Posted by Andy Dingley on 10/10/06 11:06

Joe wrote:

> I was spouting off the other day, telling someone the "right" (alt.html
> approved) way of doing a navigation menu.

RDF still gets this right and HTML 3.2 used to, until HTML 4 deprecated
it.

There are three container structures, which in RDF terms are Bag, Alt
and Seq.

A "bag" (an old Smalltalk term) contains a collection of things, and
that's all it really means. You can have anything in there, and you can
have more than one of each type (so it's unlike a Set). There's no
ordering.

A Seq (sequence) is like a bag, but has ordering too.

An Alt contains a set of distinct items and one is selectable from
within this list.

There's a little wooliness between these terms if you compare them
between different languages. Some see "identity" and uniqueness as
being dependent on type, others on instance. Can you put two different
objects of the same type into a set ?

In HTML terms, Bag is analogous to <ul>, Seq to <ol> and Alt to the
now-deprecated <menu>. IMHO, deprecating <menu> was an error in HTML
4 -- it's not the same thing as <ul> and it was also a useful semantic
distinction to make clear at the HTML level.

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