Learning Objectives
By the end of this lesson you will be able to:
- State and explain the four Golden Rules of PDM
- Explain why each rule exists and what happens when it is violated
- Apply the Golden Rules to evaluate a migration approach
The Four Golden Rules
The Golden Rules encapsulate the underlying philosophy of PDM. They are not aspirational principles - they are practical constraints that shape every decision in a migration project.
Rule 1: Data Migration is a Business Issue, Not a Technical Issue
The most common framing of a data migration is as an IT project with some business involvement. IT extracts the data, transforms it, loads it. The business reviews it afterwards.
PDM inverts this. The business owns the data. The business knows what the data means. The business has to sign off that the migrated data is correct before the legacy system can be decommissioned.
This does not mean IT has no role - it means the business cannot be a passive stakeholder. The Responsibility Gap (lesson 2) is what happens when Rule 1 is violated.
Rule 2: The Business Knows Best
Within the enterprise is all the knowledge you will ever need to migrate the data correctly. Not in the database schemas, not in the data profiling tools, not in the ETL logs - in the people who work with the data every day.
The corollary: no amount of technical analysis substitutes for business knowledge. A rule of thumb in PDM is that you can model the data, normalise the data, and pattern-match the data - but you cannot know whether the result represents business reality without involving the people who know that reality.
This is why Business Domain Experts (BDEs) - frontline staff with day-to-day contact with specific legacy systems - are a formal role in PDM, not an afterthought.
Rule 3: No Organisation Needs, Wants or Will Pay for Perfect Quality Data
This rule is often the hardest for people from a data quality background to accept.
Data migration is a project, not a process. It has a deadline and a business case. Achieving 100% data quality before migration is almost never possible, and in most cases is not necessary - what the business needs is appropriate quality for the target system and the business processes it will support.
PDM does not ignore data quality. It manages it. The Data Quality Rules (DQR) process provides a structured way to prioritise, track, and resolve data issues - with business-led prioritisation at its centre.
The practical implication: if you can’t count it, it doesn’t count. That is the fourth rule.
Rule 4: If You Can’t Count It, It Doesn’t Count
PDM is product-based and measured. Every data quality issue is quantified - how many records are affected, what percentage of the total, what is the impact on the migration.
Qualitative assessments (“there are some quality issues in the customer data”) are not actionable. Quantitative assessments (“437 of 12,000 customer records are missing a mandatory field, representing 3.6% of the total, with 80% of those in the legacy CRM system”) are.
This rule drives the DQR process, the System Retirement Plans, and the migration readiness dashboard. Progress is measured and reported in numbers.
How the Rules Work Together
The four rules are not independent. They reinforce each other:
- Rule 1 (business issue) establishes that the business must own the migration
- Rule 2 (business knows best) explains why - business knowledge is irreplaceable
- Rule 3 (no perfect quality) sets realistic expectations and prevents analysis paralysis
- Rule 4 (if you can’t count it) ensures that “appropriate quality” is measurable, not just declared
A project that violates Rule 1 will almost certainly violate Rules 2 and 4 as a consequence, and will end up with either a failed migration or a permanent legacy system.
Key Takeaways
- The four Golden Rules are: (1) business issue not technical; (2) business knows best; (3) no perfect quality needed; (4) measure everything
- Rule 1 is the most commonly violated - and its violation is the root cause of most migration failures
- Rule 3 is the most counterintuitive - but it is essential to making a migration time-bounded and deliverable
- Rule 4 is what makes Rules 1-3 operational - measurement is how business ownership becomes real
Book Reference
Practical Data Migration by Johny Morris (BCS, The Chartered Institute for IT): Chapter 2, “Golden Rules and Super Smart Tasks”.