Re: [xml-dev] Separate the data model from presentation and makethe data

[Thomas Passin <list1@tompassin.net>]

On 11/22/2015 10:47 AM, Costello, Roger L. wrote:
> Hi Folks,
>
> Assertion: Accessing/manipulating element nodes is simpler, easier,
> and faster than accessing/manipulating text. An element-based data
> model is better suited to XML's strengths than is a text-based data
> model.
>
> Proof by example:
>
> Case 1: Retrieve "west"
>
> Text-based data model:
>
> <edge>garden west door home</edge>
>
> XPath to retrieve "west":
>
> substring-before(substring-after(., ' '), ' ')
>
> Element-based data model:
>
> <edge> <garden/> <west/> <door/> <home/> </edge>
>
> XPath to retrieve "west":
>
> *[2]/name()
>
> Clearly, retrieving "west" in the element-based data model is
> simpler, easier, and faster.
Au contraire: take for example the following

<edge>garden west door home</edge>
<edge>garage west door office</edge>

Now how will you distinguish

<edge> <garden/> <west/> <door/> <home/> </edge>
from
<edge> <garage/> <west/> <door/> <office/> </edge>
?

Clearly you have to have something stored somewhwere that will tell you 
what "garage" and "office" and "garden" and "home" are, and you will 
have to somehow know that the two "wests" have the same meaning ... if 
they do, but they might not.

Now each element name has to be stored against the element's node 
structure - as text (OK yes, could be hashed or otherwise encoded - but 
in the text node, the content also has to be stored as text (or some 
encoded version).  Now you have many more element structures but the 
same amount of text.  The text of each element name - e.g., the "west" 
names - must either be duplicated or interned, but the same can be said 
for the text content itself.

How is that supposed to be more "efficient"?  And why should it be any 
easier to process?  It all depends on what use you plan to of the data, 
and what the meaning is supposed to be.  "West garden door" might be an 
atomic label, in which case you probably want it to be stored verbatim, 
not dissassembled.

Before holding forth about processing efficiencies, and which XPATH 
expression might be "faster", it would be wise to ask the people who 
actually know how the processing is done, such as XSLT designers. 
Otherwise you are merely engaging in the equivalent of premature 
optimization.

Anyway, XML's strengths are for data interchange, not necessarily 
"processing".  If you want to emphasize small, fast data transfer, you 
could always use e.g., one of the ASN.1 binary encodings.   If you want 
to emphasize querying, you could always import into a database.

But I should stop here, since the original message sounds too much like 
a troll.

TomP

> Case 2: Retrieve a range of data items (2nd to 3rd data items)
>
> Text-based data model:
>
> <edge>garden west door home</edge>
>
> XPath to retrieve the desired range of data items:
>
> tokenize(., ' ')[position() = (2,3)]
>
> Element-based data model:
>
> <edge> <garden/> <west/> <door/> <home/> </edge>
>
> XPath to retrieve the desired range of data items:
>
> *[position() = (2,3)]/name()
>
> Clearly, retrieving a range of data items in the element-based data
> model is simpler, easier, and faster.
>
> Of course, at the point of presentation we will want to convert the
> element-based data model to a text-based data model.
>
> Recommendation: Separate the data model from presentation details and
> make data models element-based.
>
> Let's take a dramatic example. Rather than this:
>
> <living-room> you are in the living room. a wizard is snoring loudly
> on the couch. </living-room>
>
> use this as your data model:
>
> <living-room> <you/><are/><in/><the/><living-room./>
> <a/><wizard/><is/><snoring/><loudly/><on/><the/><couch./>
> </living-room>
>
> and use the former only for presentation.
>
> Do you agree?
>
> /Roger
>
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