- From: <noah_mendelsohn@us.ibm.com>
- Date: Mon, 9 Jan 2006 18:13:10 -0500
- To: Jon Hanna <jon@hackcraft.net>
- Cc: www-tag@w3.org
Jon Hanna writes: > As either a document recipient, creator, publisher or anything > else I want the document to be valid against a shared schema > deemed useful by all parties (whether explicitly, or through > the schema being "well-known"). In framing things this way, I think you've ruled out many of the most interesting use cases that the Schema WG has been considering regarding versioning [1]. XML is in part useful for communication between loosely coupled organizations, and experience suggests that author and consumer may evolve their software at different times. The trick with versioning is not to have a "shared schema deemed useful", but an ability to detect the degree to which interoperation is safe between two parties who may have somewhat differing views of the schemas. Maybe or maybe not schemaLocation is a helpful or appropriate hook, but I strongly object to the suggestion that in the general case there is one schema to which both parties must agree. On the contrary, they must reliably discover in the face of potentially conflicting schemas which parts, if any, of the communication can be reliably interpreted, in the sense that a) the receiver correctly determines what the sender has intended to transmit and b) that the receiver does not inadvertently miss something essential (I.e. everything you act on is correct, and you don't fail to notice something that makes proceeding unsafe.) Even if the latest schema is available directly or indirectly from the namespace URI, that doesn't guarantee interoperation of such software written at different times. There is likely to be a lot of logic in a program that doesn't update automatically when a new schema is received. At best such a program might retrieve the schema and discover: oops, looks like someone's changed the schema since my code was written. Even then, I'll be curious whether the person who wrote this message knew about the latest changes. Noah [1] http://www.w3.org/2005/05/xsd-versioning-resources.html [2] http://www.w3.org/XML/2005/xsd-versioning-use-cases/ -------------------------------------- Noah Mendelsohn IBM Corporation One Rogers Street Cambridge, MA 02142 1-617-693-4036 --------------------------------------
Received on Monday, 9 January 2006 23:13:16 UTC