XML Attributes vs Elements [duplicate]

Answer 1

I tend to use elements when it's data that a human reader would need to know and attributes when it's only for processing (e.g. IDs). This means that I rarely use attributes, as the majority of the data is relevant to the domain being modeled.

Answer 2

Here is another strategy that can help distinguishing elements from attributes: think of objects and keep in mind MVC.

Objects can have members (object variables) and properties (members with setters and getters). Properties are highly useful with MVC design, allowing change notification mechanism.

If this is the direction taken, attributes will be used for internal application data that cannot be changed by the user; classic examples will be ID or DATE_MODIFIED. Elements will therefore be used to data that can be modified by users.

So the following would make sense considering the librarian first add a book item (or a magazine), and then can edit its name author ISBN etc:

<?xml version="1.0" encoding="utf-8"?>
<item id="69" type="book">
    <authors count="1">
        <author>
            <name>John Smith</name>
        <author>
    </authors>
    <ISBN>123456790</ISBN>
</item>

Answer 3

The limitations on attributes tell you where you can and can't use them: the attribute names must be unique, their order cannot be significant, and both the name and the value can contain only text. Elements, by contrast, can have non-unique names, have significant ordering, and can have mixed content.

Attributes are usable in domains where they map onto data structures that follow those rules: the names and values of properties on an object, of columns in a row of a table, of entries in a dictionary. (But not if the properties aren't all value types, or the entries in the dictionary aren't strings.)

Answer 4

Personally I like using attributes for simple single-valued properties. Elements are (obviously) more suitable for complex types or repeated values.

For single-valued properties, attributes lead to more compact XML and simpler addressing in most APIs.