Understand xml files

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But in general URIs are not required to be resolvable in themselves , so you can't count on someone else's URI being directly resolvable to a physical file. Which is why XML documents may include schemaLocation attributes - to indicate the physical location of the files needed to define name spaces or to be imported into the current document. The catalog file maps the values of public identifiers , system identifiers and URIs generally to other URIs that actually do resolve to a physical file.

It will do this for anything your application considers to be an external id either a public identifier or a system identifier , as well as for any other URIs it encounters. These can be copied verbatim from any valid catalog file; if you use an XML Catalog generation tool, these will be provided for you.

As explained above, for PDS purposes this preference setting is meaningless - we'll only be mapping URIs, not external identifiers. If you think you might need or want them, read the standard carefully and have at it.

Following are some simple XML Catalog files for a couple of common scenarios. Note that these all contain both the DOCTYPE reference and the catalog namespace reference " urn:oasis:names:tc:entity:xmlns:xml:catalog ".

The uri statements have to come first because the catalog processor will stop with the first statement that matches - so in this case if the rewriteURI statement came first, the processor would never make it past there.

Alternately, if you're working with several mission dictionaries in active development scattered across your disc space or network, you might want to use a catalog file specifically to handle the mission dictionaries and use your local schema tree for the rest.

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