Should I encode data as XML attributes or child nodes

This question pops up quite commonly: should I encode my AJAX data as XML attributes or as child tags with actual value in the text of the tag? The answer, as always, depends on your data structure:

• If your data is simple and non-hierarchical (for example, results of SQL query), using XML attributes will reduce the response size (due to shorter markup)
• If you have repeating values in your data set, you cannot use attributes, as XML allows only a single attribute with a certain name per tag. In this case, you have to use child tags to encode repeating values. However, you can still transfer the actual value as an attribute of the child tag, not as text in the tag.
• If you're transfering large character fields, using child tags will increase the readability of the XML response when you're inspecting it with a browser (you know, sometimes we have to do a bit of debugging :)
• You might hit platform-dependent limitations if you use long attribute values, so yet again you would be better off using child nodes in this case
• Obviously, you cannot use CDATA section in an attribute, the attribute value has to be properly quoted.

This post is part of You've asked for it series of articles.