[Application-profiles-ig] schema profile for google recipes

Wed May 27 11:21:18 BST 2020

On 2020-05-26 08:17, Karen Coyle wrote: >[3] This brings up another question that I will add the list of running>questions, which is: by default, is an AP open (in the RDF sense) or closed?>While ShEx has a default of open, I think that the main purpose of an AP is>可预见性,therefore "closed" seems to be the right answer.In the DC context, historically, application profiles started off largely as expressions of rough consensus within a community -- guidelines in the form of specifications published as Web pages rather than as validation schemas, as things that could easily be extended with extra properties rather than as rules saying "use these properties with these constraints and no others". In a ShEx schema (a collection of shape expressions), any particular shape can be marked as closed, which means: "Data conforms to the shape if it consists _entirely_ of triples using _these_ properties with _these_ constraints". By default, using a property in a ShEx shape "closes" that property in the context of the shape, so the property-value pair "rdf:type foaf:Person" closes "rdf:type" by saying it must be used only with the value foaf:Person -- unless the keyword "EXTRA" is added, in which case a person could be described with additional (and unspecified) outgoing rdf:type arcs such as "rdf:type ex:Human". The ShEx defaults seem like a reasonable starting point: shapes open w.r.t properties, individual properties within a shape closed w.r.t value constraints. We could decide to articulate different default assumptions about openness for the purposes of the template. We might even be able to find a way to squeeze CLOSED and EXTRA into the template if we really wanted. However, I do not think it would be productive to try to engineer more subtle expressivity for what should be a very simple tabular format. I'd rather see us focus on completing a simple template, with examples, with well-articulated assumptions, and encourage users who need more to use the template as an on-ramp for schemas in more expressive languages such as ShEx. It is hard enough to explain these subtleties to ShEx users and would be no easier to explain to users of the template. -- Tom Baker <tom at tombaker.org>