The ROUGE (Recall-Oriented Understudy for Gisting Evaluation) metric is one of the Classic Metric Type Galtea exposes to evaluate how well a generated summary captures the content of a reference summary. It is primarily used for summarization tasks and other scenarios where recall is more important than exact lexical match.

​
Evaluation Parameters

To compute the rouge metric, the following parameters are required:
  • actual_output: The model’s generated summary.
  • expected_output: The reference (or gold) summary to compare against.

​
How Is It Calculated?

This implementation uses ROUGE-L, which focuses on the Longest Common Subsequence (LCS) between the candidate and reference:
  1. Longest Common Subsequence
    Identifies the longest sequence of words that appears in both candidate and reference (not necessarily contiguous, but in the same order).
  2. Precision & Recall
    • Precision (P) = LCS length / candidate length
    • Recall (R) = LCS length / reference length
  3. F1 Score
    Combines precision and recall:     F1=2⋅P×RR+PF1 = 2 \cdot \frac{P \times R}{R+P}
ROUGE-L returns a score between 0 and 1:
  • ≥ 0.5 – Strong overlap with the reference summary.
  • 0.3 – 0.5 – Moderate overlap; acceptable for abstractive summarization.
  • < 0.3 – Weak overlap; likely missing key content.

​
Suggested Test Case Types

Use ROUGE when evaluating:
  • Abstractive or extractive summaries.
  • Headline generation where recall of important tokens matters.
  • Content coverage tests for long text generation.