This is the start of a series of articles about agile development. The motivation behind writing these articles is to expand my knowledge of the topic by explaining how I currently understand it. I imagine feedback from readers about their own experiences and understanding of the topics discussed could help my own comprehension of the material.
This entry focuses on some basic vocabulary used in the project management side of agile practices. The vocabulary presented here concentrates on requirement gathering, describing deliverables and estimation and will be used in later articles in this series.
The game team I am currently on use scrum (though purists would called it “scrum but”) which is common methodology adopted for managing time on an agile project. I have myself used “agile” style development practices like unit testing and continuous integration (using NUnit, Cruise Control .Net and Trac) in my past life outside of the games industry. I have made sure to make time to read about these agile practices for years.
Most of the week beginning 8th of February 2009 I took part in a lab called Agile Development in C# and I had a glimpse of techniques used in teams around the mother-ship. Spending the week building a project, managing the backlog and taking turns at being the scrum master and team lead was a very educational experience. “Living it” with guidance in this way was like a crucible of learning (there was an element of competition too). It was very rewarding yet quite draining!
My current lead developer attended the same course – thus I am more confident about “buy-in” of some agile practices at that level because of the extra common ground that brought me. I have already had the opportunity to apply some development techniques discussed in that course to the main code base I work with day to day.
Vocabulary: User Stories
User stories are requirements written from the perspective of the customer. A collection of user stories make up the “product backlog” and can be prioritised by how important they are to the user. This allows the developer to concentrate on things that would be immediately useful to the customer for when a vertical slice of the product is delivered at the end of the “sprint”.
A user story is an expression of what they want and why, rather than any technical detail of the how.
A good example might be: “I would like my lawn to be short so it is pleasant to lay back and read in the garden.”
A poor example might be: “Mow lawn to 2 cm using a rotary petrol mower.”
The user stories concentrate on requirement gathering and intent. These stories help communicate how the development team understand the requirements. They also allow quick feedback from the user on any good or bad assumptions made.
Vocabulary: Story Points
Story points were introduced as a way of quantifying an estimate of a user story. Where as estimates are usually expected as a duration, story points are based on an estimation of size and complexity.
For example a gardener might want to estimate the size of the lawn, see how overgrown it is and how much edge work would be necessary to keep it neat before attempting to estimate a time. Depending on weather conditions on the day, it may even take slightly longer on some days than others.
The customer expects a regular fee and period of time spent in the garden rather than taking in to account difficulties from one week to the next. One week the garden may not have grown very much and the whole thing will be quicker to complete. Perhaps the gardener might take the time to make nice little extra touches to the garden to add value that easier week where there is ample time left over.
So a story point is not directly translatable to time because of the various unknowns. The number of story points against something keeps track of how much effort will be required – something with more story points is harder to complete.
Tasks are derived from breaking a user story down in to small chunks of functionality. These tasks are estimated in hours (or story points). The estimated time remaining is updated daily during the scrum.
A task is only counted as “done” when it is verified. A consistent measurement of “done” is important so it can be signed off for the sprint. Quality gates can be used to measure if something is actually complete. This could include passing tests and automated code quality tools.
Once all the tasks for a user story have been completed, functionally tested and verified, then it can be taken from the product backlog.
For example tasks for large garden could be (in the form of Task (verify) – duration):
- Mow lawn (lawn appears visibly shorter. Regular straight lines can be seen in the grass) – 2 hours
- Tidy garden and rake lawn (no debris can be seen on the lawn or path, grass cuttings bagged and loaded) – 1 hour
Vocabulary: The Daily Scrum
The Daily Scrum is often a short morning stand-up meeting only including people doing the work itself. The scrum master role can be taken up by any member of the team. The scrum master asks the questions:
- What did you do?
- What will you do today?
- What is blocking you?
The estimates are updated on the current tasks, and the scrum master goes about trying to unblock the team where they are blocked. Blockages could be something technical, through to waiting on another team to complete a task.
Continuing the gardening example – if the gardeners have noticed the lawn mower blades have become blunt and causing the team to slow down, it would be up to the scrum master to communicate with the tools team and ask them to sharpen the lawn mower blades.
A selection of user stories are chosen for the sprint. Stories can be added or dropped from a sprint, but the deadline for a deliverable does not change. If the deliverable, demonstrable version of the software is created ahead of time and the team feels confident they can take another story from the backlog and if it’s too big, break it down where possible.
The idea of a sprint is to always have something to show for the work everyone has done at a regular interval, to allow the users to feed back. At the point a sprint begins, the requirements of the stories they are working on are locked. A sprint can be completely aborted, or a story dropped… but the requirements of an existing story should not change. The motivation is that the team are not aiming for a moving target and can concentrate on getting the unit of work done.
Ideally each sprint delivers a vertical slice to show progress. For the running gardening example I have been using – this might be completing the more simple front garden entirely to prove the gardeners have understood the requirements sufficiently to maintain the garden to the customer expectations. It also gives the customer an opportunity to feedback or change their mind “actually, I want my lawn to have circles rather than lines”.
Vocabulary Cheat Sheet
|Daily Scrum||Short stand-up meeting. What did you do? What will do today? What is blocking you?|
|Product backlog||Prioritised list of user stories.|
|Quality gate||Checklist of things to verify work against before it is counted as completed.|
|Scrum master||Leads daily scrum. Tracks work completed and remaining, and organises removal of things blocking the team. Ideally a role rotated between members of the team.|
|Sprint||A period of time where user stories are chosen to work on. External influences are not allowed to change the requirements of the stories being worked on. Sprints are a fixed length, but stories can be postponed or additional ones taken from the backlog.|
|Story points||Unit of estimation measuring complexity.|
|Task||A user story can be broken down in to one or more tasks. Tasks are estimated daily in hours (or story points) remaining by the developer working on them.|
|User stories||User requirements expressed in sentences from the customer perspective.|
|Vertical slice||Showing off a feature in an application that works from start to finish but may be limited in scope. For example a rope bridge crossing a chasm is immediately useful and allows people to cross. Having that in place can help to build a better bridge later.|
Some of my references are company confidential and cannot be shared here – the web is full of useful information though. The sites below are useful launch pads to further reading.
- Agile manifesto clearly states the priorities of an agile developer: http://www.agilemanifesto.org/
- Wikipedia has a good overview of scrum and vocabulary discussed here: http://en.wikipedia.org/wiki/Scrum_(development)
- Pragmatic Programmers (I’ve been a fan of their books for quite some time): http://www.pragprog.com
EDIT: Thought of a few more references:
- Jeromy Walsh via Joel Bennett’s blog for subconsciously planting the idea of a rope bridge I used in my vertical slice definition.
- Agile game development site: http://www.agilegamedevelopment.com/
- Laura Brandau’s blog about her experiences with Agile development: http://www.bridging-the-gap.com/
- Andy Barton recommended this to me the other day, but have not had a chance to look at it yet: http://www.infoq.com/minibooks/scrum-xp-from-the-trenches
Please comment any useful links you have stashed away :-)