The first swimlane in Fig. 1 illustrates the Pipelining work stream. In this stream, the data engineer prepares the data sets for ML modeling, training, and inference. The activities are summarized in the following table.

Activity Description Inputs Outputs
Acquire Data The necessary raw data from the data sources (e.g., databases, edge devices) are aggregated for ML modeling, training, and inference. Various data sources Raw data
Clean Data The raw data are cleaned so that the data quality is sufficient for labeling or preprocessing. Raw data Cleaned data
Label Data Data points are labeled with expected inference outputs. Manual labeling may be necessary. Cleaned data Labeled data
Preprocess Inference Inputs The data are transformed to the specific format required for input to the inference application Cleaned data Inference inputs
Preprocess Training Data The data sets are transformed to the specific file format required by the ML library for training. Labeled data Training data
Validate Inference Outputs The actual inference outputs are compared against the expected outputs, which can be a manual process. Inaccurate outputs can be selected for relabeling to continously train and improve the ML model in the future. Actual inference outputs Selected outputs for relabeling

Acquire Data

In this activity, the necessary raw data sets are acquired for ML modeling, training, and inference. Data integration may be involved in generating ML data points that cover data fields from multiple data sources. Traditional Extract, Transform, Load (ETL) tools and Enterprise Service Bus (ESB) may be used for simplifying data acquisition and integration. Raw data often come in a variety of forms and thus are commonly stored in data files or a database with a schemaless or columnar structure.

Clean Data

In this activity, the quality of the data sets is improved up to the standard required for the downstream ML. Through data cleansing, the raw data are cleaned so that the resultant data for ML are as valid, accurate, complete, consistent, and uniform as expected. The data may go through a series of multiple data cleansing procedures, such as value validition, data reformatting, duplicate elimination, and statistical analysis. Since the inference data do not have labels, cleaned data are often directly be used for inference preprocessing.

Label Data

In this activity, the data are labeled to support the supervised ML. (For unsupervised ML, this step may be skipped.) The labeling process often involves manual labeling but can also be automated in some use cases. This aims to map each data point to the expected inference outputs. An output can be a set of labels (for classification) or values (for regression). A data scientist can use the labeled data set to experiment different ML models and tune the hyperparameters during ML design. After the ML model is designed and programmed, the labeld data set is used to train the model in the Training work stream.

Preprocess Inference Inputs

In this activity, the cleaned and / or labeled data are transformed to the input format required by the inference application to process in the Inference work stream, for example, in form of API requests, a message stream, or a data file. How the inference input data should be constructed and submitted depends on the specific input requirements of the inference application.

Preprocess Training Data

In this activity, the training data sets are produced for modeling Modeling work stream or training in the Training work stream. The file format can be specific to the ML library used. The training data can be split into two sets: training set and testing set. The training set is used to train the model while the testing set is used to validate the model for its accuracy.

Validate Inference Outputs

The outputs from the inference application in the Inference work stream are fed back for validation against the expected results. The outputs, especially those which are insufficiently accurate, can be relabeled (manually) can be merged into the new training and testing sets for retraining in the Training work stream so as to continously improve the model.