What Is PDM?
Practical Data Migration (PDM) is a structured methodology for planning and executing data migrations. It was created by Johny Morris and published in book form through the British Computer Society. The third version, PDMv3, is the basis for this course.
PDM is not a software tool and it is not a generic project management framework adapted for data work. It is a methodology built specifically for the challenges that data migrations present - challenges that are different in kind from software development, business analysis, or infrastructure projects.
What Makes Data Migration Different
A data migration is defined in PDM as:
The selection, preparation, extraction, transformation and permanent movement of appropriate data which is of the right quality to the right place at the right time, and the decommissioning of Legacy Data stores.
Every word in that definition is deliberate. The definition highlights:
- Selection and preparation - not all data moves; deciding what moves requires business judgement
- Appropriate - quality is relative to purpose, not absolute
- Permanent - unlike system integrations, a migration is a one-way event
- Decommissioning - the legacy system must be retired; migration is not complete until this happens
These features combine to create a project type that is time-limited, irreversible, and heavily dependent on business knowledge that IT teams do not possess.
The PDM Framework
PDMv3 is organised around:
Two workstreams:
- Technical - analysis, mapping, ETL design, build and test
- Business Engagement - stakeholder management, data quality governance, transformation realisation
Nine modules:
| Module | Abbreviation | Description |
|---|---|---|
| Migration Strategy & Governance | MSG | Project framing, policies, governance |
| Landscape Analysis | LA | Discovering and documenting legacy data stores |
| Gap Analysis & Mapping | GAM | Mapping legacy data to target structures |
| Data Quality Rules | DQR | Managing and resolving data quality issues |
| Key Data Stakeholder Management | KDSM | Finding and engaging business data owners |
| Business Transformation Realisation | BTR | Capturing user requirements for the migration |
| Migration Design & Execution | MDE | ETL design, build, test and execute |
| Legacy Decommissioning | LD | Retiring legacy systems cleanly |
| Continuous Testing | CT | Testing woven throughout the project |
One sub-module: Release Management - governing the delivery of ETL releases in fortnightly cycles
One special zone: The DMZ - the contractual and operational boundary between client and supplier
Why PDM Works
The methodology is grounded in three observations about why migrations typically fail:
- The Responsibility Gap - data quality issues require business decisions, but projects do not give the business the structure to make those decisions at scale
- Late engagement - the business is not involved until problems are already critical, at which point cooperation is minimal and the deadline is close
- No decommissioning plan - without a commitment to retire the legacy system, migrations drag on indefinitely and the business case evaporates
PDM addresses all three directly. It makes IT-Business dependencies explicit from day one, builds business engagement into every deliverable through Super Smart Tasks, and treats legacy decommissioning as a first-class project objective.
Crucially, PDM does not do this by defining a cleaner or better-defined relationship between two separate sides. It removes the wall: the business and IT work as a single virtual team with shared ownership of the data. There are not two parties managing a relationship across a boundary - there is one team with one goal.
About the Author
Johny Morris spent over 20 years working for major systems integrators - including PwC, Logica CMG, and CSC - on large-scale data migration programmes. PDM was developed from direct project experience, not from theory.
The methodology has been applied to migrations across industries including utilities, manufacturing, financial services, healthcare, and public sector. The DHGS case study in this course is drawn from a composite of real projects.
Book Reference
Practical Data Migration by Johny Morris (BCS, The Chartered Institute for IT):
- Chapter 03 - PDMv3 Overview