Versioning and subreferences in URNs

Optional methods

The example URN type for ISBN numbers developed in the tutorials doesn’t require versioning (ISBN-10 values are fixed values) or support for subreferences (the ISBN-10 value is complete and can’t be further reference). of those features, but we’ll use that type to show how they can be implemented.

We’ll use the simple ISBN URN type to show how support for those features can be implemented: see the CtsUrn (from CitableText) or the Cite2Urn (from CitableObject) for examples of URN types supporting those optional behaviors.

We start from a type that is a subtype of the abstract Urn.

using CitableBase
struct Isbn10Urn <: Urn
    isbn::AbstractString
end

canwebewrong = Isbn10Urn("urn:isbn10:1108922036")

Isbn10Urn("urn:isbn10:1108922036")

Versioning

URN types that support versioning must implement three functions: supportsversion, addversion and dropversion.

We’ll indicate that our URN type supports versioning but for this demonstration will just pass the URN through unchanged.

import CitableBase: supportsversion
function supportsversion(u::Isbn10Urn)
    true
end

import CitableBase: addversion
function addversion(u::Isbn10Urn, versioninfo::AbstractString)
    u
end

import CitableBase: dropversion
function dropversion(u::Isbn10Urn)
    u
end

dropversion (generic function with 2 methods)

supportsversion(canwebewrong)

true

addversion(canwebewrong, "v2")

Isbn10Urn("urn:isbn10:1108922036")

dropversion(canwebewrong)

Isbn10Urn("urn:isbn10:1108922036")

Subreferences

URN types that support subreferences on identifiers must implement four functions: supportssubref, dropsubref, addsubref and hassubref.

import CitableBase: supportssubref
function supportssubref(u::Isbn10Urn)
    true
end

import CitableBase: dropsubref
function dropsubref(u::Isbn10Urn)
    u
end

import CitableBase: hassubref
function hassubref(u::Isbn10Urn)
    false
end

import CitableBase: subref
function subref(u::Isbn10Urn)
    nothing
end

subref (generic function with 3 methods)

supportssubref(canwebewrong)

true

hassubref(canwebewrong)

false

dropsubref(canwebewrong)

Isbn10Urn("urn:isbn10:1108922036")

subref(canwebewrong)