I need to create a RESTful webservice that allows for addressing entities by using different types of IDs. I will give you an example based on books (which is not what I need to process but I want to build a common understanding this way).

Books can be identifier by:

* ISBN 13
* ID
* title

I can create a book by `POST`ing to `/api/v1/books/The%20Bible`. This book can then later be addressed by its ISBN `/api/v1/books/12312312301` or ID `/api/v1/books/A9471IZ1`. If I implemented it this way I would need to analyze whatever identifier gets sent and convert it internally. 

Is it 'legal' to add the type of identifier to the URL ? Like `/api/v1/books/title/The%20Bible`?