With these additional states the product cumulative flow diagram radiates a lot of information. It shows the entire product backlog in terms of story point estimates and the state of the backlog over time. A typical (idealised) cumulative flow diagram is shown below for a completed project. This diagram gives an indication of velocity, product scope changes, effectiveness of the grooming process, and the size of the work in progress, all in one picture.
The project should start with a large backlog of ‘Not Done’ PBIs with a small set of these ‘Ready’ for development. During each sprint some of these Ready PBIs will be assigned to the sprint and will be worked on, setting them to ‘In Dev’. Ideally within the sprint these will move to ‘In Test’, be tested, and marked as ‘Done’. Sometimes work in progress will be carried over to the following sprint. At the end of each sprint some new PBIs will be added to the backlog during the sprint review. Within each sprint some time should be dedicated to ensuring there are enough ‘Ready’ PBIs for the following sprints to work on, this may require breaking down large PBIs and re-estimating the pieces. SfTS in TFS can generate the cumulative flow diagram automatically, and this can be used to indicate potential problems with the project. For example:
- PBIs not being created or estimated early enough in the release – the curve should rise steeply at the beginning and then level off with one or two stories being added at sprint review, and fluctuations in the size of the project when large PBIs are broken down into more detailed ones. Towards the end of the release the height may even reduce if PBIs are de-scoped from the release
- If testing is delayed (not performed within the sprint) then the ‘In Test’ work will accumulate – if this happens expect a late surge of PBIs / Bugs when the testing does start
- The diagram should display obvious cycles – In Progress / In Test work should approach zero at sprint boundaries
- At minimum the rate of items moving from ‘Not Done’ to ‘In progress’ should be matched by the rate of items being moved from ‘In Progress’ to ‘Done’ – testing should keep up with development.
- If too little grooming is being done the Ready PBIs will drop close to the In Progress line
- If too much grooming is being done the Ready PBIs will rise up towards the Not Done line – ideally there should be between 2 and 3 sprints worth of Ready PBIs at any one time.