When referencing an entity from another page, should only @id and @type be specified, or should all necessary attributes be duplicated?

Question

I have multiple web pages in my website; "about" page (e.g.: http://example.com/about/) and "blog" pages (e.g.: http//:example.com/blog/1/).

In the "about" page, I have defined authors of the website. Each author has given a proper @id attribute.

Articles of the blog pages are written by someone from that author list in the "about" page. When I'm specifying the author of an article in a "blog" page, what should I do?

"author": {
    "@type": "Person",
    "@id": "http://example.com/about/#user1"
}

1. Specify the author with only the above information (is @type really needed here?)
2. Specify all the necessary attributes of the author (duplicate the item from "about" page)

Answer 1

Theoretically, it’s sufficient to specify only the @id:

"author": {"@id": "http://example.com/about/#bob"}

If a consumer already knows the entity with this @id URI (e.g., after having crawled the "about" page), they don’t need to see its properties here again.
If a consumer doesn’t already know the entity with this URI, they have the chance to learn more about it by visiting the URL and looking for an entity with the @id URI.

In practice, however, consumers don’t necessarily 1) remember which entities they found, and/or 2) visit referenced URLs. For example, if the consumer is a search engine, they might only care about what’s on the current page (e.g., because they want to display a rich result for it), ignoring every reference to other pages for this context.

So, it can be good idea to provide more data about a referenced entity.

If you know that a consumer expects certain properties on the current page, you should of course provide (at least) these. For example, Google’s Article rich result for AMP pages requires the type and name of an author.

If you don’t know what possible consumers expect, I think it makes sense to always provide at least the URI (@id) and type (@type) as well as the Schema.org properties name and url.

"author": {
  "@type": "Person",
  "@id": "http://example.com/about/#bob",
  "url": "http://example.com/about/#author-bob",
  "name": "Bob"
}

(@id and url have different values, because @id represents the actual person, while url represents the page (or page section) about this person.)