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RE: [xsl] Converting CSV to XML without hardcoding schema details in xsl

2006-06-24 00:41:22

There's a lot of potential backtracking here: it might be better to 
replace each "(.*)," with "[^,]*" or with "(.*?),".

[Pantvaidya, Vishwajit] Does "[^,]*" work the same as "(.*)," 
- I understand that ^ is start of line metachar. How does the 
former match the alphabet chars?

No, within square brackets, ^ means "not". So [^,]* matches a sequence of
any characters except comma.

The problem with your expression is that (.*) matches as many characters as
it can. Then it sees ",", so it backtracks to find the last comma. Then it
sees the next (.*), and has to backtrack again; and so on.


My own instinct would be to use something like:

([^"]*,|"[^"]*",)*


[Pantvaidya, Vishwajit] Oxygen would not accept this regex as 
"it matches a zero-length string".

Perhaps then you want to change the final "*" to a "+".

Anyway, how does this regex work - it does not seem to have 
anything that matches the alphabet chars.

See above: [^"] matches everything except quotes.

And does the ,|" match comma or double quotes - because 
actually some field will have both.

The first alternative, [^"]*, matches any field that ends with a comma, and
doesn't contain a quotation mark. The second alternative, "[^"]*,", matches
any field that begins and ends with quotes (followed by a comma), and might
contain a comma between the quotes.

It's very hard to find out what the exact rules for CSV files used by a
particular product are: for example, how it represents a field that contains
quotation marks as well as commas. (That's one of the great advantages of
XML< you can find a specification!) If you know the exact rules for your
particular flavour of CSV, you can adapt the regex to match (well, you can
if you study a bit more about regular expressions).


Maybe this conversion is easier done with some Java code.

I'm sure it can be done using regular expressions but it looks as if you
need to do some learning in this area.

Michael Kay
http://www.saxonica.com/


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