What is the significance/reason for the "I" prefix in front of Novus GUIDs?

What is the significance/history behind the "I" prefix used on Novus GUIDs?

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Greg is correct on why we need a letter as the first character of the guid. As for the letter "I" I believe it originally stood for Identifier and was simply used as a standard convention. In reality, that first letter can be whatever we want it to be and there are a few systems that have used variant letters for specific tracking reasons. However, just because you can use any other letter does not mean that you should. You should have a definitive reason for wanting to break from the standard as the guid should ideally have no implied meaning.

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Randy Aldrich

I is the most common, but is not required. I've seen F,D and several others. In addition the 33 character length is also not required. It simply needs to begin with a letter and bet AT MOST 33 characters.

Greg Bender

I've always thought the letter prefix was used so that GUIDs could appear in XML element or attribute names, which can't start with a number. Not sure why I is more common than other letters though.

troy.hanisch

mtaylor

While element and attribute names can't begin with a number, element and attribute values can. When would we ever use a GUID as an element/attribute name?

troy.hanisch

I probably misspoke a bit. In order for an attribute to be considered as type ID or IDREF in the DTD or Schema it's value must start with a letter. So if you think about a simple example such as a footnote then you have an ID on the footnote itself and an IDREF on the footnote reference.

Ed Brannin

@Troy Perhaps you could update your answer to reflect that [letter-first restriction](http://www.w3.org/TR/1999/REC-xml-names-19990114/#NT-NCName) for [ID & IDREF attributes](http://www.w3.org/TR/xmlschema-2/#ID)?

Kajsa Anderson

I've also seen some with an R prefix

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