plural properties should become singular

Dear all,

TL;DR: Since the range of the following properties is not a list, I think they should be singular:
- hydra:mappings
- hydra:members
- hydra:operations
- hydra:statusCodes
- hydra:supportedClasses
- hydra:supportedOperations
- hydra:supportedProperties
This mail argues why plural properties are not a good idea.

In the RDF data model, a property creates a relation between a subject and an object.
For instance, :subject :hasP :object means that “subject has object as P".
We see examples of that in all popular vocabularies. Examples:
RDF – :me rdf:type foaf:Person, foaf:Agent.
FOAF – :me foaf:interest, :Web, :Hypermedia.
Dublin Core – ;document dc:hasPart :part1, :part2.

As you can see, it doesn't matter whether one or multiple properties are expected:
multiple objects can be attached to the same subject; but all are different relations.
The property is singular because it describes a relation between two (singular) things.
The only time we would encounter a plural, is if the object is a list/collection.

If we look at Hydra, this is not defined as one would expect:
    {
      "@id": "hydra:mappings",
      "@type": "rdf:Property",
      "comment": "The variable-to-property mappings of the IRI template.",
      "domain": "hydra:IriTemplate",
      "label": "mappings",
      "range": "hydra:IriTemplateMapping",
      "status": "testing"
    },

This can lead to situations such as
    :Template hydra:template "/issues{?q}" ;
        hydra:mappings :q.
    :q a hydra:IriTemplateMapping;
        hydra:property hydra:freetextQuery;
        hydra:required true;
        hydra:variable "q" .

So the “mappings” of /issues{?q} is actually a single mapping.
Or in other words: /issues{?q} has "mappings” :q,
but :q is only a single mapping, not a collection of mappings.
Let me trim down the example to show this contradiction better:
    :Template hydra:mappings :q.
    :q a hydra:IriTemplateMapping.
Either :q should be hydra:IriTemplateMappings,
or the property should be singular: "hydra:mapping".

The case of “statusCodes” shows to how much confusion this leads:
we have both a “statusCode” and a ”statusCodes” property.
The situation would be that a resource can lead to “statusCodes" X, Y, Z,
each of which have a “statusCode” 200, 400, 500, respectively.
I think the correct way is that “statusCodes” becomes “status”,
and that the current statusCode remains the way it is.

I would strongly suggest that all of the aforementioned properties are turned into singular;
that would align Hydra with the best practices of all other vocabularies.
I know that changing this can be a pain, but I think it's important we do this.

Best,
-- 
Ruben Verborgh
PhD Researcher in Semantic Hypermedia
iMinds – Multimedia Lab – Ghent University, Belgium
http://ruben.verborgh.org/ – @RubenVerborgh

Received on Tuesday, 28 January 2014 17:32:12 UTC