Best practices: XML attribute vs XML element - When should I use elements and when should I use attributes? [duplicate]

Answer 1

The first alternative scales a bit better. Suppose that you need to add another attribute of an animal section, such as the status of the section. I suggest that this representation:

<sitemap>
  <category name="Animals">
    <section title="Dogs" status="draft">
      ...
    </section>
  </category>
</sitemap>

does a better job of conveying the following facts:

1. name is a property of the category
2. a category could have multiple sections
3. status is a property of a section; not all sections in the category are required to have the same status.

In short, it makes the hierarchical structure clearer, and shows which attributes apply at each level of the hierarchy.

Answer 2

I think that the answer is quite obvious when you think about how you want to add more dogs:

<sitemap>
  <category name="Animals">
    <section title="Dogs">
      <page url="/pics/greatdane.jpg" title="Great Dane"/>
      <page url="/pics/wienerdog.jpg" title="Wiener Dog"/>
    </section>
  </category>
</sitemap>

or

<sitemap>
  <page>
    <category>Animals</category>
    <section>Dogs</section>
    <title>Great Dane</title>
    <url>/pics/greatdane.jpg</url>    
  </page>
  <page>
    <category>Animals</category>
    <section>Dogs</section>
    <title>Wiener Dog</title>
    <url>/pics/wienerdog.jpg</url>
  </page>
</sitemap>

Answer 3

I use elements for data and attributes for Metadata

Answer 4

I prefer the second. Elements should be used to describe data (which is mostly what you are doing). Attributes are used for values not relevant to the data, such as the max size for an element for example.

Answer 5

XML is horrible file format and ends up in religious wars. Do whatever you feel is best at the time, provided you can justify it. However, your particular examples are significantly different:

In 1, sitemap encapsulates a category encapsulating a section which encapsulates the page.

In 2, sitemap encapsulates a page which encapsulates three items: category, section, title and URL. None of these three items contains any other, they are siblings, all commonly held within the page.

As two different structures, it depends on which you intended.

A different question would be the preference for attributes versus first-level tags. But as I say, that is a different question!

Answer 6

The issue of attributes vs elements has been around for the better part of a decade and there is no right answer. Instead consider the differences and from that you should be able to decide which to use:

• There can be only one instance of an attribute although you can enforce this with elements using DTD or XML Schema;
• Attributes are unordered. Elements are not;

• Attributes lead to a more concise syntax if there are no children. Compare:

  <page name="Sitemap"/>

to:

<page>
  <name>Sitemap</name>
</page>

I know which one I prefer;

• Not really relevant now since DTDs aren't used much (if at all) over XML Schema but I'll add it anyway: DTDs allow default values (implied) for attributes but no such mechanism for elements; and
• Elements, being elementss, can have children and attributes of their own. Attributes obviously cannot.

So, from your example, your innermost <page> element has a URL attribute (although it's an image for some reason--perhaps a preview icon? If so the attribute name is misleading). A webpage only has one URL (generally) so that'd be a good example of something that could be an attribute.

If on the other hand you wanted to list the images on the page, there could obviously be more than one so you'd need elements for that.

But, in the end, most of the time there's no right or wrong answer and it's largely a question of style.