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ISCC-UNIT Data-Code#

IEP: 0008
Title: ISCC-UNIT Data-Code
Author: Titusz Pan tp@iscc.io
Comments: https://github.com/iscc/iscc-ieps/issues/13
Status: DRAFT
Type: Core
License: CC-BY-4.0
Created: 2022-09-28
Updated: 2024-11-30

Note

This document is a DRAFT contributed as input to ISO TC 46/SC 9/WG 18. The final version is published under ISO 24138:2024.

1. General#

  1. The Data-Code shall be a similarity hash for any kind of data regardless of its media type.
  2. The Data-Code shall cluster digital assets that have near-identical data.
  3. Small differences (as a proportion of the whole) in referent data shall yield identical Data-Codes.
  4. More significant differences in referent data shall produce similar Data-Codes that can be compared against each other to estimate the data-similarity of the referents.
  5. The Data-Code shall be resistant to data shifting and reordering sequences of data within referent data.

NOTE

Changes of the Data-Code do not reflect semantic or syntactic changes of the content.

2. Format#

The Data-Code shall have the data format illustrated in Figure 10:

Figure 10 - Data format of the Data-Code

Figure 10 - Data format of the Data-Code

EXAMPLE 1: 64-bit Data-Code in its canonical form:

ISCC:GAAWAIBQLNWP7X32

EXAMPLE 2: 256-bit Data-Code in its canonical form:

ISCC:GADWAIBQLNWP7X32J3INMAMDUJ4QMN67BBQKVTVZIWHXQ7QJIKHYTBY

3. Inputs#

The input for calculating the Data-Code shall be the bytes of a file, without reference to their meaning or structure.

4. Outputs#

Data-Code processing shall generate the following output elements:

  • iscc: the Data-Code in its canonical form (required).

5. Processing#

An ISCC processor shall calculate the Data-Code as follows:

  1. Split the data into variable sized chunks with an average chunk size of 1024 bytes using the content defined chunking (CDC) algorithm.
  2. Calculate the 32-bit integer hash of each chunk using the XXH32 algorithm.
  3. Apply the minhash algorithm to the array of 32-bit integers to calculate the ISCC-BODY of the Data-Code with appropriate length.

NOTE

For further technical details see source-code in modules code_data.py and minhash.py of the reference implementation.

6. Conformance#

An implementation of the Data-Code algorithm shall be regarded as conforming to the standard if it creates the same Data-Code as the reference implementation for the same data input.

NOTE

The ISCC reference implementation uses the open source XXHASH library 1 for XXH32 chunk hashing and appropriate use of this software will generate the same codes as the reference implementation.

7. Bibliography#

  1. Collet, Yann. xxHash: Extremely fast hash algorithm.
    Accessed July 2022, available at https://cyan4973.github.io/xxHash/ ↩