Deltacode Scoring

Delta Objects

A File-Level Comparison of Two Codebases

A Delta object represents the file-level comparison (i.e., the “delta”) of two codebases, typically two versions of the same codebase, using ScanCode-generated JSON output files as input for the comparison process.

Based on how the user constructs the command-line input, DeltaCode’s naming convention treats one codebase as the “new” codebase and the other as the “old” codebase::

deltacode -n [path to the 'new' codebase] -o [path to the 'old' codebase] [...]

Basic Scoring

A DeltaCode codebase comparison produces a collection of file-level Delta objects. Depending on the nature of the file-level change between the two codebases, each Delta object is characterized as belonging to one of the categories listed below. Each category has an associated score intended to convey its potential importance – from a license/copyright compliance perspective – to a user’s analysis of the changes between the new and old codebases.

In descending order of importance, the categories are:

added: A file has been added to the new codebase.
modified: The file is contained in both the new and old codebase and has been modified (as reflected, among other things, by a change in the file’s sha1 attribute).
moved: The file is contained in both the new and old codebase and has been moved but not modified.
removed: A file has been removed from the old codebase.
unmodified: The file is contained in both the new and old codebase and has not been modified or moved.

Note

Files are determined to be Moved by looping thru the added and removed Delta objects and checking their sha1 values.

The score of a Delta object characterized as added or modified may be increased based on the detection of license- and/or copyright-related changes. See License Additions and Changes and Copyright Holder Additions and Changes below.

Delta Object Fields and Values

Each Delta object includes the following fields and values:

factors: One or more strings representing the factors that characterize the file-level comparison and resulting score, e.g., in JSON format::
```
"factors": [
  "added",
  "license info added",
  "copyright info added"
],
```
score: A number representing the magnitude/importance of the file-level change – the higher the score, the greater the change.
new: The ScanCode-based file attributes (path, licenses, copyrights etc.) for the file in the codebase designated by the user as new.
old: The ScanCode-based file attributes for the file in the codebase designated by the user as old.

Note that an added Delta object will have a new file but no old file, while a removed Delta object will have an old file but not a new file. In each case, the new and old keys will be present but the value for the missing file will be null.

License Additions and Changes

Certain file-level changes involving the license-related information in a Delta object will increase the object’s score.

An added Delta object’s score will be increased:
- If the new file contains one or more licenses (factors will include license info added).
- If the the new file contains any of the following Commercial/Copyleft license categories (factors will include, e.g., copyleft added):
  ‘Commercial’
  
  ‘Copyleft’
  
  ‘Copyleft Limited’
  
  ‘Free Restricted’
  
  ‘Patent License’
  
  ‘Proprietary Free’
A modified Delta object’s score will be increased:
- If the old file has at least one license and the new file has no licenses (factors will include license info removed).
- If the old file has no licenses and the new file has at least one license (factors will include license info added).
- If both the old file and new file have at least one license and the license keys are not identical (e.g., the old file includes an mit license and an apache-2.0 license and the new file includes only an mit license) (factors will include license change).
- If any of the Commercial/Copyleft license categories listed above are found in the new file but not in the old file (factors will include, e.g., proprietary free added).

Copyright Holder Additions and Changes

An added Delta object’s score will be increased if the new file contains one or more copyright holders (factors will include copyright info added).
A modified Delta object’s score will be increased:
- If the old file has at least one copyright holder and the new file has no copyright holders (factors will include copyright info removed).
- If the old file has no copyright holders and the new file has at least one (actors will include copyright info added).
- If both the old file and new file have at least one copyright holder and the holders are not identical (factors will include copyright change).

Moved, Removed and Unmodified

As noted above in Basic Scoring Basic Scoring, from a license/copyright compliance perspective, the three least significant Delta categories are moved, removed and unmodified.

In the current version of DeltaCode, each of these three categories is assigned a score of 0, with no options to increase that score depending on the content of the Delta object.

However, it is possible that both moved and removed will be assigned some non-zero score in a future version. In particular, removed could be significant from a compliance viewpoint where, for example, the removal of a file results in the removal of a Commercial/Copyleft license obligation.