Don't "roll over" work
Basic
difficulty
Stage 2
Agile IQ® Level
Estimation
Metrics
Introduction
When work doesn’t get finished in a Sprint, the temptation is to “roll it over” into the next Sprint. A better approach is to learn to slice work so that it does fit into a Sprint.
Slicing Backlog items like a cake – thin, vertical slices, is considered “best practice”.
Waterfalling Sprints
When work extends beyond the Sprint boundary it’s often because tasks, such as development or testing, continue til they’re finished instead of being able to be completed within the boundaries of the Sprint.
This is called ‘Waterfalling your Sprints’.
Improve your estimation
If the item can’t be delivered in a single Sprint, then the team needs to break it down into smaller pieces. Each slice needs to be able to be completed, and achieve the Definition of Done, by the end of the Sprint.
Don't Waterfall your Sprints
If you're breaking up Backlog items by task, so that you're doing development in one Sprint and then testing in another, you're Waterfaling your Sprints. Try, instead, to break up large backlog items by Feature. This is known as 'vertical slicing''.
Vertical Slicing
What is vertical slicing?
The term “vertical slice” refers to a cross-sectional slice through the layers that form the structure of the software code base. It is mostly used in Scrum where the work is planned in terms of features. For example, as a very basic approach, a software product may consist of three layers (or components):
- Data access layer (bottom)
- Business logic layer (middle)
- User interface layer (top)
Why not use 'horizontal' slicing?
Horizontal slicing has a number of disadvantages to vertical slicing.
- Reduced transparency: Progress isn’t visible to customers until the last slice is delivered and integrated.
- Higher dependencies: Each layer is dependent on the previous layer. If an error isn’t found until the UI layer is delivered, rework might extend all the way back to the database layer.
This makes vertical slicing a preferred practice over horizontal slicing.
Slice large PBIs like cake
This is where the ‘multi-layer cake’ metaphor was born. First espoused by Bill Wake (2003), he suggests:
Think of a whole system as a multi-layer cake, for example, a network layer, a persistence layer, a logic layer, and a presentation layer. When we split a story, we're serving up only part of that cake. We want to give the customer the essence of the whole cake, and the best way is to slice the cake vertically through the layers. Developers often have an inclination to work on only one layer at a time (and get it 'right'), but a full database layer (for example) has little value to the customer if there is no presentation layer.
How small should the slices be?
While there is no ‘perfect’size for a Backlog item, to promote the best transparency possible, try slicing a Backlog item so that it can be delivered against the Definition of Done in 2-3 days.
References
1. Wake, B. (2003). INVEST in Good Stories, and SMART Tasks. Xp123. Online at: https://xp123.com/articles/invest-in-good-stories-and-smart-tasks/