Technical Tests of a Data Vault Powered EDW

Introduction

In this newsletter, we’ll discuss and make an overview of different methods and approaches when performing technical tests of a Data Vault-powered EDW.
The testing approaches described below are aimed to ensure the integrity, reliability, accuracy, consistency, and auditability of the data loaded into your Data Vault entities as well as the information marts built on top of them. All to ensure that it is safe for your business to make decisions based on that data.

In a webinar session dived deeper into this topic with the main focus on testing the Data Vault entities in the Raw Vault and Business Vault layers. Watch the recording here for free!

What to expect

You will receive an overview of testing approaches suitable for different layers of your EDW solution starting from extracting data from sources to the landing zone/staging area (Extract and Load) and ending with information marts used by end users in their BI reports. Additionally, we will discuss test automation and its importance for continuous integration of your Data Vault-based EDW. That stated, the main focus of this newsletter though is testing the Data Vault entities in the Raw Vault and Business Vault layers.

Testing Data Extraction Process

Regardless of where the data extraction takes place – data source, persistent staging, transient staging – the main goal of testing at this phase is to prove that there is no leakage while transporting or staging the data. Comparing the input data and the target data ensures that the data has not been accidentally or maliciously erased, added, or modified due to any issues in the extraction process.
Checksums, hash totals, and record counts shall be used to ensure the data has not been modified:

• Ensure that checksums over the source dataset and the target staging table are equal
• Ensure that the numerical sum of one or more fields in a source dataset (aka hash total) matches the sum of the respective columns in the target table. Such sum may include data not normally used in calculations (e.g., numeric ID values, account numbers, etc.)
• Make sure the row count between the source and the target staging table matches

Testing Data Vault

The core part of your Data Vault-powered EDW solution is a Raw Data Vault which contains raw and unfiltered data from your source systems that has been broken apart and loaded into hubs, links, satellites, and other Data Vault-specific entities based on business keys. This is the first point in the data pipeline in which the data lands in the Data Vault-modeled entities . Thus, specific tests are required to ensure consistency and auditability of the data after the Raw Data Vault is populated. The below test approaches are valid for Business Vault entities as well.

Testing Hubs

Hubs store business keys by separating them from the rest of the model. A hub is created for every business object. It contains a unique list of keys representing a business object that have the same semantic meaning and granularity. The business objects residing in a hub are then referenced from other Data Vault entities through hash keys calculated during the staging phase.

As such, the following tests are necessary to perform on hubs to ensure their consistency:
For a hub with a single business key, tests should ensure that:

• A hub contains a unique list of business keys (primary key (PK) test)
• A business key column contains no NULL or empty values (except when business key is composite)

If a hub has a composite business key, ensure that:

• The combination of the values in the business key columns are unique (PK test)
• Business key columns don’t contain NULL or empty values all at once

The validity of the latter point also depends on the nature of the business objects itself. It can also be that NULLs or empty values are not allowed in any of the business key columns.

For the both kinds of hubs, ensure that:

• Hash key column contains:
  • Unique list of values (PK test)
  • No NULLs or empty values

Testing Links

A typical link defines relationships between business objects by storing unique combinations of hash keys of the connected hubs. The primary key of the link or link hash key uniquely identifies such a combination. Thus, link tests should check that:

• The combination of connected hub references (hub hash keys) is unique (PK test)
• Every hub hash key value exists in the referenced hub
• Hub references do not contain NULLs or empty values

Regarding the last bullet point, note that the NULLs and empty values in hub references, as well as in hash key columns of other Data Vault entities, are replaced with zero keys.
For transactional (non-historized) data, transactional key columns should be included into the uniqueness tests in addition to columns with hub hash keys. Make sure that transactional keys are populated as well. Such transactional keys are usually not hashed since, as a rule, no hubs for transactions are created.
And, as for hubs, make sure that the link hash key column contains unique values and there are no NULLs and empty values.

Testing Satellites

Satellites store descriptive information (attributes) for business objects (residing in hubs) or relationships between business objects (residing in links). One satellite references either one hub or one link. Since descriptive information for business objects and relationships between them may change over time, a load date timestamp of a satellite record is added to the primary key of a satellite.

With the above said, tests for a satellite should make sure that:

• The combination of a hub/link reference (the Hash Key) and the load date timestamp of a record is unique (PK test)
• Every hub or link hash key value exists in the referenced hub or link
• Hub or link references do not contain NULL or empty values

Multi-active satellites contain multiple active records at the same time. Thus, additional key columns (for example, Type Code, Sequence, etc.) are needed to uniquely identify a record. These additional key columns have to be part of the unique test of a multi-active satellite. Additionally, they should be tested for the absence of NULL and empty values.
The approach for testing a non-historized satellite also differs a bit from testing its standard sibling. A non-historized satellite is a special entity type that contains descriptive attributes for every corresponding record in a non-historized link. A primary key of a non-historized satellite is a link hash key. Thus, there is no need to include a load date timestamp into the primary key check. For a non-historized satellite, additionally make sure that it has a 1:1 relationship with the corresponding non-historized link. Record counts in both entities should match exactly.

Testing Other Data Vault Entities

There are other special entity types in Data Vault worth mentioning in regards to testing:

• Reference hubs and reference satellites: Testing approaches are similar to standard hubs and satellites. The only difference is there are no hash keys and business keys are used directly.
• Record source tracking satellites: A column representing a static source name is added to the primary key test.
• PIT Table (Business Vault):
  • PK test – combination of the hub/link hash key and the snapshot date timestamp columns is unique
  • For every satellite reference, check that the pair of hub/link hash keys and the load date timestamp exists in the referenced satellite
  • Hub/link reference does not contain NULL or empty values
• Bridge Table (Business Vault):
  • PK test – combination of a base link hash key and snapshot date timestamp columns is unique
  • For every hub and link reference, check that a pair of hub/link hash key exists in the referenced hub or link

General Tests for all Data Vault Entities

There are some tests applicable for all Dava Vault entities.
Make sure that all Data Vault entities:

• Contain zero keys instead of NULL keys
• Have records source columns that are populated and correspond to the defined pattern (e.g., regex). For example, check if it contains the file path where the name of the top level folder represents the name of the source system and the file name includes the timestamp of the data extraction
• Don’t have NULL values in their load (snapshot) date timestamp columns

Testing Source Marts

The Source Mart is one of the facets of the Information Mart concept in the Data Vault. It is a virtualized model on top of the Raw Data Vault with the aim of replicating the original source structures. It is great for ad-hoc reporting and offers higher value for many data scientists and power users and can also be used to test consistency and auditability of the loading process into a Data Vault-powered EDW.

Source mart objects are intended to look the same as the respective source tables (including columns names). If you have source marts implemented in your EDW, make sure to compare them against the respective source tables in the staging area after the data loading process. Values and row counts of source structures should match exactly against the respective source mart objects. In the Data Vault community, this kind of test is also known as a “Jedi-Test”.

It is relatively easy to automate such comparison and make it a part of the loading process.

Testing Hash Key and Hash Diff Calculations

Hash keys in Data Vault allows business keys to be integrated in a deterministic way from multiple sources in parallel. They are the glue that binds different Data Vault entities together.

Hash diffs, on the other hand, apply to the satellites and help identify differences in descriptive attributes during the data loading process.

It is important to introduce unit tests for hash key and hash diff calculations used in your EDW, to make sure the hashed values are calculated in accordance with the hashing standards defined. Read more about requirements and templates for hashing here. Test cases for such unit tests should cover as many combinations of different data types and values (e.g. NULL and empty values) as possible, to ensure that they are calculated consistently.

In case your EDW exists on different DBMS platforms (e.g. during migration process or data security regulations), the above test cases can be used to make sure that your hash calculations are platform agnostic, meaning that they produce the same result on different platforms. There is a common use case, when a link in an on-premise DBMS platform references a hub that was already migrated to a Cloud platform. Such unit tests can be run on both platforms to ensure consistency of hashing during a migration.

Testing Business Rules

Unlike the hard rules that do not alter or interrupt the contents of the data, maintaining auditability, soft or business rules enforce the business requirements that are stated by the business users. Examples of business rules can include:

• Concatenation (last name and first name)
• Standardizing phone numbers
• Computing total sales (aggregation)
• Coalescing, etc.

Apart from the relatively simple examples listed above, there might also be some more complex business rules involving sophisticated calculations, data transformations, and complex joins. Depending on the use case, the results of applying such rules usually end up in the Business Vault (i.e. a Business Satellite) and later in the Information Mart layer where they are consumed by the business users. Thus, testing business rules is an important part of the information delivery process.

Business rules are usually also a subject of unit testing that must be done continuously during the development and CI process. To perform such a unit test, we need some expected values, in the best case provided by the business, i.e., an expected net sales value for a defined product or a set of products in a specific shop on a named day based on the real data. The net sales calculation from our Business Vault is then tested against the given expected result.

Test Automation and Continuous Integration

All of the above described tests should be automated as much as possible and run by EDW developers during the development process. Successful tests should be an obligatory condition for introducing any new change to your EDW code base. That is achievable by using DevOps tools and enabling continuous integration (CI) in your DWH development lifecycle. Running automated tests each time code is checked or merged ensures that any data consistency issues or bugs are detected early and fixed before they are put into production. As a rule, a separate test (or CI) environment is created for the purpose of running automated tests.

Here are some general recommendations for creating and running a test environment:

• Create the CI environment as similar as possible to the production environment
• Create test source databases and source files derived from real data
• The test source files and source databases should be small so tests can run quickly
• The test source files and source databases should also be static so that the expected results are known in advance
• Test full load and incremental load patterns since the logic of both patterns is different in most of the cases
• Run tests not only against the changes to be merged but also against all the downstream dependencies, or even the whole loading process in general to prevent regressions.

Conclusion

In this newsletter, we provided an overview of different methods and approaches for the process of technical testing a Data Vault powered EDW.

We covered testing of different stages of the EDW load including extraction of the data from data sources, loading Data Vault entities, and information delivery process, though primary focus was placed upon loading Data Vault entities.

We also covered unit testing hash key & hash diff calculations.

It is important to make sure that your hashing solution is platform/tool agnostic, especially during the migration process.

We also learned that testing business rules is a key part of the information delivery process since they interpret the data and define what business users see in their reports. We highlighted the importance of unit testing the business rules and cooperation with the business in respect to defining test cases and expected results.

Furthermore, we also stressed the significance of test automation during the development phase as well as for enabling continuous integration and provided recommendations for creating and running a test environment.

We go even deeper into this topic in our webinar. Make sure to watch the recording for free!

– Dmytro Polishchuk (Scalefree)

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