XML Wishes (</>, quotes and entity resolution)
jarle.stabell at dokpro.uio.no
Wed Oct 1 22:23:46 BST 1997
Jarle Stabell wrote:
> 1. Please incorporate the </> tag, it would take a parser-writer 5 minutes to implement it, as well as save
bandwitdth, diskspace, typing and in some cases ease reading. (It could also be used to write
hard-to-understand/maintain documents, but that's up to the user)
Murray Altheim writes:
As both a document type designer, a parser writer, and a document author,
I think one of the main advantages to XML is the requirement of explicitly-
named end tags.
[MA] The save-typing argument is moot in that most people will
probably not hand-edit tags.
[JS] Maybe. But I know I will. Therefore I would like it. :-)
I really think
are faster/easier to read than
and I keep seeing lots of things like this.
Having this possibility would perhaps also prevent people from using "cryptic" abbreviations as element type names/ID's
I agree that closing an element having subelements with a </> would be a "bad thing" for a document writer to do.
[MA] For those that do, having the explicit end
tags is probably a Very Good Thing, in that it saves confusion. And while it
maybe only takes '5 minutes' (NOTHING takes five minutes) to add in a parser,
suddenly a simple parser must build a document tree in order to know which
element is being closed by '</>', which makes simple parsers into much more
complicated ones. This is not a benefit.
[JS] Ok, I didn't think of the possibility of anyone building XML parsers without building the document tree. (I won't disclose any estimate for building the document tree...:-) )
> [JS] 2. Allow non-quoted attribute values. I guess support for this is also a 5 minutes project for the
[MA] We're up to ten minutes. Actually, this makes the parser more complicated,
since knowing that attribute values are delimited allows a simple 'scan-literal'
approach, ie., if the first character after the equals sign is a single quote,
one scans to the next single quote. If a double, scan to the next double. If
they are optional things get much more complicated, and we now must care about
what type of characters are in the content of the literal. Options and
minimization features generally add a lot of work for parser writers.
[JS] I think the complexity this adds for the parser writers are neglible, it's a very local thing, typically located to a single method/routine.
If having the possibility of omitting the quotes would benefit users, perhaps by making it more SGML compatible, I definitely think one should allow this. I've already seen documents on the web stated as being XML documents without the quotes. If some parsers allow it (I don't know!), then the other parsers would seem unecessary "stubborn" from a user's perspective.
> [JS] 3. Add a paragraph to the XML standard document explaining why character references should be resolved before
storing the string as the value of the entity.
[MA I believe we would lose an enormous amount of expressive power and put
[JS] This may very well be true. I'm not an SGML expert.
I'd love to see an example of this. I think a good example of this would make XML parser writers much more motivated when implementing it! :-)
[MA] Recursive entity resolution is not programmatically
that much extra work
[JS] Perhaps not the resolution itself.
But making it possible to give the user good error messages (and displaying the location(s) where the error takes place) I assume is quite a lot of work. Perhaps not so for the direct coding, but to come up with the necessary architecture/design.
I also think this simpler model would make for simpler API's for tool builders, at least for tools needing to have info about where entities were invoked in the original document. (f.i. tools which updates/synchronizes documents need this info, in order to not "flatten it out".)
[MA] and allows for various important SGML facilities. And
remember that one of the explicit goals for XML is SGML compatibility.
[JS] Yes. But it would be very sad if this made XML substantially more complex (without any other benefit than compatibility), both for users and tool vendors.
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