How to manage multiple JSON schema files?

In JSON Schemas, you can either put a schema per file and then access them using their URL (where you stored them), or a big schema with id tags.

Here is for one big file:

{
    "id": "#root",
    "properties": {
        "author": {
            "id": "#author",
            "properties": {
                "first_name": {
                    "type": "string"
                },
                "last_name": {
                    "type": "string"
                }
            },
            "type": "object"
        },
        // author
        "author_api": {
            "id": "#author_api",
            "items": {
                "$ref": "author"
            },
            "type": "array"
        },
        // authors API
        "book": {
            "id": "#book",
            "properties": {
                "author": {
                    "type": "string"
                },
                "title": {
                    "type": "string"
                }
            },
            "type": "object"
        },
        // books API: list of books written by same author
        "books_api": {
            "id": "#books_api",
            "properties": {
                "author": {
                    "$ref": "author"
                },
                "books": {
                    "items": {
                        "$ref": "book"
                    },
                    "type": "array"
                }
            },
            "type": "object"
        }
    }
}

You can then reference your validator to one of those sub schemas (which are defined with an id).

From outside of your schema, this:

{ "$ref": "url://to/your/schema#root/properties/book" }

is equivalent to this:

{ "$ref": "url://to/your/schema#book" }

… which is equivalent, from inside, to this:

{ "$ref": "#root/properties/book" }

or this (still from inside):

{ "$ref": "#book" }

See my answer here for more information.