What ist a backlog, what types exist, how are they created and prioritised?
Backlog is a term meaning “an accumulation of something, especially uncompleted work or matters that need to be dealt with.” Or to put it simply: A backlog is a list of tasks or requirements that need to be done.
In software development and agile project management, different types of entries are managed in backlogs. These are called backlog items. The following items can be distinguished:
- functional requirement
- quality requirement
- user story
- job story
- use case and use case slice
Ideally, each backlog item should contain a description, a priority, an effort estimate and a customer benefit. The higher the priority of an item, the more precisely it is specified in practice. At the same time, the priority increases the probability that it will be processed or realised.
Management of Backlogs
The organisation of backlogs is structured differently in various companies. Usually there are three types of backlogs:
- Product Backlogs,
- Release Backlogs and
- Sprint Backlogs.
If different teams are involved in a development, it is a good idea to work with team backlogs and distribute the backlogs items accordingly among the respective team backlogs. If only one team is involved, then Release Backlog and Team Backlog are identical. Developers and employees can also maintain individual, personal backlogs.
The Types of Backlogs
The Product Backlog is the first container in which tasks to be completed, functional requirements, features etc. are recorded. In some organisations, the product backlog is also called a domain backlog – whenever organisations are active in different domains and it makes sense to record the backlog items per domain. A product backlog can be described by four properties:
- Prioritisation: The backlog items are prioritised.
- Detailing: A backlog item is described in detail the higher its priority is.
- Estimation: An effort estimate is performed for each backlog item. The higher the priority, the more accurate the estimate.
- Evaluation: A backlog item describes a customer benefit and this affects the prioritisation of the item.
The prioritisation of product backlog items is essential. Not all requirements are equally important, have the same customer benefit or cause the same effort for implementation. For example, prioritisation is carried out in Scrum by the product owner – ideally in close cooperation with the development team. The product owner is the contact person for the relevant stakeholders. While stakeholders often evaluate requirements with a view to a business value, the team pays attention to the development effort and a technically meaningful order of implementation. The use of relative values with Fibonacci figures is a good way of estimating costs. This has the advantage that expenses on a small scale can be estimated very precisely at the daily level (1 day, 2 days, 3 days, 5 days etc.), expenses on a large scale relatively roughly (e.g. 20 days, 40 days, 100 days etc.).
It should be noted that prioritisation must be carried out again and again because new requirements or the refinement of existing backlog items add new insights. A product backlog is therefore very dynamic and thus differs significantly from a requirement specification.
Agile projects are divided into releases and iterations. Since the time required for these iterations is relatively short with a recommended duration of one to four weeks, they are called sprints. They always have the same duration in a project. A defined number of sprints results in a release. Each company has to define both – duration and quantity – for itself. Example: After five sprints, there is the first release, after five more a next release, and so on. If there are several teams and parallel sprints, the intervals should be coordinated. Requirements are assigned to releases based on their priorities. Defining priority limits helps to distribute requirements to releases. If the product owner determines a lower limit of 802, then the items of the product backlog with priorities of 802 and higher are moved to the next release backlog, while requirements with priorities of 801 and lower are moved to later release backlogs.
In each sprint, a functional, potentially shippable intermediate product is to be developed. The sprint planning meeting decides which requirements from the release backlog are to be implemented in the next sprint. Requirements are to be implemented. The team selects the user stories with the highest priorities and estimates which and how many can be implemented within the next interval. The items to be implemented end up in the sprint backlog. The user stories are then divided into tasks that can be completed within one day. The development team independently determines who realises the tasks. In order to recognise the progress of the development, it is important to provide the tasks and subsequently the user stories with states. Once all tasks for the realisation of a user story have been completed, it is considered as realised. Taskboards or a user story mapping can be used for visualisation.
Prioritisation of Backlog Items
Methods for Prioritisation
The maintenance of backlogs is an important success factor for product development. With a well maintained backlog, you ensure that only requirements with the highest priorities are met. There are various methods for prioritising which can also be combined with each other:
- The Kano Model
The Kano Model classifies five characteristics that contribute to customer satisfaction in different ways: basic, performance and enthusiasm characteristics, as well as insignificant characteristics and rejection characteristics. Basic characteristics generate dissatisfaction when they are missing. Performance characteristics are an important factor for customer satisfaction and differentiation from the competition. And enthusiasm characteristics lead to disproportionate satisfaction.
- The MoSCoW Method
The MoSCoW Method distinguishes between functions that the development team should absolutely implement and those that could be implemented:
Must: Must-have functionalities that need to be implemented.
Should: Functionalities that have to be implemented after the must-have.
Could: Functionalities that can be implemented if they do not interfere with must-have or should functions.
Won’t: Functionalities that should not be implemented.
- Relative Weight Method
With the Relative Weight Method, each backlog item in the categories Advantages, Penalties, Risks and Costs is rated with a number from 1 to 9. The questions about the advantages (how big would the advantage be if a requirement were realised) and the penalties (how big would the penalty be if the requirement were not realised) are evaluated by the product owner together with the relevant stakeholders. And the questions about the risk (how high are implementation risks and dependencies on other teams and developments) and the costs for implementation are discussed by the product owner with his development team. The values for benefits and penalties are then divided by the values for risks and costs. The results are the basis for the prioritisation.
- Theme Screening
In Theme Screening, you identify up to nine evaluation criteria and then select a Baseline Theme, i.e. a user story that serves as the basis for a relative evaluation. It is recommended to select a backlog item that is familiar to the development team and should be implemented soon. You then rate the backlog items in the evaluation criteria as plus, minus or zero in relation to the baseline theme. Prioritisation is achieved by adding the plus and subtracting the minus values per item.
There are other methods like Rocks, Pebbles & Sand, Walking Skeleton or Theme Scoring. Which method is best suited for prioritising backlogs cannot be answered in general. Each company should make its own decision.
Challenges for Companies
Continuous Working with Backlogs
Backlogs are dynamic. New features, user stories or defects are added and stakeholders change their wishes. This results in new priorities on an ongoing basis. Regular maintenance is called backlog refinement or grooming. It ensures a high level of transparency, so that all project participants always know what is currently being worked on and what is coming up soon. A well-maintained backlog is at the heart of agile product development and ensures that companies can react quickly and flexibly to innovations. You can usefully supplement working with backlogs with a user story mapping.
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