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- From: Toby Speight <firstname.lastname@example.org>
- To: "XML developers' list" <email@example.com>
- Date: 18 Dec 1997 16:32:39 +0000
Peter> Peter Murray-Rust <URL:mailto:firstname.lastname@example.org>
> In article <email@example.com>,
> Peter wrote:
Peter> Is it the question of the return value of a non-existent
Peter> attribute. IOW what does
Peter> <!ATTLIST FOO PLUGH CDATA #IMPLIED>
Peter> <FOO BAR="baz" XYZZY="" BLORT="six spaces"/>
Peter> return for
Peter> String s = element.getAttval("PLUGH");// could be "", or null
David has answered the original question (what is isSpecified() for in the
Java simple API?), but I thought I'd mention that DSSSL's attribute-string
function returns #f for PLUGH; the Java equivalent of this is of course,
null. I think this is the Right Thing to do; it's sometimes important to
tell the difference between <Fu bargh=""/> and <Fu/>.
The first case is often used to mean a known, empty value; the second
to mean "not known" or "not applicable".
Concrete example: I'm a rock climber, and I keep a record of all my
climbing in XML format. Climbs are defined as
climbs.dtd> <!ELEMENT climb (#PCDATA)>
climbs.dtd> <!ATTLIST climb
climbs.dtd> grade CDATA ""
climbs.dtd> stars CDATA #IMPLIED
climbs.dtd> style (l|2|al|s|tr|mt) #IMPLIED
climbs.dtd> with CDATA #IMPLIED
Note the "stars" attribute, which is used for a climb's star rating
(an indication of quality). An instance looks like
climbs.xml> <climb grade="VD" stars="" style="2"
climbs.xml> with="&p-hkm;">Difficult Crack</climb>
Here, the lack of stars is explicit - it's not a high-quality climb.
climbs.xml> <climb grade="D" with="&p-ejk;, &p-dmj;"
climbs.xml> style="l">King's Chimney</climb>
is a climb in a part of Britain where the star system isn't used, and
so I omitted the attribute - even though it probably deserves a star
I would not want these two values confused!
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