Hi Folks,
DEFINITION - VISIBLE WEB
By “visible Web” I
mean the portion of the Web that produces information intended for human consumption.
In particular, in this message I will focus on the portion of the Web that
produces information to be consumed by humans via a browser.
DEFINITION – HIDDEN WEB
The “hidden Web”,
on the other hand, is the portion of the Web that produces the information intended
to be consumed by machines (i.e., machine-to-machine
interaction).
USING XML ON THE VISIBLE WEB VERSUS NOT
USING XML ON THE VISIBLE WEB
Below are two examples to demonstrate
what I mean by using XML on the visible Web versus not using XML on the visible
Web.
Note:
I realize that XHTML is XML, but for this discussion when I refer to “XML” I am not
referring to XHTML.
EXAMPLE: USING XML ON THE VISIBLE WEB
Suppose that you have a Web site where
you make available your grocery list to anyone with a browser. “Using XML on
the visible Web” means that you create an XML document
that contains the raw grocery list, and a separate document (e.g., XSLT) which transforms the raw
grocery list into a visually appealing form. Here is grocery.xml:
<?xml version=“1.0”?>
“
<?xml-stylesheet
type=“text/xsl” href="“grocery.xsl”?>
<grocery-list>
<fruit>Orange</fruit>
<meat>Chicken</meat>
<vegetable>Corn</vegetable>
</grocery-list>
Here is the URL to your grocery list
resource:
http://www.example.org/food/grocery-list
A browser client that issues this URL
will receive grocery.xml, and then it will dynamically transform the XML into HTML
using grocery.xsl
Let’s imagine that grocery.xsl
displays the grocery items as an unordered bulleted list, and so the XML is
rendered by the browser like this:
Your Web site is employing XML on the
visible Web!
EXAMPLE: NOT USING XML ON THE
VISIBLE WEB
Now let’s contrast the above
example with not using XML on the visible Web, instead, using HTML. A browser
client that issues the above URL will receive from your Web site this HTML:
<HTML>
<body>
<ul>
<li>Orange</li>
<li>Chicken</li>
<li>Corn</li>
</ul>
</body>
</HTML>
The browser immediately renders the
HTML. The same bulleted list shown above is displayed.
Your Web site is not employing
XML on the visible Web!
ADVANTAGES OF USING XML ON THE VISIBLE
WEB
1. The tags <grocery-list>, <fruit>, <meat>, <vegetable> are more “semantically rich” than the tags <ul> and <li>. Thus, it seems plausible that a
search tool could recognize that the above XML document is not relevant to a
query for, say, orange cars. But the search tool would not be able to
recognize that the above HTML document is not relevant. So, using XML on
the visible Web has the potential to facilitate more accurate searches.
2. The job of styling the information is
offloaded to the clients. The Web server is relieved of the
transformation burden and thus can potentially process more requests.
ASSERTION #1
There
is little usage of XML on the visible Web.
Below are several assertions which
attempt to explain why there is little usage of XML on the visible Web.
ASSERTION #2
There
is not the necessary “critical mass” of browsers which support the styling
of XML using either CSS or XSLT.
ASSERTION #3
Advantage
1 listed above is a myth, i.e., <grocery-list>, <fruit>, <meat>, <vegetable> is not more “semantically rich” than <ul> and <li>. In fact, the opposite is the case.
The tags <ul> and <li> have clear semantics (i.e., an unordered list of items) that are understood by
every browser on the planet. Conversely, <grocery-list>, <fruit>, <meat>, <vegetable> have vague semantics, are understood only by
English-speaking people, and probably zero applications on the visible Web would
be able to do anything useful with the tags or the data within the tags.
ASSERTION #4
Advantage
2 listed above is also an advantage of HTML, i.e.,
the data is contained in an HTML document and the presentation instructions are
contained in a separate CSS document.
ASSERTION #5
XML
is not appropriate for the visible Web. XML will continue to have limited
usage on the visible Web. As Len Bullard says, “XML is plumbing”.
ASSERTION #6
On
the visible Web, HTML will continue to be the primary markup language for the
foreseeable future.
QUESTION #1
Which assertions do you accept, and
which do you reject? For those assertions you reject, why?
QUESTION #2
Suppose that you are in charge of a Web
(you control the funding of all the Web sites). Would you issue this
mandate to all the Web site developers: “All information on the
visible Web must be in XML”? If you would issue this
mandate, why?
QUESTION #3
Do you think that XML should have a more
prominent role on the visible Web? If so, how would you stimulate greater
usage of XML on the visible Web?
/Roger
