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   RE: A practical question about attributes

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  • From: "Jeffrey E. Sussna" <jes@kuantech.com>
  • To: "'Tim Bray'" <tbray@textuality.com>,"'XML-DEV'" <xml-dev@ic.ac.uk>
  • Date: Tue, 12 Jan 1999 15:07:35 -0800

In general I try not to warp my designs to save bytes; in this case, however, I'm on the edge of being able to justify using XML as opposed to a hardwired data format, for performance reasons. However, it turns out Tim is absolutely right. I generated some sample data using elements and then using attributes. Uncompressed, the file sizes in bytes were 8341 (elements), 5041 (attributes). After being zipped, though, the sizes were 1085 (elements), 989 (attributes). Assuming I can do the zip and unzip within the timing constraints (I'm pretty sure I can), then I think XML in general and the elements approach in particular will work.

Thanks Tim!


-----Original Message-----
From: Tim Bray [mailto:tbray@textuality.com]
Sent: Tuesday, January 12, 1999 12:24 PM
To: Jeffrey E. Sussna; 'XML-DEV'
Subject: Re: A practical question about attributes

At 11:38 AM 1/12/99 -0800, Jeffrey E. Sussna wrote:
>I can gain significant size reductions by representing things as attributes 
>rather than sub-elements. Here is an example:

In general, I'd say it's a bad practice to warp your design out of
shape in order to save bytes; LZ compression does a better job anyhow.

><session id="25" type="Q" num="15"/>

Let's take a closer look, at "<id>25</id>" vs id='25'.  In this case,
you're only saving 4 chars.  Attributes carry 3 characters of overhead: 
equals and two quotation marks, beyond the name.  If the length of the 
name is N, then elements carry N + 5 (end tag, <, >, </, >).  So the 
saving is N+2 chars, where N is the length of the name.  Work it out.

>Here's the question: does anyone know of any gotchas in using attributes 
>instead of elements? Parsing issues, etc.?

Yeah, they can't repeat, they can't have internal structure, they can't
contain external entities, they have no defined order.  But perhaps
these aren't material in your application. -T.

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