Scrum in detail

What is Scrum?

Scrum is currently the most widely used framework to manage software projects (see Wikipedia: Scrum).

Since Scrum is so popular you will find many slightly varying implementations of Scrum in the real world. In this answer, I am trying to present what I consider to be the most common implementation of scrum.

Why did Scrum become so popular?

At its core, Scrum is based on an iterative feedback loop and time-boxed sprints (periods of planning & value creation).

Software development is very complex, it is extremely hard if not impossible to know how an ideal solution to a problem would look like upfront. On top of that, “what is ideal” tends to change over time.

Therefore, choosing an iterative approach to developing software to leverage information and insight gained on the fly is very pragmatic. It is also used in other disciplines with similar constraints (highly competitive, changing environment) like military reconnaissance (See Wikipedia: OODA loop).

On top of that most of the software that is written today is never ‘finished’. This is especially true for successful software. It is rather improved and maintained for extended periods of time (think decades).

Scrum is a better fit for the way we think of software today than other (more sequential) methodologies that came before Scrum (See Wikipedia: Waterfall model).

What are Scrum Sprints?

Scrum sprints are time-boxed periods where the software development team works on a set of items that need to be completed. A typical sprint length used to be about 2 months. Nowadays the common sprint lengths are usually around 1-2 weeks, trending to even shorter cycles.

Shorter sprint time-boxes make a lot of sense from a business point of view. They enable faster delivery & adaption to what’s going on in your market.

What is Scrum Sprint planning?

At the beginning of every sprint you plan which items (stories) should be worked on for the upcoming “sprint” time-box. Teams will then use estimates (based on complexity or expected time-to-completion) and the team performance of previous sprints (velocity).

So for example, if you know that during the previous 2-week sprints you were able to deliver about 4 ‘medium’-complexity items (stories) then you can take this (velocity) as your ballpark for how many items you take on in the upcoming sprint.

There are various ways to come up with a sprint velocity for your team. One common method is to ‘size’ items (stories) like t-shirts with a weighed complexity based on the Fibonacci sequence. For example:

• S (small) = 2 complexity
• M (medium) = 3 complexity
• L (large) = 5 complexity (might make sense to break up)
• XL (extra large) = 8 complexity (might make sense to break up)

What are Scrum Stand-Up Meetings?

A daily meeting where everyone in the team updates each other on what happened yesterday, what is lined up for today and whether there are any blockers.

These meetings usually are kept very short (around 15 minutes) and used to start the day.

What is a Scrum Sprint Retrospective?

The team reviews the work that got done during the sprint time-box and also examines the work that did not get finished. This is also the time to reflect on how to improve the overall software development process or tooling.

What is a Scrum Backlog?

The Scrum backlog is list of requirements that can range from ideas, features, bugs, higher level items as well as very granular quick fixes. Items in the Scrum backlog get estimated and ordered regularly.

The Scrum Backlog is the source of work items that will get considered for the next time-box in Sprint planning.