Hi everyone.
I'm making good progress on the Distro-Constructor manifest. I have
written a mostly-complete first-cut RelaxNG schema and a test manifest.
I can validate the test manifest using xmllint. Schema and test
manifest are attached.
I can parse the XML data into an in-memory DOM structure. Next is to
provide an easy-to-use set of interfaces (based on DOM interfaces) to
read/change/add in-memory data.
RelaxNG does have its limitations. While it's great for validating the
format/syntax of XML documents (e.g. that all required attributes are
present for a given item) and is easiest to read of the schema types I
investigated, it does not do an adequate job of content/semantic
validation. (An example of content validation is that an IP address
isn't set to "junk".) RelaxNG, being a schema, does not set defaults
either, since schemas come into play only during validation.
I propose a second manifest to specify defaults and node-specific
content checking. This second manifest would be shipped with the
product, and is not intended for modification by end users. An engine
would read this manifest, and massage/check the in-memory data based on
it. This approach offers validation and setup of defaults which is as
easy and maintainable as the schema. The second manifest will require
an update only when the schema changes, and both can be easily kept in sync.
Note that the in-memory data update mechanism to be used can also be
used for layering. Additional (sparse) manifests can be read for
additional data, and changes layered on top of existing in-memory data.
When layering is complete, the final data set can be checked against the
schema. It can also be saved as an XML doc for future reference or as a
starting point for future changes.
Comments and suggestions are welcomed.
Thanks,
Jack
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