Although machine learning exists already since decades, the typical data scientist – as you would call it today – would still have to go through a manual labor-intensive process of extracting the data, cleaning, feature extraction, regularization, training, finding the right model, testing, selecting and deploying it. Furthermore, for most machine learning scenarios you do not use one model/algorithms but evaluate a plethora of different algorithms to find one suitable for the given data and and use case. Nowadays a lot of data is available under the so-called Big Data paradigm introducing additional challenges of mastering machine learning on distributed computing platforms.
This blog post investigates on how to ease the burden on the data scientists of manual labor-intensive model evaluation by presenting insights on the recent concept of automated machine learning (AutoML) and if it can be adapted to Big data platforms.
What is AutoML
Machine learning is about learning and making prediction from data. This can be useful in many contexts, such as autonomous robots, smart homes, agriculture or financial markets. Machine Learning – despite the word „machine“ in its name – is mostly a manual process that requires a highly skilled person to execute. Although the learning part is rather automated, this person needs to extract data, transform it in potentially different alternative ways, feed it into many alternative machine learning algorithms as well as using different parameters for the same algorithm, evaluate the quality of the generated prediction model and finally deploy this model for others so that they can make their own predictions without going through this labor-intensive process themselves. This is illustrated in the following figure:
Given this background, it comes at no surprise that huge market places have been created where people sell and buy trained machine learning models. For example, the Azure Machine Learning Market place, the Amazon AWS Artificial Intelligence market place, the Algorithmia Marketplace, the caffe model zoo, deeplearning4j models, mxnet model zoo, tensor flow models or the Acumos Marketplace (based on the open source software).
Nevertheless, most organizations that wants to keep up with the competition in these market places or that do not want to rely on market places due to unique problems in their organizations have still the issue to find skilled persons that create prediction models. Furthermore, machine learning models become so complex that they are not the outcome of a single person, but a team that needs to ensure consistent quality.
Here AutoML comes into play. It can support highly skilled machine learning persons, but also non-skilled machine learning persons to create their own prediction models in a transparent manner. Ideally this is done in an automated fashion for the whole machine learning process, but contemporary technology focuses mostly on the evaluation of different models, a set of suitable parameters for these models („hyperparameter optimization“) and automated selection of the „winning“ (or best) model(s) (this is highlighted in the previous figure in green). In case of several models a ranking is created on a so-called “leaderboard”. This has to be done in a given time budget, ie one has only limited time and resources. Potentially several models could be combined (aka deep learning) in more advanced solutions, but this is currently in its infancy.
Some observations here for this specific focus:
- AutoML does not invent new models. It relies on an exisiting repository of algorithms that it iterates and tries out with different parameters. In itself AutoML can be seen as a “meta-algorithm” over these models.
- Similarly it relies on an existing repository of tests that determine suitability of a model for a given problem.
- It requires clever sampling (size of sample, randomness) of the underlying training data, otherwise it may take very long to evaluate the models or simply the wrong data is used. A preselection of the data by a person is still needed, although the person does not require as much machine-learning specific skills.
- A person still needs to determine for the winning model if it makes sense what it predicts. For this the person does not need machine learning skills, but domain specific skills. For instance, a financial analyst can determine if from a dataset of financial transaction attributes can predict fraud or not.
Big Data platforms
The emergence of the open source Hadoop platform in 2006 introduced Big Data platforms on commodity hardware and networkl clusters to the world. Few years later Hadoop was adopted for data analytics in several data analysis organizations. The main focus of Hadoop was to enable analytic tasks on large dataset in a reliable manner it was not possible before. Meanwhile further improved platforms have been created, such as Apache Flink or Apache Spark, that focus not only on processing large data volumes, but processing them also faster by employing various optimization techniques.
Those platforms employ several nodes that communciate over a network to execute a task in a distributed manner. This imposes some challenges for machine learning, such as:
- Standard machine learning algorithms are not designed to be executed over a distributed network of nodes.
- Not all machine learning algorithms can be converted into a distributed one. For instance, if you need to estimate the parameters of a model then gradient descent might require a lot of memory on a single node. Hence, other estimation methods need to be used to work in parallel on different nodes.
This led to specific machine learning libraries, such as Flink ML or Spark Mlib, for those platforms that supported only a dedicated subset of algorithms that can be executed efficiently and effectively over a given set of nodes communicating via the network.
Tool support for AutoML
AutoML can be very useful for your organization. Amongst others the following tools exist.
|Tool||Description||Supported Models||Supported Hyperparameter optimization|
|Auto-SKLearn||Automated machine-learning toolkit to be used in lieu of the non-automed scikit-learn. Budget can be defined by time and memory as well as search space. Automated preprocessing can be defined. Multicore processing is supported for some of the algorithms.||Multiple classifiers and regressors as well as combinations (ensemble construction)||Bayesian Optimization|
|TPOT||Automated machine-learning toolkit offering various automated preprocessors (e.g. Standard Scaler, Principal Component Analysis).||Multiple classifiers and regressors as well as combinations||Genetic Programing|
|Auto-Weka||Automated machine-learning toolkit. Budget can be defined by time and memory as well as search space.||Multiple classifiers and regressors as well as combinations||Bayesian Optimization|
|Devol||Automated machine-learning toolkit for deep neural network architectures. Expects the data to be prepared and encoded. Sees itself more as support for experienced data scientists.||Neural Networks and combinations.||Genetic Programing|
|Machine.js/Auto-ML||Automated machine learning kit based on auto-ml. Expects the data to be prepared and encoded.||Various classifiers and regressor as well as Neural networks based on the Keras library. Supports combinations.||Genetic Programing / Gridsearch|
Most of these tools support only one method for hyperparameter optimization. However there are several methods. Some models do not require hyperparameter optimization, because they can derive optimal hyperparameter from the trained data. Unfortunately, this is currently integrated in none of the tools.
Those tools might not always be very end user friendly and you still need to deploy them in the whole organization as fat clients instead of light-weight HTML5 browser applications. As an alternative popular cloud provider integrating more assistants in the cloud that help you with your machine learning process.
AutoML on Big Data Platforms
The aforementioned tools have not been primarily designed for Big Data platforms. They usually are based on Python or Java, so one could use them with the Python or Java-bindings of those platforms (cf. Flink or Spark). One could use the available data sources (and efficient data formats such as ORC/Parquet) and sampling functionality of those platforms (e.g. sampling in Flink or sampling in Spark) and feed it into the tools that could even run on the cluster. However, they would only use one node and the rest of the cluster would not be utilized. Furthermore, the generated models are not necessarily compatible with the models provided by the Big Data platforms. Hence, one has to write a manual wrapper around those models so they can be distributed over the cluster. Nevertheless, also these models would only use one node.
This is not necessarily bad, because usually data scientists will not run one dataset to evaluate with AutoML but multiple datasets so you can utilize the whole cluster by running several AutoML processes. However, it also means data size as well as budget for time and memory is limited to one node, which might not be sufficient for all machine learning problems. Another interesting aspect could be to run one or more winning models over a much larger dataset to evaluate it in more detail or to optimize it even more. This would again require a more deep integration of the AutoML tools and Big Data platforms.
H2O AutoML is a recent (March 2018) example on how to provide AutoML on Big Data platforms, but this has currently similar limitations as described before with respect to the Big Data platform. The only advantage currently is that the models can be generated are compatible with the machine learning APIs of the Big Data platforms.
Apache Spark has some methods for hyperparameter tuning, but they are limited to a pipeline or model and do not cover aspects of other AutoML solutions, such as comparing different models. Furthermore, it only evaluates out a list of given sets of parameters and no time or cost budget definition is possible. This would have to be implemented by the user.
One can see that AutoML and Big Data platforms can benefit from a more tighter integration in the future. It would then also be more easy to leverage all the data in your data lake without extracting it and process it locally. At the moment, although some machine learning models are supported by Big Data platforms (with some caveats related to distributed processing) not all functionality of AutoML is supported (e.g. hyperparameter tuning or genetic programing).
Google AutoML provides an automated machine learning solution in the cloud. It augments it with pre-trained models (e.g. on image data), so not everyone has to spend time again to train models.
AutoML is a promising tool to facilitate the work of less skilled and very skilled machine learning persons to enable them to have more time focusing on their work instead of the manual error-prone labour-intensive machine learning process. You can make your organisation on-board on machine-learning even if you are in your early machine learning stages and facilitate learning of many people on this topic.
However, it does not mean that people without knowledge can use it out of the box. They should have a least a basic knowledge on how machine learning works in general. Furthermore, they should be domain experts in your organizations domain, e.g. a financial analyst in banks or an engineer in the car industry. They still need to decide which data to input to AutoML and if the model learned by AutoML is useful for your business purposes. For example, it does not make sense to put all the data of the world related to problematic situations for autonomous cars into an AutoML and expect that it can solve all problematic situation as best as possible. Moreover, it is more likely to be country/region-specific so it may make more sense to have several AutoML runs with different countries/regions to develop specific models for countries/regions. Other datasets, such as blockchains/cryptoledgers are more complex and require currently a manual preprocessing and selection.
Another example is known from spurious correlations, ie correlations that exists, but do not imply causality. In all this case you still need a domain expert that can judge if the model is a useful contribution for the organization.
All these things are related to the no free lunch theorem.
Even for highly-skilled machine learning persons AutoML can make sense. No-one can know all particularities of machine learning models and it simply takes a lot of time to evaluate them all manually. Some may even have their favorite models, which may mean other models are not evaluated although they may fit better. Or they simply do not have time for manual evaluation, so a preselection of candidate models can also be very useful.
One open issue is still how much time and resources you should let AutoML spend on a specific dataset. This is not easy to answer and here you may still need to experiment if the results are bad then you need to spend probably more.
Nevertheless, AutoML as a recent field still has a lot of room for improvements, such as full integration in Big Data machine learning platforms or support of more hyperparameter tuning algorithms as well as more user-friendly use interfaces, as pioneered by some cloud services.
Then, those models should be part of a continuous delivery pipeline. This requires unit testing and integration testing to avoid that the model has obvious errors (e.g. always returns 0) or that it does not fit into the environment in which it is used for prediction (e.g. web service cannot be called or model cannot be opened in R). Integration machine learning models into continuous delivery pipelines for productive use has not recently drawn much attention, because usually the data scientists push them directly into the production environment with all the drawbacks this approach may have, such as no proper unit and integration testing.