RE: Data streams and schema use and identification
Dan Vint write: >I'm not looking to make something up, I'm trying to find a standard way of >doing this. I could have lived with the idea that if you use W3C schemas >you need the xsi attributes, etc in the data stream. I wasn't given that >and all I'm left with is the possibility of something that looks just like >a well-formed XML stream - with no idea what to validate it with. In XForms  we explicitly state that xsi:schemaLocation and friends are ignored inside the instance document, and provide an attribute on the <model> element to allow the author to specify a normative list of Schema URI references that must be resolved to provide the Schema components for assessment. XForms further allows direct inclusion of the <xs:schema> element inside the model. <xs:schema> elements may appear outside the <model> but in the enclosing document and be referred to fromn the model@schema attribute as fragments, if the host language supports fragments. So, in the sense of the original question, for XForms there is an XML document that states what Schema defines the document validity, but the two are not the same document: we require the enclosing document to define validity for the included or referenced "instance document." The enclosing document is the XForms document, which itself is further embedded in a host document such as an XHTML or SVG document. We can do this because processors can be directed to ignore xsi:schemaLocation at the request of the system invoking the processor, and must do this because the instance data and the form itself come from different places, and likely have different authors and different levels of trust. Use case details: The back-end server that accepts the POST is the ultimate arbiter of document validlty. The form author is responsible for the user's interaction with the back-end server, and must be able to instruct the user agent to act in the combined best interests of the user and the server. (I.e., it's no good for anybody to allow the user to submit a purchase order with a bogus discount element in it.) The situation is similar for the initial instance data, which may come from a separate source than the form that edits it. One point that novice users of XForms and XML Schema often miss is that there are multiple Schema files, one per namespace, so the model@schema attribute is a space-separated list. One point that novice users of XForms and XML Schema often miss is that there are multiple Schema files, one per namespace, so the model@schema attribute is a space-separated list. XForms does not follow the xsi:schemaLocation pattern of alternating namespace and URI references, because we require the XForms processor to resolve all of the URI references, and thus the xs:schema@targetNamespace attribute provides the namespace.  http://www.w3.org/TR/xforms
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