Notes on XML, Elements, and Attributes

Published on Apr 23, 2009 (updated Feb 5, 2024), filed under development. (Share this post, e.g., on Mastodon or on Bluesky.)

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Contrary to what one might expect, I’m not bringing in much XML design experience with my occasional contributions to the HTML 5 specification. However, knowledge of the design of markup languages is something I consider beneficial for my job as a web professional as well. A few notes on XML design, inspired by internal and external documentation:

• Attributes mean more restrictions than elements. Every XML design contains some elements. An XML design that only features elements is simplest, but not necessarily most appropriate.

• Elements are handy if data are exposed to the user. If these data are not shown, using an attribute might be more useful.

• Elements should be used when information is represented that can be considered an independent object, and when there is some kind of parent and child relationship.

• Several occurrences in a data model are often better handled by elements rather than attributes. This avoids enumerated attributes like, for instance, foo1, foo2, foo3, &c.

• To order data, elements are more useful than attributes. Attributes are “inherently unordered.”

Update (November 27, 2014)

I found Uche Ogbuji’s article on principles of XML design useful, too. For example:

• The general principle of data going into elements, metadata into attributes.

• The principle of structured information: If the information is expressed in a structured form, especially if the structure may be extensible, use elements. But: If the information is expressed as an atomic token, use attributes.

• The principle of readability: If the information is intended to be read and understood by a person, use elements. But: If the information is most readily understood and digested by a machine, use attributes.

• The principle of element/attribute binding: Use an element if you need its value to be modified by another attribute.

About Me

I’m Jens (long: Jens Oliver Meiert), and I’m an engineering lead, guerrilla philosopher, and indie publisher. I’ve worked as a technical lead and engineering manager at various companies, including Google; I’m an open-source developer and a contributor to web standards (like HTML, CSS, WCAG); and I write and review books for O’Reilly and Frontend Dogma.

I love trying things, not only in web development and engineering management, but also with respect to politics and philosophy. Here on meiert.com I talk about some of my experiences and perspectives. (Please share feedback—interpret charitably, keep it friendly, but do be critical.)