erdi8 0.1.0

Count according to lower case alphabet and numbers (without ambiguous 0, 1, and l) and always start with a letter

erdi8

erdi8 is a unique identifier scheme and counter that operates on the following alphabet:

['2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 
'i', 'j', 'k', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

It is basically a base36 alphabet that intentionally avoids the ambiguous characters [0, 1, and l] and therefore shrinks to 33. In addition to that, it ensures that no identifier starts with a numeric value by using an offset of 8. The zero is represented by 'a', 25 is represented by 'a2', etc. With three characters or less one can create 28'075 (25 + 25 * 33 + 25 * 33 * 33) different identifiers. With 6 characters or less we have 1'008'959'350 options. In a traditional identifier world, one would use a prefix, e.g. M, and then an integer. This only gives you 100k identifiers (M0 to M99999) with up to 6 characters. The scheme enables consecutive counting and is therefore free of collisions. In particular, it is not a method to create secret identifiers.

Usage

Basic

$ python3

>>> from erdi8 import Erdi8
>>> e8 = Erdi8()
>>> e8.increment("erdi8")
'erdi9'
>>> e8.decode_int("erdi8")
6545185
>>> e8.encode_int(6545185)
'erdi8'

Advanced

Fixed length "fancy" identifiers with safe=True

$ python3

>>> from erdi8 import Erdi8
>>> safe = True
>>> start = 'b222222222'
>>> seed = 453459956896834
>>> e8 = Erdi8(safe)
>>> e8.increment_fancy(start, seed)
'fmzz7cwc43'
>>> current = e8.increment_fancy('fmzz7cwc43', seed)
>>> print(current)
k7zydqrp64

NOTE

0. These sequences may have a fancy appearance but they are not random. They are perfectly predictable and are designed to "fill up the whole mod space" before previously coined identifiers start re-appearing.
1. The safe=True option helps you to avoid unintended words (i.e. removes the characters [aeiou] from the alphabet)
2. The fancy increment works with fixed lengths. If you work with a length of 10 (like above) You will have 20 * 28^9 = 211'569'119'068'160 options with safe=True. If you think you have more things to identify at some point you have two options: a) start directly with more characters or b) check for the start value (in this case b222222222) to re-appear - this will be the identifier that will "show up twice" first.
3. Store the following four parts in a safe place: a) safe parameter b) the start value c) the seed value. On top, keep good track of the current value.

Test cases

$ python3 -m unittest test/erdi8_test.py 

Intended use

When you run an identifier redirect service of the type https://purl.example.org/ your users can reserve "their space" for their current business application and or domain. We encourage the administrator of such a service to offer opaque folder names for long-term identifier stability. These folder names can be chosen to follow the erdi8 scheme and offer 825 (25 * 33) potential two-character folder names. In addition, also subfolder names and local accession identifiers can be generated with this scheme such that FAIR data objects can be identified with URIs of the type https://purl.example.org/b7/a/erdi8.

FAQ

Why no upper case characters?

Because we don't want to erdi8 to be confused with Erdi8.

Why no start with a number?

Because we want to avoid "number-only" identifiers. If we allowed to start with a number, we would have identifiers of the type 42 and 322 which could be mistaken for integers. We could achieve this with a more complex scheme avoiding any number-only combinations (would therefore still allow ids like 2z, to be investigated).

How about combinations that form actual (bad) words?

This depends on the use case and the way erdi8 is used. Therefore, we can recommend to work with filter lists. In addition, an erdi8 object that avoids the aeiou characters can be created with Erdi8(safe=True). This shrinks the available character space to 28 and the produced output is not compatible to Erdi8(safe=False) (default). The danger that unintended English words are created is lower with this setting. It is recommended for erdi8 identifiers that are longer than three characters where filter lists start to become impractical.

How does this relate to binary-to-text encodings such as base32 and base64?

erdi8 can be used for a binary-to-text encoding and the basic functions to implement this are provided with encode_int and decode_int. However, the primary purpose is to provide a short counting scheme for identifiers.