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Re: Proposed new specification for THREDDSS Catalogs



Roland Schweitzer wrote:

John,

I have a question about the THREDDS Dataset Inventory Catalog XML. I don't intend this as a criticism, but rather I'm curious about the choices and trade-offs. All of us that are messing around with XML are wrestling with similar issues.

In general, it seems that relationships between elements in the XML are done via attributes. For example, a <service> element is referred to in the document via the serviceName attribute in the <dataset> element. And a <dataset> element can be repeated by referencing the name of another <dataset> element via the alias attribute.

It seems to me that using this technique then requires that client code must be written to follow these connections. By contrast, it seems that the XML community has attempted to create languages (like XPointer) that would "standardize" these sorts of references. Admittedly, even though the XPointer recommendation is a year old, I have not found (m)any implementations in general purpose XML software.

Can you please comment on these choices and trade-offs for defining the internal connections between bit of XML that went into developing the Inventory Catalog?

Thanks,
Roland

Hi Roland:

<excuse> Sorry its taken me so long to answer this </excuse>

Anyway, its not clear that the XPointer spec will become an official standard. XPath seems useable though, and i am open to it. Both the serviceName and the alias = dataset ID are more or less the simple case of XPath using IDs. I think using IDs for datasets is so useful that it should probably be required. Which I would do if we could do so and still allow the minimal datasets like the DODS File Server. This ID reference is so simple that even DTDs have it.

So Id say full XPath is a bit of overkill right now, but i am open to using it in the future. Do you forsee any new features that might need it?



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