api - RESTful - Different URI of same resource to get different forms of same resource -

i'm pushed peculiar situation i'm not able decide wrong , right.

i've resource called invoice. json or xml representation use below uri

somedomain.com/inovices/{invoicenumber} - invoice number numeric accept: application/xml 

when want pdf of same resource use below uri:

somedomain.com/inovices/{invoicenumber} - invoice number numeric accept: application/pdf 

both above url's served authenticated requests. want support same resource using guid unauthenticated requests, hence want use below url

somedomain.com/inovices/{guid} accept: application/pdf 

above url permanent url , can access url number of times. confusion whether providing url above restful or not. because in 1 url i'm using invoice number numeric , permanent url i'm replacing guid.

reason why felt wrong same resource represented 2 different uri's (number , guid) though returning same resource. or assumption wrong? against rest cosntraint i'm not able understand?

there's no problem @ different uris point @ same resource. it's not ok, it's recommended, if add value user.

think of these examples:

get /api/users/543 /api/users/bob-marley 

or, does:

get /questions/16637720/restful-different-uri-of-same-resource-to-get-different-forms-of-same-resource /q/16637720/1118323 

there similar examples everywhere. may want add "unnessecary" information if it's going users, or seo, , still keep short version available. or imagine senarios, want add more ways of accessing resources without breaking existing ones. sounds quite common me , don't break rules having more 1 uri same resource.

if worried user might think 2 resources different since used different uri, can have 1 uri redirect other, make explicit it's same resource (as when hit short link, or link without thread heading).

here relevant answer.