is not allowing an order total to be greater than the credit limit assigned to a customer.
The decision to keep the row or delete it will depend on the particular use case. A set of telemetry data arriving at one-minute intervals may include an invalid value. In that case, the invalid value may be dropped without significantly affecting hour-level aggregates. A customer order that violates a business rule, however, might be kept because orders are significant business events. In this case, the order should be processed by an exception-handling process.
Transformations also include normalizing or standardizing data. For example, an application may expect phone numbers in North America to include a three-digit area code. If a phone number is missing an area code, the area code can be looked up based on the associated address. In another case, an application may expect country names specified using the International Organization for Standardization (ISO) 3166 alpha-3 country code, in which case data specifying Canada would be changed to CAN.
Cloud Dataflow is well suited to transforming both stream and batch data. Once data has been transformed, it is available for analysis.
Data Analysis
In the analyze stage, a variety of techniques may be used to extract useful information from data. Statistical techniques are often used with numeric data to do the following:
Describe characteristics of a dataset, such as a mean and standard deviation of the dataset.
Generate histograms to understand the distribution of values of an attribute.
Find correlations between variables, such as customer type and average revenue per sales order.
Make predictions using regression models, which allow you to estimate one attribute based on the value of another. In statistical terms, regression models generate predictions of a dependent variable based on the value of an independent variable.
Cluster subsets of a dataset into groups of similar entities. For example, a retail sales dataset may yield groups of customers who purchase similar types of products and spend similar amounts over time.
Text data can be analyzed as well using a variety of techniques. A simple example is counting the occurrences of each word in a text. A more complex example is extracting entities, such as names of persons, businesses, and locations, from a document.
Cloud Dataflow, Cloud Dataproc, BigQuery, and Cloud ML Engine are all useful for data analysis.
Explore and Visualize
Often when working with new datasets, you’ll find it helpful to explore the data and test a hypothesis. Cloud Datalab, which is based on Jupyter Notebooks (http://jupyter.org), is a GCP tool for exploring, analyzing, and visualizing data sets. Widely used data science and machine learning libraries, such as pandas, scikit-learn, and TensorFlow, can be used with Datalab. Analysts use Python or SQL to explore data in Cloud Datalab.
Google Data Studio is useful if you want tabular reports and basic charts. The drag-and-drop interface allows nonprogrammers to explore datasets without having to write code.
As you prepare for the Google Cloud Professional Data Engineer exam, keep in mind the four stages of the data lifecycle—ingestion, storage, process and analyze, and explore and visualize. They provide an organizing framework for understanding the broad context of data engineering and machine learning.
Technical Aspects of Data: Volume, Velocity, Variation, Access, and Security
GCP has a wide variety of data storage services. They are each designed to meet some use cases, but certainly not all of them. Earlier in the chapter, we considered data storage from a business perspective, and in this section, we will look into the more technical aspects of data storage. Some of the characteristics that you should keep in mind when choosing a storage technology are as follows:
The volume and velocity of data
Variation in structure
Data access patterns
Security requirements
Knowing one of these characteristics will not likely determine the single storage technology you should use. However, a single mismatch between the data requirements and a storage service’s features can be enough to eliminate that service from consideration.
Volume
Some storage services are designed to store large volumes of data, including petabyte scales, whereas others are limited to smaller volumes.
Cloud Storage is an example of the former. An individual item in Cloud Storage can be up to 5 TB, and there is no limit to the number of read or write operations. Cloud Bigtable, which is used for telemetry data and large-volume analytic applications, can store up to 8 TB per node when using hard disk drives, and it can store up to 2.5 TB per node when using SSDs. Each Bigtable instance can have up to 1,000 tables. BigQuery, the managed data warehouse and analytics database, has no limit on the number of tables in a dataset, and it may have up to 4,000 partitions per table. Persistent disks, which can be attached to Compute Engine instances, can store up to 64 TB.
Single MySQL First Generation instances are limited to storing 500 GB of data. Second Generation instances of MySQL, PostgreSQL, and SQL Server can store up to 30 TB per instance. In general, Cloud SQL is a good choice for applications that need a relational database and that serve requests in a single region.
Velocity
Velocity of data is the rate at which it is sent to and processed by an application. Web applications and mobile apps that collect and store human-entered data are typically low velocity, at least when measured by individual user. Machine-generated data, such IoT and time-series data, can be high velocity, especially when many different devices are generating data at short intervals of time. Here are some examples of various rates for low to high velocity:
Nightly uploads of data to a data
Hourly summaries of the number of orders taken in the last hour
Analysis of the last three minutes of telemetry data
Alerting based on a log message as soon as it is received is an example of real-time processing
If data is ingested and written to storage, it is important to match the velocity of incoming data with the rate at which the data store can write data. For example, Bigtable is designed for high-velocity data and can write up to 10,000 rows per second using a 10-node cluster with SSDs. When high-velocity data is processed as it is ingested, it is a good practice to write the data to a Cloud Pub/Sub topic. The processing application can then use a pull subscription to read the data at a rate that it can sustain. Cloud Pub/Sub is a scalable,
