
|
||
| // name of the WG | ||
| wg: "JSON-LD Working Group", | ||
|
|
||
|
|
@@ -2301,9 +2299,188 @@ <h2>Sets and Lists</h2> | |
| --> | ||
| </pre> | ||
|
|
||
| <p>The implementation of <a>lists</a> in RDF depends on linking anonymous nodes | ||
| together using the properties <code>rdf:first</code> and | ||
| <code>rdf:rest</code>, with the end of the list defined as the resource | ||
| <code>rdf:nil</code>. This can be represented as triples, as the following | ||
| example shows:</p> | ||
|
|
||
| <table class="example"> | ||
| <thead><tr> | ||
| <th>Subject</th> | ||
| <th>Property</th> | ||
| <th>Value</th> | ||
| </tr></thead> | ||
| <tbody> | ||
| <tr> | ||
| <td>http://example.org/people#joebob</td> | ||
| <td>foaf:nick</td> | ||
| <td>_:b0</td> | ||
| </tr> | ||
| <tr> | ||
| <td>_:b0</td> | ||
| <td>rdf:first</td> | ||
| <td>joe</td> | ||
| </tr> | ||
| <tr> | ||
| <td>_:b0</td> | ||
| <td>rdf:rest</td> | ||
| <td>_:b1</td> | ||
| </tr> | ||
| <tr> | ||
| <td>_:b1</td> | ||
| <td>rdf:first</td> | ||
| <td>bob</td> | ||
| </tr> | ||
| <tr> | ||
| <td>_:b1</td> | ||
| <td>rdf:rest</td> | ||
| <td>_:b2</td> | ||
| </tr> | ||
| <tr> | ||
| <td>_:b2</td> | ||
| <td>rdf:first</td> | ||
| <td>jaybee</td> | ||
| </tr> | ||
| <tr> | ||
| <td>_:b2</td> | ||
| <td>rdf:rest</td> | ||
| <td>rdf:nil</td> | ||
| </tr> | ||
| </tbody> | ||
| </table> | ||
|
|
||
| <p>JSON-LD provides a syntactic shortcut for these lists. In Turtle, the graph would be expressed as follows:</p> | ||
|
|
||
| <pre class="example" data-transform="updateExample" | ||
| data-content-type="text/turtle" | ||
| title="An ordered collection of values in Turtle"> | ||
| <!-- | ||
| @prefix foaf: <http://xmlns.com/foaf/0.1/> . | ||
|
|
||
| <http://example.org/people#joebob> foaf:nick ("joe" "bob" "jaybe") . | ||
| --> | ||
| </pre> | ||
|
|
||
| <p class="changed">In JSON-LD 1.1, lists of lists, where the value of | ||
| a <a>list object</a>, may itself be a <a>list object</a>, are | ||
| fully supported. For example, in <em>GeoJSON</em> (see [[RFC7946]]), | ||
| <em>coordinates</em> are an ordered list of <em>positions</em>, which are | ||
| represented as an array of two or more numbers:</p> | ||
|
|
||
| <pre class="example changed" | ||
| data-content-type="application/json" | ||
| title="Coordinates expressed in GeoJSON"> | ||
| { | ||
| "type": "Feature", | ||
| "bbox": [-10.0, -10.0, 10.0, 10.0], | ||
| "geometry": { | ||
| "type": "Polygon", | ||
| "coordinates": [ | ||
| [ | ||
| [-10.0, -10.0], | ||
| [10.0, -10.0], | ||
| [10.0, 10.0], | ||
| [-10.0, -10.0] | ||
| ] | ||
| ] | ||
| } | ||
| //... | ||
| } | ||
| </pre> | ||
|
|
||
| <p class="changed">For these examples, it's important that values | ||
| expressed within <em>bbox</em> and <em>coordinates</em> maintain their order, | ||
| which requires the use of embedded list structures. In JSON-LD 1.1, we can | ||
| express this using recursive lists, by simply adding the appropriate context | ||
| definion:</p> | ||
|
|
||
| <pre class="example changed" | ||
| data-content-type="application/json" | ||
| data-transform="updateExample" | ||
| title="Coordinates expressed in JSON-LD"> | ||
| { | ||
| "@context": { | ||
| "@vocab": "https://purl.org/geojson/vocab#", | ||
| "type": "@type", | ||
| "bbox": {"@container": "@list"}, | ||
| "coordinates": {"@container": "@list"} | ||
|
There was a problem hiding this comment. In geojson/geojson-ld#34 we discussed an |
||
| }, | ||
| "type": "Feature", | ||
| "bbox": [-10.0, -10.0, 10.0, 10.0], | ||
| "geometry": { | ||
| "type": "Polygon", | ||
| "coordinates": [ | ||
| [ | ||
| [-10.0, -10.0], | ||
| [10.0, -10.0], | ||
| [10.0, 10.0], | ||
| [-10.0, -10.0] | ||
| ] | ||
| ] | ||
| } | ||
| ####//...#### | ||
| } | ||
| </pre> | ||
|
|
||
| <p>This is equivalent to the expanded form, which uses <a>list objects</a>:</p> | ||
|
|
||
| <pre class="example changed" | ||
| data-content-type="application/json" | ||
| data-transform="updateExample" | ||
| title="Coordinates expressed in JSON-LD (expanded)"> | ||
| [{ | ||
| "@type": ["https://purl.org/geojson/vocab#Feature"], | ||
| "https://purl.org/geojson/vocab#bbox": [{ | ||
| "@list": [ | ||
| {"@value": -10.0}, | ||
| {"@value": -10.0}, | ||
| {"@value": 10.0}, | ||
| {"@value": 10.0} | ||
| ] | ||
| }], | ||
| "https://purl.org/geojson/vocab#geometry": [{ | ||
| "@type": ["https://purl.org/geojson/vocab#Polygon"], | ||
| "https://purl.org/geojson/vocab#coordinates": [{ | ||
| "@list": [{ | ||
| "@list": [ | ||
| {"@list": [{"@value": -10.0}, {"@value": -10.0}]}, | ||
| {"@list": [{"@value": 10.0}, {"@value": -10.0}]}, | ||
| {"@list": [{"@value": 10.0}, {"@value": 10.0}]}, | ||
| {"@list": [{"@value": -10.0}, {"@value": -10.0}]} | ||
|
There was a problem hiding this comment. This is fine. Tagential question: is there a way to indicate to JSON-LD users that the first element of these 2-tuples is longitude and the second is latitude? There was a problem hiding this comment. Not really. If the vocabulary were modeled in OWL, there may be some way to do this at that level, @iherman may know better. There was a problem hiding this comment. To be honest, even in OWL I don't see a way to do that. There was a problem hiding this comment. From a graph modeling perspective, the fact that the lat/long were originally presented in a list isn't important, is it? Only the "outer" list of coordinates has value to the graph (afaict). |
||
| ] | ||
| }] | ||
| }] | ||
| }] | ||
| }] | ||
| </pre> | ||
|
|
||
| <p class="changed">Note that <em>coordinates</em> includes three levels of lists. | ||
| When expressed in Turtle, this would be the following:</p> | ||
|
|
||
| <pre class="example changed" | ||
| data-content-type="text/turtle" | ||
| title="Coordinates expressed in Turtle"> | ||
| <!-- | ||
| @prefix geojson: <https://purl.org/geojson/vocab#>. | ||
|
|
||
| [ | ||
| a geojson:Feature ; | ||
| geojson:bbox (-10.0 -10.0 10.0 10.0) ; | ||
| geojson:geometry [ | ||
| a geojson:Polygon ; | ||
| geojson:coordinates ( | ||
| ( | ||
| (-10.0 -10.0) | ||
| (10.0 -10.0) | ||
| (10.0 10.0) | ||
| (-10.0 -10.0) | ||
| ) | ||
| ) | ||
| ] | ||
| ] . | ||
| --> | ||
| </pre> | ||
|
|
||
| <p>While <code>@list</code> is used to describe <em>ordered lists</em>, | ||
| the <code>@set</code> keyword is used to describe <em>unordered sets</em>. | ||
|
|
@@ -5118,6 +5295,7 @@ <h2>Changes since 1.0 Recommendation of 16 January 2014</h2> | |
| a context. When this is set, vocabulary-relative IRIs, such as the | ||
| keys of <a>node objects</a>, are expanded or compacted relative | ||
| to the <a>base IRI</a> using string concatenation.</li> | ||
| <li><a>Lists</a> may now have members which are themselves <a>lists</a>.</li> | ||
| </ul> | ||
| </section> | ||
|
|
||
|
|
||
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
I feel that GeoJSON examples can be made less confusing with respect to longitude, latitude ordering by using real-world coordinates like
[-105.615115, 40.255014](latitude: 40.255 degrees N, longitude: 105.615 degrees W).There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Note that the lists of lists feature does not preclude #34, although it becomes less important, and it does add significantly more complexity to the processing model.