The technique known as Gap Analysis is used throughout the TOGAF Architecture Development Method to validate an architecture under development. The main step to understand when undertaking a gap analysis is to consider any facets which may have been forgotten.
The purpose of a gap analysts is to show any shortcomings between the Baseline Architecture and the Target Architecture meaning any items which may have been accidentally or deliberately left out or not yet defined.
Crucial source of gaps which should be actively considered are any concerns of the stakeholders which may have not been addresses in prior architectural work.
A gap analysis occurs during phases B, C, D and E of the architectural development method.
How to perform a gap analysis
The first step is to draw a matrix with a list of all the Target Architecture Building Blocks (ABBs) across the top.
Next, create a new column listing all the Baseline Architecture Building Blocks (ABBs vertically)
At the end of the last horizontal row create a new column and call this column Eliminated.
Create a new row at the very bottom of the matrix and call this row New.
When an ABB appears in both the horizontal row at the top and the first column indicating that the ABB appears in both the target and baseline architectures, mark the cell as Included.
When an ABB in the baseline architecture is not included in the target architecture the ABB should be reviewed. In the scenario where the ABB is correctly eliminated mark it as Intentionally Eliminated in the associated cell in the Eliminated column.
When an ABB was found to be accidentally eliminated and must be addressed by reinstating it during the next iteration of the architecture design mark the ABB as Unintentionally Eliminated in the associated cell in the Eliminated column.
When an ABB from the target architecture is not included mark it as a gap which needs to be developed in the row marked New.