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RE: attributes vs. elements

• To: <xml-dev@l...>
• Subject: RE: attributes vs. elements
• From: "Alessandro Triglia" <sandro@m...>
• Date: Fri, 13 Sep 2002 16:58:51 +0200
• Importance: Normal
• In-reply-to: <20020910175146.GB846@swordfish>

> -----Original Message-----
> From: mgushee@h... [mailto:mgushee@h...] 
> Sent: Tuesday, September 10, 2002 19:52
> To: xml-dev@l...
> Subject: Re:  attributes vs. elements
> 
> 
> On Tue, Sep 10, 2002 at 01:21:37PM -0400, Maciejewski, Thomas wrote:
> > This is sort of a newbie question but one that I never 
> fully understood or
> > maybe just don't know how to explain it to others. 
> > 
> > When should one use an element and when should one use an attribute?
> 
> That's a very common and very important question, and it's probably in
> a FAQ somewhere, but I have no idea which FAQ. In any case, 
> there is no
> hard and fast answer to that question.
> 
> The traditional distinction between elements and attributes 
> is that the
> former are for content (information of interest to the end user or the
> consuming application) and the latter for metadata (information about
> information), and there is no clearcut, universal distinction between
> those two. Generally speaking, the text in a paragraph or the 
> data in a
> database record would be considered content; the date that content was
> last modified will probably be metadata, but it's not hard to imagine
> scenarios where you might want to treat it as content. Ultimately,
> deciding whether something is content or metadata is up to 
> the creators
> and users of the information.
> 
> But back to elements and attributes. Some considerations that 
> may affect
> your choice:
> 
>   * Elements may not have more than one attribute with the same name, 
>     but child element names can be repeated indefinitely (unless 
>     forbidden by a schema, of course).
> 
>   * XML parsers must preserve the order of elements, but not 
> attributes.
> 
>   [ given the above two statements, we can say that in programming
>     terms, the attributes of any given element are analogous to a 
>     hash (AKA mapping, dictionary, etc.), while the child elements 
>     are analogous to an array ]
> 
>   * Attributes can't contain elements--though of course they can
>     reference them.
> 
>   * White space in elements can be preserved, whereas white space in
>     attributes is normalized (leading and trailing spaces are 
> stripped,
>     each extent of internal white space is collapsed to a single space
>     character).

Matt,

I don't follow you.  If the schema is specified in XML Schema and the
datatype of an attribute is "string" (whose "whitespace" facet is
"preserve" by default), I don't believe white space is normalized.  Are
you saying that an attribute of type "string" behaves differently from
an element of type "string" as to white space handling?

Alessandro Triglia



> 
>   * Attributes are more compact, since their names only occur once per
>     instance and they have fewer 'overhead' characters: ="" 
> vs. <> </>.
> 
>   * Many people find elements more readable.
> 
> I think there is a tendency for document-oriented 
> applications to prefer
> elements, and messaging and automated data-exchange applications to
> prefer attributes--the rationale being that bandwidth is more 
> important
> and human-readability less so. However, in cases where 
> human-readability
> is unimportant, you might want to ask whether XML is an appropriate
> solution at all.
> 
> That's my $.02.
> 
> -- 
> Matt Gushee
> Englewood, Colorado, USA
> mgushee@h...
> http://www.havenrock.com/
> 
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    • From: Matt Gushee <mgushee@h...>

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