CODEWITHSUNDEEP
xsdintegerw3cspecifications
pjanssen
pjanssen

Reputation: 1111

Why does the W3C XML Schema specification allow integers to have leading zeros?

Recently I had an example where in a xml message integer fields contained leading zeros. Unfortunately these zeros had relevance. One could argue why in the schema definition integer was chosen. But that is not my question. I was a little surprised leading zeros where allowed at all. So I looked up the specs which of course told me the supertype is decimal. But as expected specification don't really tell you why certain choices where made. So my question is really what is the rationale for allowing leading zeros at all? I mean numbers generally don't have leading zeros.

On a side note I guess the only way to add a restriction on leading zeros is by a pattern.

Upvotes: 3

Views: 2181

Answers (2)

C. M. Sperberg-McQueen
C. M. Sperberg-McQueen

Reputation: 25034

My recollection is that the XML Schema working group allowed leading zeroes in XSD decimals because they are allowed in normal decimal notation: 1, 01, 001, 0001, etc. all denote the same number in normal numerical notation. (But I don't actually remember that it was discussed at any length, so perhaps this is just my reason for believing it was the right thing to do and other WG members had other reasons for being satisfied with it.)

You are correct to suggest that the root of the problem is the use of xsd:integer as a type for a notation using strings of digits in which leading zeroes are significant (as for example in U.S. zip codes); I think you may be over-generous to say that one could argue about that decision. What possible arguments could one bring forward in favor of such an obviously erroneous choice?

Upvotes: 5

Guffa
Guffa

Reputation: 700152

Although numbers often doesn't have leading zeroes, parsing numbers almost always allows leading zeroes.

You don't want to disallow leading zeroes for numbers completely, because you want the option to write a number like 0.12 and not only like .12. As you want to allow at least one leading zero for floating point numbers, it would feel a bit restrictive to only allow one leading zero, and only for floating point numbers.

Sometimes numbers do have leading zeroes, for example the components in a date in ISO8601 format; 2014-05-02. If you want to parse a component it's convenient if the leading zero is allowed, so that you don't have to write extra code to remove it before parsing.

The XML specification just uses the same sets of rules for parsing numbers that is generally used for most formats and in most programming languages.

Upvotes: 2

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