Paraphrase Mining

Paraphrase mining is the task of finding paraphrases (texts with identical / similar meaning) in a large corpus of sentences. In Semantic Textual Similarity we saw a simplified version of finding paraphrases in a list of sentences. The approach presented there used a brute-force approach to score and rank all pairs.

However, as this has a quadratic runtime, it fails to scale to large (10,000 and more) collections of sentences. For larger collections, the paraphrase_mining() function can be used:

from sentence_transformers import SentenceTransformer
from sentence_transformers.util import paraphrase_mining

model = SentenceTransformer("all-MiniLM-L6-v2")

# Single list of sentences - Possible tens of thousands of sentences
sentences = [
    "The cat sits outside",
    "A man is playing guitar",
    "I love pasta",
    "The new movie is awesome",
    "The cat plays in the garden",
    "A woman watches TV",
    "The new movie is so great",
    "Do you like pizza?",
]

paraphrases = paraphrase_mining(model, sentences)

for paraphrase in paraphrases[0:10]:
    score, i, j = paraphrase
    print("{} \t\t {} \t\t Score: {:.4f}".format(sentences[i], sentences[j], score))

The paraphrase_mining() accepts the following parameters:

sentence_transformers.util.paraphrase_mining(model, sentences: list, show_progress_bar: bool = False, batch_size: int = 32, query_chunk_size: int = 5000, corpus_chunk_size: int = 100000, max_pairs: int = 500000, top_k: int = 100, score_function: Callable[[torch.Tensor, torch.Tensor], torch.Tensor] = <function cos_sim>) → list

Given a list of sentences / texts, this function performs paraphrase mining. It compares all sentences against all other sentences and returns a list with the pairs that have the highest cosine similarity score.

Parameters

• model (SentenceTransformer) – SentenceTransformer model for embedding computation

• sentences (List[str]) – A list of strings (texts or sentences)

• show_progress_bar (bool, optional) – Plotting of a progress bar. Defaults to False.

• batch_size (int, optional) – Number of texts that are encoded simultaneously by the model. Defaults to 32.

• query_chunk_size (int, optional) – Search for most similar pairs for #query_chunk_size at the same time. Decrease, to lower memory footprint (increases run-time). Defaults to 5000.

• corpus_chunk_size (int, optional) – Compare a sentence simultaneously against #corpus_chunk_size other sentences. Decrease, to lower memory footprint (increases run-time). Defaults to 100000.

• max_pairs (int, optional) – Maximal number of text pairs returned. Defaults to 500000.

• top_k (int, optional) – For each sentence, we retrieve up to top_k other sentences. Defaults to 100.

• score_function (Callable[[Tensor, Tensor], Tensor], optional) – Function for computing scores. By default, cosine similarity. Defaults to cos_sim.

Returns

Returns a list of triplets with the format [score, id1, id2]

Return type

List[List[Union[float, int]]]

To optimize memory and computation time, paraphrase mining is performed in chunks, as specified by query_chunk_size and corpus_chunk_size. To be specific, only query_chunk_size * corpus_chunk_size pairs will be compared at a time, rather than len(sentences) * len(sentences). This is more time- and memory-efficient. Additionally, paraphrase_mining() only considers the top_k best scores per sentences per chunk. You can experiment with this value as an efficiency-performance trade-off.

For example, for each sentence you will get only the one most relevant sentence in this script.

paraphrases = paraphrase_mining(model, sentences, corpus_chunk_size=len(sentences), top_k=1)

The final key parameter is max_pairs, which determines the maximum number of paraphrase pairs that the function returns. Usually, you get fewer pairs returned because the list is cleaned of duplicates, e.g., if it contains (A, B) and (B, A), then only one is returned.

Note

If B is the most similar sentence for A, A is not necessarily the most similar sentence for B. So it can happen that the returned list contains entries like (A, B) and (B, C).