Provide shape for Data Model section

[elf-pavlik]

The current description somehow makes sense for JSON-LD, but it isn't very clear as content type independent definition.
Providing a shape in ShEx and SHACL should provide an unambiguous and validatable way of defining it.

I can write one in ShEx, it can also constrain that it has to use IRI and can't be a blank node, it would go something like this:

:Notification IRI {
  a [ as:Update as:Add as:Delete as:Create ] ;
  as:object IRI;
  as:published xsd:dateTime ;
  notify:state xsd:string
}

[CxRes]

This is a good idea.

We will need an as:object line as well.

Finally, I am not sure if conditionals can be expressed in SHACL or ShEx?

[CxRes]

ACTION: @elf-pavlik will make a PR with ShEx template.