Is there any specific name for strings of data that have well defined format ? For example URLS, domain names, IP Addresses, Email addresses, File Paths etc. are all having well defined delimiters and data formats. What are these special strings in general called ?

  • 1
    $\begingroup$ I would call an URL an URL, an IP address an IP address, and so on. Is that not possible, or why are you insisting on an umbrella term? $\endgroup$
    – Juho
    Commented Apr 10, 2014 at 12:49
  • $\begingroup$ am designing some algorithms for these special strings. i need some word to collectively addressing them than specifically calling URLs, IPs etc. $\endgroup$
    – sashank
    Commented Apr 10, 2014 at 12:57

2 Answers 2


Any set of strings is a (formal) language. That's probably not what you mean since you have quite specific restrictions in mind.

Many standardised string formates are defined by regular expressions what makes the respective sets of strings they admit regular languages. Note that some examples are actually finite languages (IPs).

In then end, it depends on what you mean by "well defined". Any set of strings is well-defined. Anything more will depend on the kind of specification you give, and then the language will (sort of) inherit the specification's "name".


These strings are called, if I may say, standard notations.

They are all defined in standard documents, some of which are sometimes updated, replaced by newer ones. When the Internet is concerned, many of these documents are produced by the Internet Engineering Task Force (IETF) under the strange name of "Request for Comments" (RFC). The syntax is usually given by context-free grammars, sometimes extended with regular expressions, in some appropriate notation (even though these formats are often regular languages).

URLS are defined in RFC 1738 (complemented by RFC 3986)

URLs are actually a very complex, and somewhat open, format, described syntactically in section 5 of RFC 1738. The definition make use of other standardized formats.

For example, Email addresses are defined by RFC 822, and this definition is used in the definition of URls such as "mailto:xxx@yyy"

Regarding file paths, you have definitions, notations, and semantics that are specific to operating systems. But there is also an internet wide notation and semantics that is part of the definition of URLs in RFC 1738.

Regarding domain names, the oldest non obsolete RFC defining them is RFC 1035. Their accepted syntax in URLs is defined in section 5 of RFC 1738.

Similarly IP addresses are currently standardized by RFC 1918 for IPv4 and RFC 2460 for IPv6, and the syntax is used for URLs.

When looking for such a definition, adding "RFC" to the keywords will usually get you faster to the right place (when Internet is concerned).

And in case you worry about electricity shortage, there is also a standard format, and the corresponding RFC, to send mail by homing pigeon. See RFC 1149.


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