Key Concepts of Convolutional Neural Networks

Srinija Sirobhushanam takes us through some of the key concepts around convolutional neural networks:

How are convolution layer operations useful?
CNN helps us look for specific localized image features like the edges in the image that we can use later in the network Initial layers to detect simple patterns, such as horizontal and vertical edges in an image; and deeper layers detect complex patterns.

This is a rather high-level description of the topic, but it serves to give an understanding of what you need to know before building and using these networks.

LSTM in Databricks

Vedant Jain shows us an example of solving a multivariate time series forecasting problem using LSTM networks:

LSTM is a type of Recurrent Neural Network (RNN) that allows the network to retain long-term dependencies at a given time from many timesteps before. RNNs were designed to that effect using a simple feedback approach for neurons where the output sequence of data serves as one of the inputs. However, long term dependencies can make the network untrainable due to the vanishing gradient problem. LSTM is designed precisely to solve that problem.

Sometimes accurate time series predictions depend on a combination of both bits of old and recent data. We have to efficiently learn even what to pay attention to, accepting that there may be a long history of data to learn from. LSTMs combine simple DNN architectures with clever mechanisms to learn what parts of history to ‘remember’ and what to ‘forget’ over long periods. The ability of LSTM to learn patterns in data over long sequences makes them suitable for time series forecasting.

This is a nice overview and as a bonus, there’s a notebook as well where you can try it on your own.

Performance Tuning Neural Network Training

Sean Owen takes us through a few techniques for speeding up neural network model training:

Step #2: Use Early Stopping
Keras (and other frameworks) have built-in support for stopping when further training appears to be making the model worse. In Keras, it’s the EarlyStopping callback. Using it means passing the validation data to the training process for evaluation on every epoch. Training will stop after several epochs have passed with no improvement. restore_best_weights=True ensures that the final model’s weights are from its best epoch, not just the last one. This should be your default.

Sean focuses here on Keras + TensorFlow on Spark, but several of the tips are cross-product and generally applicable.

Text Analysis from Google Sheets

Federico Pascual shows how you can use MonkeyLearn to perform text analysis (including sentiment analysis and categorization) from a Google Sheets spreadsheet:

Carrying out a customer survey, for example, can be useful to obtain crucial insights into the overall customer experience of your clients. But the data obtained from these surveys can be incredibly difficult to process, even after you’ve added all the results to a spreadsheet and especially if you receive a high volume of responses. 

How do you process this information, then? Should you read the answers one by one? What if you want to know what people are saying about your brand on social media?

Click through for a demo.

SQL Server CTP 3.2 and Java Extensibility

Niels Berglund walks us through what has changed with Java support in ML Services in SQL Server 2019 CTP 3.2:

One of the announcements of what is new in CTP 3.2 was that SQL Server now includes Azul System’sZulu Embedded right out of the box for all scenarios where we use Java in SQL Server, including Java extensibility.

So, in this post, we look at the impact, (if any), this has to how we use the Java extensibility framework in SQL Server 2019.

This also affects PolyBase.

MLflow 1.1 Released

Max Allen, et al, announce the release of MLflow 1.1:

We’re excited to announce today the release of MLflow 1.1. In this release, we’ve focused on fleshing out the tracking component of MLflow and improving visualization components in the UI.

Some of the major features include:
– Automatic logging from TensorFlow and Keras
– Parallel coordinate plots in the tracking UI
Pandas DataFrame based search API
– Java Fluent API
– Kubernetes execution backend for MLflow projects
– Search Pagination

Looks like they’re putting in a lot of work on this.

Building an Image Classifier with PyTorch

Rogier van der Geer shows how you can use PyTorch to build out a Convolutional Neural Network for image classification:

The tool that we are going to use to make a classifier is called a convolutional neural network, or CNN. You can find a great explanation of what these are right here on wikipedia.

But we are not going to fully train one ourselves: that would take way more time than I would be willing to spend. Instead, we are going to do transfer learning, where we take a pre-trained CNN and replace only the last layer by a layer of our own. Then we only need to train that single layer, as all the other layers already have weights that are quite sensible. Here we exploit the fact that the images we are interested in have a lot of the same properties as those images that the original network was trained on. You can find a great explanation of transfer learning here.

Read on for a detailed example.

xgboost and Small Numbers of Subtrees

John Mount covers an interesting issue you can run into when using xgboost:

While reading Dr. Nina Zumel’s excellent note on bias in common ensemble methods, I ran the examples to see the effects she described (and I think it is very important that she is establishing the issue, prior to discussing mitigation).
In doing that I ran into one more avoidable but strange issue in using xgboost: when run for a small number of rounds it at first appears that xgboost doesn’t get the unconditional average or grand average right (let alone the conditional averages Nina was working with)!

It’s not something you’ll hit very often, but if you’re trying xgboost against a small enough data set with few enough rounds, it is something to keep in mind.

A Quick Keras Example

Shubham Dangare takes us through a quick example using Keras and TensorFlow in Python:

Keras is a high-level neural networks API, written in Python and capable of running on top of Tensorflow, CNTK  or Theano. It was developed with a focus on enabling fast experimentation. In this blog, we are going to cover one small case study for fashion mnist.

Fashion-MNIST is a dataset of Zalando’s article images—consisting of a training set of 60,000 examples and a test set of 10,000 examples. Each example is a 28×28 grayscale image, associated with a label from 10 classes. Zalando intends Fashion-MNIST to serve as a direct drop-in replacement for the original MNIST dataset for benchmarking machine learning algorithms. It shares the same image size and structure of training and testing splits.

The end result wasn’t that great, but Shubham was using a sequential model rather than a convolutional neural network, so you can probably take this as a starting point and improve upon it.

ML Services and Injectable Code

Grant Fritchey looks at sp_execute_external_script for potential SQL injection vulnerabilities:

The sharp eyed will see that the data set is defined by SQL. So, does that suffer from injection attacks? Short answer is no. If there was more than one result set within the Python code, it’s going to error out. So you’re protected there.

This is important, because the data set query can be defined with parameters. You can pass values to those parameters, heck, you’re likely to pass values to those parameters, from the external query or procedure. So, is that an attack vector?

No.

Another factor is that you need explicitly to grant EXECUTE ANY EXTERNAL SCRIPT rights to non-sysadmin, non-db_owner users, meaning a non-privileged user can’t execute external scripts at all. You can also limit the executing service account

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