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Building a Single Customer View Using Open-Source Tools and Databricks

A scalable data quality and record linkage workflow enabling customer data science


A single customer view is a comprehensive representation of a customer’s data across all interactions with a business. It combines data from multiple sources, such as purchases, interactions with websites, social media, email enquiries, feedback, and any other data sources, into a single record per unique customer [1]. Once achieved a single customer view offers many opportunities for targeted marketing, improved customer retention and maximising customer lifetime value [2]. However, arriving at a single customer view and maintaining it over time can be challenging, with data quality limitations, the cost of licensing many third-party master data management (MDM) tools and customer privacy and compliance considerations for the handling of personal data, all complicating the construction of a single customer view. This article offers an approach to building a data quality and record linkage pipeline for single customer views, taking into account these challenges and offering a low-cost open-source approach using the Spark-based cloud computing platform Databricks.

Solution Overview

The diagram below summarises an open-source approach to generating a single customer view using Databricks. In a series of Databricks notebooks connected in a workflow, we can implement data profiling and validation checks with the help of the Great Expectations library, address any data quality issues and ensure compliance with data protection and retention policies in a cleansing and compliance notebook, use the Splink library for probabilistic record linkage between or within customer data tables and finally apply golden record logic and join all customer records, to deduplicate and link disparate customer datasets, generating the single customer view.

Overview of an open-source data quality and record linkage workflow in Databricks. Image by author

All transformations are implemented in queries written in Pyspark/Spark SQL or utilising the Spark backends of any open-source components, so that we leverage the parallel computing power of Databricks to scale the processing required in the various stages to potentially accommodate massive customer datasets. Using a Lakehouse architecture for the storage of all intermediate tables and finished outputs we can benefit from an audit log of all operations performed on the data, delete customer data permanently if required for compliance, whilst retaining anonymised information for analytics purposes and benefit from the performance and reliability of the Delta table format [3]. Data enters the process from source systems (e.g., customer relationship management (CRM) tools such as Dynamics 365 or Salesforce) and leaves in the form of a single customer view ready for analytical or operational use cases, such as customer profiling dashboards, machine learning applications such as recommendation engines and automated marketing and upselling via email, text or post.

Profiling and Validation Using Great Expectations

Great Expectations is an open-source Python library [4] that allows you to programmatically create automated tests for data pipelines, ensuring that the data is valid, complete, and of consistent schema. Users can define dictionaries of expectations, for fields in their data, and then test their data against those expectations.

# contactid
expectation_type = “expect_column_values_to_not_be_null”,
kwargs = {‘column’:’contactid’},
meta = {‘reason’:’contactid is the unique ID for D365 contacts,
this should not be null’})

Example of an expectation definition using great expectations

The library provides a wide range of expectations out of the box, such as testing for null values, unique values and value ranges; users can also create custom expectations if the standard set doesn’t provide the expectation required for their dataset. Great Expectations supports a variety of data sources, including databases, CSV files, and Pandas or Pyspark dataframes and can take advantage of the Spark backend when using Databricks. After running a validation test, the user is provided with a web-based data validation report, which highlights which fields have passed and which fields have not passed the expectation suite and if so why not, as shown in the example below.

Data validation report produced with Great Expectations https://docs.greatexpectations.io/docs/

Great Expectations also offers data profiling, allowing the user to gain insights into their datasets, such as summary statistics (mean, median, and standard deviation), completeness and uniqueness and provides a suite of visualisation tools to enable users to explore their data and identify potential issues. These insights may highlight the need for additional expectations in the suite or alerts to be sent to data stewards, if subsequent iterations of customer data move outside of their expected values.

In the context of building a single customer view, Great Expectations can help you understand the composition and quality of customer datasets and verify outputs before they are passed to subsequent steps in the pipeline or handed over to downstream applications. Great Expectations can be used to initially highlight data quality issues during the first pass over customer datasets and in production can be integrated with CI/CD tools to enable the unit testing of datasets as part of a deployment pipeline.

Cleansing and Compliance

The cleansing and compliance stage involves addressing any data quality issues highlighted by profiling and validation and ensuring that stored customer data is compliant with any restrictions on data retention (e.g. GDPR [5]). In Databricks this can be achieved using Pyspark/Spark SQL queries, selecting, filtering, or mapping fields or values to provide the desired set of data cleansing operations.

Customer datasets contain personally identifiable information (names, email addresses, phone numbers and postal addresses) which are crucial for the linkage of customer data from multiple sources. Each customer dataset will also have attributes associated with each customer, such as transaction logs, preferences, flags indicating memberships/statuses and timestamps indicating when communications were made with them. In order to prepare data for a single customer view, these datasets may need to be aggregated so that any time series or event log datasets are summarised into single row per entity tables that can subsequently be joined and/or deduplicated/linked in the probabilistic matching stage.

Data retention policies may also be implemented programmatically at this stage as well as code for specific user deletion requests. Delta Lake offers optimisations that make point deletes in data lakes more efficient using data skipping [6]. If personally identifiable information is not necessary for downstream uses of the customer data, it can be permanently anonymised at this stage or pseudonymised/split into sensitive and non-senstitve tables with different levels of permissions so that access to the raw customer data is restricted [3].

DELETE FROM data WHERE email = ‘cu******@ex***********.com’;
VACUUM data;

Example of a point delete of a customers’ data in a Delta table

Probabilistic Record Matching Using Splink

Customer datasets often contain duplicates of each unique customer; customers may manually input their details introducing spelling errors, over time customers might move address or change account information creating multiple records with only one being valid and up-to-date and where the customer is represented in multiple datasets there will obviously be multiple records between those tables which require linkage. This problem of deduplication and record linkage can be addressed using Splink [7], an open-source probabilistic record matching algorithm implemented in Spark, created by a team at the UK Ministry of Justice to assist record matching for judicial applications.

Example of a customer dataset in need of deduplication and linkage https://github.com/moj-analytical-services/splink

Splink uses a Bayesian algorithm to combine fuzzy matching scores across multiple fields into an overall match probability, enabling the user to mark customer records as linked between tables or as duplicates of a given individual within tables, using those match probability thresholds. The user can define a suite of fuzzy matching scores to be calculated such as Jaccard similarity and Levenshstein distance over various personal data fields, such as names, emails, phone numbers and addresses, as well as blocking rules which reduce the computational complexity of the matching process, by limiting fuzzy matching comparisons to records with exact matches on other fields. A probabilistic record linkage model is trained using expectation maximisation and used to generate match probabilities for each pairwise comparison included in the prediction blocking rules. The output of this prediction stage represents a graph data structure, with all pairwise comparisons of records as nodes connected with edges representing their pairwise match probabilities and this graph can be resolved into clusters of highly connected similar records with match probabilities greater than a user-defined threshold, using the connected components algorithm.

Overview of a typical Splink deduplication workflow. https://github.com/moj-analytical-services/splink edited with permission by the author.

Although Splink requires numerous decisions from the user in order to carry out linkage successfully, most notably choosing the confidence level at which to accept or reject matches across the range of match probabilities generated, being an open-source project Splink does not require the licensing fees required for commercial record matching tools and works well provided suitable matching rules and blocking rules are chosen and match probability thresholds are set appropriately. To evaluate the quality of the linkage provided by Splink, a data steward should ideally manually verify the match quality of a random sample of matched records to build confidence in the output and potentially trade-off false positive and false negative rates, depending on the criticality of the final application of the data.

Evaluation of match accuracy by inspection of a random sample of pairwise matches at different match probabilities. https://github.com/moj-analytical-services/splink edited with permission by the author.

Golden Record Logic

Once duplicate records or linked records between tables are identified, the final stage in building a single customer view is to implement golden record logic, to unify all records per unique customer into a single row with a defined set of fields containing all relevant customer data for downstream use [8]. The decision as to which fields and which copies of a customer’s information to carry forward as golden records, will be determined by how the data will be used, knowledge of recording practices and criteria for relevance. In the example below, a custom golden record logic is applied in Pyspark over a customer dataset deduplicated in Splink (where unique customers have been assigned a unique “cluster_id”), selecting the most recent and most complete duplicate records for a customer. Other applications may see multiple records and fields, from potentially multiple tables, combined to make a composite record. Moreover, multiple golden record definitions might also be applied over the same data and used for different purposes (e.g., customers with memberships may have a different set of golden record logic applied to them compared to non-members). Often a given marketing use case will require a particular subset of the customer data and multiple marketing use cases may be derived from the same dataset; for each of these marketing use cases, a different set of flags can be implemented at this stage, to make their selection convenient downstream.

# count nulls
df_nulls_counted = df.withColumn(‘numNulls’, sum(df[col].isNull().cast(‘int’) for col in df.columns)*-1)

# flag most complete
df_most_complete = df_nulls_counted.withColumn(“row_number”,f.row_number()
.withColumn(‘most_complete’, f.when(f.col(“row_number”)==1, 1).otherwise(0)).drop(“row_number”)

# flag most recent
df_most_complete_most_recent = df_most_complete.withColumn(“row_number”,f.row_number()
.withColumn(‘most_recent’, f.when(f.col(“row_number”)==1, 1).otherwise(0)).drop(“row_number”)

# order by number of nulls
df_golden = df_most_complete_most_recent.withColumn(“row_number”,f.row_number()
.orderBy(*[f.desc(c) for c in [“numNulls”,”createdon_timestamp”]]))).cache()
.withColumn(‘golden_record’, f.when(f.col(“row_number”)==1, 1).otherwise(0)).drop(“row_number”)

# add splink duplicate flag
df_golden = df_golden.select(‘*’, f.count(‘cluster_id’)
.withColumn(‘splink_duplicate’, f.when(f.col(‘dupeCount’) > 1, 1).otherwise(0))

Example golden record logic implemented using Pyspark window functions and binary flags

Integrations and Use Cases

An Azure architecture such as the one shown below can be used for the cloud deployment of the single customer view, as a platform for customer analytics and data science use cases [9]. Using a cloud platform such as Azure, allows you to scale in a cost-effective way and also simplify the data protection and compliance aspects associated with storing and using customer data. Azure also offers a suite of ETL and data science components to implement the solution. A variety of customer data sources, such as CRMs and point of sale systems, can be landed in a data lake storage account using orchestration tools in Azure such as Synapse Analytics and Data Factory for batch loads and Event Hubs and Delta Live Tables for streamed sources. Use of a Databricks lakehouse architecture makes it easier to combine multiple customer data types in a common storage account and structure the subsequent transformations according to a medallion pattern, with a bronze raw area, silver single customer view area with defined schema and a gold area for any analytical views or data science outputs, which can be dimensionally modelled for downstream use cases, such as the operational use of the data within CRM systems for marketing campaigns, customer analytics dashboards helping you to understand your customer base quantitatively and other applications built from customer data such as churn models or recommendation engines.

Cloud architecture for a single customer view-focused analytics and data science platform on Azure. https://learn.microsoft.com/en-us/azure/architecture/solution-ideas/articles/azure-databricks-modern-analytics-architecture edited with permission by the author.

By storing and processing customer data in the cloud, you delegate some responsibility for the security of customer data to the cloud service provider (e.g., Microsoft) and can use private networking of the Azure environment and elevated encryption standards wherever possible, to ensure the safeguarding of customer data. By configuring access controls, access to customer data can also be restricted, so that whilst a wide audience within a business may be able to view anonymised or aggregated customer data, raw customer data access can be limited to those in the business that need to use it for marketing purposes or solution maintenance, so that the risk of leaks is minimised.

Once curated, a single customer view opens the door to many data science applications such as customer profiling by demographics, customer lifetime value analysis or recency-frequency-monetary value analysis, market basket analysis (the analysis of buying patterns and the propensity of the co-purchasing of item sets), as well as ML modelling for churn prediction enabling timely email interventions such as discounts and offers to improve retention and recommendation engines which match customers with products they are most likely to buy at a particular point in time during the customer lifecycle. Other analytics applications of a single customer view include the dashboarding of aggregated customer data to understand buying trends and seasonality, and text analytics over customer feedback to understand areas a business can improve service; a single customer view is also intrinsically useful from an operational perspective within a CRM system, as it will increase the efficiency of marketing campaigns and other interventions, particularly where the cost of contacting the customer is elevated, such as postal marketing or cold-calling/SMS messaging, by minimising contacts to duplicate customers or out of date addresses/phone numbers.


Using open-source tools, Databricks and other Azure components it is possible to build a cost-effective and scalable single customer view and deploy it to the cloud in a secure and compliant wayThe proposed solution is high code, requires domain expertise and involves some decision making on the part of the data steward to cleanse and perform linkage over disparate customer datasetsHowever, the solution also has numerous advantages over commercial offerings, in terms of lower licensing fees and running costs, solution customisability and convenient integrations with other cloud components for deploying analytics and data science uses casesA single customer view opens the door to a variety of impactful data science and analytics use cases which can help a business market more efficiently, understand their customers and deliver better service

Thanks for reading and if you’re interested in discussing or reading further, please get in touch or check out some of the references below.



[1] https://www.informatica.com/content/dam/informatica-com/en/collateral/white-paper/improve-service-with-single-view-of-customer_white-paper_2446.pdf

[2] https://www.experian.co.uk/assets/about-us/white-papers/single-customer-view-whitepaper.pdf

[3] https://www.databricks.com/blog/2022/03/23/implementing-the-gdpr-right-to-be-forgotten-in-delta-lake.html

[4] https://docs.greatexpectations.io/docs/

[5] https://gdpr-info.eu/

[6] https://docs.databricks.com/en/security/privacy/gdpr-delta.html

[7] https://github.com/moj-analytical-services/splink

[8] https://www.informatica.com/blogs/golden-record.html

[9] https://learn.microsoft.com/en-us/azure/architecture/solution-ideas/articles/azure-databricks-modern-analytics-architecture

Building a Single Customer View Using Open-Source Tools and Databricks was originally published in Towards Data Science on Medium, where people are continuing the conversation by highlighting and responding to this story.

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