Building semantic search with SentenceTransformers on AMD#

In this blog, we explain how to train a SentenceTransformers model on the Sentence Compression dataset to perform semantic search. We use the BERT base model (uncased) as the base transformer and apply Hugging Face PyTorch libraries.

Our goal in training this custom model is to use it for performing semantic search. Semantic search is an information retrieval method that understands the intent and context of a search query, rather than simply matching keywords. For example, searching for apple pie recipes (the query) would return results (the documents) about how to make apple pie, not just pages containing the words apple and pie.

You can find files related to this blog post in the GitHub folder.

Introduction to SentenceTransformers#

Training a SentenceTransformers model from scratch involves a process where the model is taught to understand and encode sentences into meaningful, high-dimensional vectors. In this blog, we focus on a dataset that contains pairs of equivalent sentences. Overall, the training process aims to have the model learn how to map semantically similar sentences, which are close to each other within a vector space, while moving the dissimilar ones farther apart. In contrast to generic pre-trained models, which might not be able to capture the specificities of certain domains or use cases, a custom trained model ensures that the model is finely tuned to understand the context and semantics relevant to a particular domain or application.

We’re interested in performing asymmetric semantic search. In this approach, the model acknowledges that the query and the documents can be different in nature. For example, having short queries and long documents. Asymmetric semantic search uses encodings that make search more effective, even when there’s a disparity in the type or length of text. This is useful for applications like information retrieval from large documents or databases where queries are often shorter and less detailed than the content that they are searching through. Here’s an example of how semantic search works:

Query: Is Paris located in France?

Most similar sentences in corpus:
The capital of France is Paris (Score: 0.6829)
Paris, which is a city in Europe with traditions and remarkable food, is the capital of France (Score: 0.6044)
Australia is known for its traditions and remarkable food (Score: -0.0159)

Implementation on an AMD GPU#

This blog has been tested on ROCm 6.0 and Pytorch 2.0.1 versions.

To get started, first install these prerequisites:

  1. ROCm for Linux

  2. Latest PyTorch Docker image

Run the PyTorch Docker container with:

docker run -it --cap-add=SYS_PTRACE --security-opt seccomp=unconfined --device=/dev/kfd --device=/dev/dri --group-add video --ipc=host --shm-size 8G rocm/pytorch:latest

Let’s describe some the options for the command used to start the container:

  • -it: This combination of -i and -t allows to interact with the container through the terminal.

  • --device=/dev/kfd --device=/dev/dri: These options give access to specific devices on the host. --device=/dev/kfd is associated with AMD GPU devices and --device=/dev/dri is related to devices with direct access to the graphics hardware.

  • --group-add=video: This option allows the container to have necessary permissions to access video hardware directly.

  • rocm/pytorch:latest: This is the name of the latest PyTorch Docker image.

The rest of the options configure security options, grant more privileges and adjust resource usage.

Then install the following Python packages:

!pip install datasets ipywidgets -U transformers sentence-transformers

Importing Python packages#

from datasets import load_dataset
from sentence_transformers import InputExample, util
from torch.utils.data import DataLoader
from torch import nn
from sentence_transformers import losses
from sentence_transformers import SentenceTransformer, models

The dataset#

The Sentence Compression dataset consists of 180,000 pairs of equivalent sentences. These sentence pairs demonstrate how a longer sentence can be compressed into a shorter one, while retaining the same meaning.

Preparing the dataset#

dataset_id = "embedding-data/sentence-compression"
dataset = load_dataset(dataset_id)

Let’s explore one sample in the dataset:

# Explore one sample
print(dataset['train']['set'][1])
['Major League Baseball Commissioner Bud Selig will be speaking at St. Norbert College next month.',
'Bud Selig to speak at St. Norbert College']

The SentenceTransformers library requires our dataset to be in a specific format. This ensures the data are compatible with the model architecture.

Let’s create a list of the training samples (using half of the dataset for illustrative purposes). This approach reduces the computational load and accelerates the training process.

#convert dataset in required format
train_examples = []
train_data = dataset['train']['set']

n_examples = dataset['train'].num_rows//2 #select half of the dataset for training

for example in train_data[:n_examples]:
    original_sentence = example[0]
    compressed_sentence = example[1]

    input_example = InputExample(texts = [original_sentence, compressed_sentence])

    train_examples.append(input_example)

Now, let’s instantiate the DataLoader class. This class provides an efficient way to iterate over our dataset.

#Instantiate Dataloader with training examples
train_dataloader = DataLoader(train_examples, shuffle = True, batch_size = 16)

Implementation#

In a sentence transformer model, we want to map a variable-length input sentence to a fixed size vector. We start by first passing in the input sentence through a transformer model. In this example, we use the BERT base model (uncased) model as the base transformer model, which outputs the contextualized embeddings for each token in the input sentence. After getting the embeddings for each token, we use the pooling layer to aggregate the embeddings into a single sentence embedding. Lastly, we perform an additional transformation by adding a dense layer (with a Tanh Activation function). This layer reduces the dimensionality of the pooled sentence embeddings while enabling the model to capture more complex patterns in the data by using a non-linear activation function.

# Create a custom model
# Use an existing embedding model
word_embedding_model = models.Transformer('bert-base-uncased', max_seq_length=256)

# Pool function over the token embeddings
pooling_model = models.Pooling(word_embedding_model.get_word_embedding_dimension())

# Dense function
dense_model = models.Dense(in_features=pooling_model.get_sentence_embedding_dimension(), out_features=256, activation_function=nn.Tanh())

# Define the overall model
model = SentenceTransformer(modules=[word_embedding_model, pooling_model, dense_model])

Training#

During training, the selection of an appropriate loss function is crucial and depends on the specific application and the structure of the dataset. For our purposes, we employ the MultipleNegativesRankingLoss function. This function is particularly useful in semantic search applications where the model needs to rank sentences based on their relevance. It operates by contrasting a pair of semantically similar sentences (a positive pair) against multiple dissimilar ones. This function is especially well-suited to our Sentence Compression dataset, as it distinguishes between semantically similar and dissimilar sentences.

#Given the dataset of equivalent sentences, choose MultipleNegativesRankingLoss
train_loss = losses.MultipleNegativesRankingLoss(model = model)
model.fit(train_objectives=[(train_dataloader, train_loss)], epochs = 5)

Inference#

Let’s evaluate the model.

# from sentence_transformers import SentenceTransformer, util
import torch

# Sentences (documents/corpus) to encode
sentences = [
    'Paris, which is a city in Europe with traditions and remarkable food, is the capital of France',
    'The capital of France is Paris',
    'Australia is known for its traditions and remarkable food',
    """
        Despite the heavy rains that lasted for most of the week, the outdoor music festival,
        which featured several renowned international artists, was able to proceed as scheduled,
        much to the delight of fans who had traveled from all over the country
    """,
    """
        Photosynthesis, a process used by plans and other organisms to convert light into
        chemical energy, plays a crucial role in maintaining the balance of oxygen and carbon
        dioxide in the Earth's atmosphere.
    """
]

# Encode the sentences
sentences_embeddings = model.encode(sentences, convert_to_tensor=True)


# Query sentences:
queries = ['Is Paris located in France?', 'Tell me something about Australia',
           'music festival proceeding despite heavy rains',
           'what is the process that some organisms use to transform light into chemical energy?']


# Find the closest sentences of the corpus for each query using cosine similarity
for query in queries:

    # Encode the current query
    query_embedding = model.encode(query, convert_to_tensor=True)

    # Cosine similarity and closest document to query
    cos_scores = util.cos_sim(query_embedding, sentences_embeddings)[0]

    top_results = torch.argsort(cos_scores, descending = True)
    print("\n\n======================\n\n")
    print("Query:", query)
    print("\nSimilar sentences in corpus:")

    for idx in top_results:
        print(sentences[idx], "(Score: {:.4f})".format(cos_scores[idx]))

We demonstrate the efficacy of the model by testing it with a few new examples.

======================


Query: Is Paris located in France?

Similar sentences in corpus:
The capital of France is Paris (Score: 0.7907)
Paris, which is a city in Europe with traditions and remarkable food, is the capital of France (Score: 0.7081)

        Photosynthesis, a process used by plans and other organisms to convert light into
        chemical energy, plays a crucial role in maintaining the balance of oxygen and carbon
        dioxide in the Earth's atmosphere.
     (Score: 0.0657)
Australia is known for its traditions and remarkable food (Score: 0.0162)

        Despite the heavy rains that lasted for most of the week, the outdoor music festival,
        which featured several renowned international artists, was able to proceed as scheduled,
        much to the delight of fans who had traveled from all over the country
     (Score: -0.0934)


======================


Query: Tell me something about Australia

Similar sentences in corpus:
Australia is known for its traditions and remarkable food (Score: 0.6730)
Paris, which is a city in Europe with traditions and remarkable food, is the capital of France (Score: 0.1489)
The capital of France is Paris (Score: 0.1146)

        Despite the heavy rains that lasted for most of the week, the outdoor music festival, 
        which featured several renowned international artists, was able to proceed as scheduled, 
        much to the delight of fans who had traveled from all over the country
     (Score: 0.0694)

        Photosynthesis, a process used by plans and other organisms to convert light into
        chemical energy, plays a crucial role in maintaining the balance of oxygen and carbon
        dioxide in the Earth's atmosphere.
     (Score: -0.0241)


======================


Query: music festival proceeding despite heavy rains

Similar sentences in corpus:

        Despite the heavy rains that lasted for most of the week, the outdoor music festival,
        which featured several renowned international artists, was able to proceed as scheduled,
        much to the delight of fans who had traveled from all over the country
     (Score: 0.7855)
Paris, which is a city in Europe with traditions and remarkable food, is the capital of France (Score: 0.0700)

        Photosynthesis, a process used by plans and other organisms to convert light into
        chemical energy, plays a crucial role in maintaining the balance of oxygen and carbon
        dioxide in the Earth's atmosphere.
     (Score: 0.0351)
The capital of France is Paris (Score: 0.0037)
Australia is known for its traditions and remarkable food (Score: -0.0552)


======================


Query: what is the process that some organisms use to transform light into chemical energy?

Similar sentences in corpus:

        Photosynthesis, a process used by plans and other organisms to convert light into
        chemical energy, plays a crucial role in maintaining the balance of oxygen and carbon
        dioxide in the Earth's atmosphere.
     (Score: 0.6085)

        Despite the heavy rains that lasted for most of the week, the outdoor music festival,
        which featured several renowned international artists, was able to proceed as scheduled,
        much to the delight of fans who had traveled from all over the country
     (Score: 0.1370)
Paris, which is a city in Europe with traditions and remarkable food, is the capital of France (Score: 0.0141)
Australia is known for its traditions and remarkable food (Score: 0.0102)
The capital of France is Paris (Score: -0.0128)

Disclaimers#

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