Learning Objectives
By the end of this lesson you will be able to:
- Explain what legacy decommissioning involves and why it is the ultimate objective of a data migration
- Describe the logical and physical dimensions of decommissioning
- Identify the conditions required before a decommissioning certificate can be signed
Decommissioning as the Business Case
Legacy decommissioning is not the end of the project - it is the reason for the project.
The original business case for a data migration is almost always about retiring legacy systems: reducing licence costs, eliminating maintenance overhead, freeing staff from maintaining outdated technology, consolidating data centres. If the legacy systems are never decommissioned, the business case is never realised.
PDM treats decommissioning as a first-class project objective. Every SRP, every BTR, every DQR item is ultimately in service of the moment when the Data Owner signs the decommissioning certificate.
Logical vs. Physical Decommissioning
Logical decommissioning is the business decision that a legacy system is no longer needed for production purposes. The data has been migrated, validated, and accepted. The system will no longer be updated with business data.
Physical decommissioning is the technical act of shutting down the system, removing access, and archiving or destroying the data according to the retention policy.
The two are separated in time:
- Logical decommissioning happens when the Data Owner signs the certificate, often during or shortly after the hypercare period
- Physical decommissioning may follow months later, after the retention period has been satisfied and access rights have been revoked
Conditions for Decommissioning
The decommissioning certificate is only signed when the conditions defined in the SRP are met:
Data conditions:
- All agreed data has been migrated to the target or archived
- The Data Owner has reviewed migrated data and is satisfied with its quality
- Any required data audit/lineage reports have been produced
Operational conditions:
- Business users are trained on the target system
- No current business processes depend on the legacy system for live data
- Transitional Business Processes for in-flight transactions have been completed
- Any data retained in the legacy for reference purposes has been archived accessibly
Technical conditions:
- All access to the legacy system has been revoked except archival read access
- The archive is secured and accessible for the required retention period
- Data lineage documentation allows migrated records to be traced to their source
Legacy Decommissioning as Business Engagement
The decommissioning certificate process is the final Super Smart Task. Getting a Data Owner to sign requires:
- Building the relationship through the BTR process (they defined the conditions)
- Delivering the migration against those conditions
- Providing evidence that the conditions are met
A Data Owner who has been through this process - who had their concerns heard and documented, who saw those concerns addressed in the migration design, who reviewed the migrated data in trial runs - is well-prepared to sign.
A Data Owner who has had the migration “done to them” will find reasons to delay indefinitely. Protecting the legacy system is always psychologically easier than signing it away.
PDM’s entire Business Engagement workstream exists to create the conditions for the decommissioning certificate to be signed on time.
Decommissioning Report
The legacy decommissioning is documented in a Decommissioning Report, which is a programme-level configurable item capturing:
- Which systems have been decommissioned and when
- Who signed the decommissioning certificate
- What archive has been created and where it is held
- What retention period applies to the archive
- The final migration statistics for the decommissioned system
The Decommissioning Report is the formal programme record that the business case has been realised.
Key Takeaways
- Legacy decommissioning is the business case for the migration - not the end of the project
- Logical decommissioning (business sign-off) precedes physical decommissioning (technical retirement) by weeks or months
- The decommissioning certificate conditions are defined in the SRP and built into the migration design from the start
- The entire PDM Business Engagement workstream is designed to make the decommissioning certificate achievable
Book Reference
Practical Data Migration by Johny Morris (BCS, The Chartered Institute for IT):
- Chapter 14 - Legacy Decommissioning