10.2.1 Purpose
The backlog is used to record, track, and prioritize remaining work items.
10.2.2 Description
A backlog occurs when the volume of work items to be completed exceeds the capacity to complete them.
Backlog management refers to the planned approach to determine:
- what work items should be formally included in the backlog,
- how to describe the work items,
- how the work items should be tracked,
- how the work items should be periodically reviewed and prioritized in relation to all other items in the backlog,
- how the work items are eventually selected to be worked on, and
- how the work items are eventually removed from the backlog.
In a managed backlog, the items at the top have the highest business value and the highest priority. These are normally the next items to be selected to be worked on.
Periodic review of the entire backlog should occur because changes in stakeholder needs and priorities may necessitate changes to the priority of some of the backlog items. In many environments, the backlog is reviewed at planned intervals.
The changes to the number of items in the backlog are regularly monitored. The root causes for these changes are investigated: a growing backlog could indicate an increase in demand or a drop in productivity; a declining backlog could indicate a drop in demand or improvements in the production process.
There may be more than one backlog. For example, one backlog may be used to manage a global set of items, while a second backlog may be used to manage the items that are due to be worked on within the very near future.
10.2.3 Elements
.1 Items in the Backlog
Backlog items may be any kind of item which may have work associated with it.
A backlog may contain, but is not limited to, any combination of the following items:
- use cases,
- user stories,
- functional requirements,
- non-functional requirements,
- designs,
- customer orders,
- risk items,
- change requests,
- defects,
- planned rework,
- maintenance,
- conducting a presentation, or
- completing a document.
An item is added to the backlog if it has value to a stakeholder. There may be one person with the authority to add new items to the backlog, or there could be a committee which adds new items based on a consensus. In some cases, the responsibility for adding new items may be delegated to the business analyst.
There may also be policies and rules which dictate what is to be added and when, as may be the case with major product defects.
.2 Prioritization
Items in the backlog are prioritized relative to each other. Over time, these priorities will change as stakeholders’ priorities change, or as dependencies between backlog items emerge. Rules on how to manage the backlog may also impact priority.
A multi-phased prioritization approach can also be used. When items are first added to the backlog, the prioritization may be very broad, using categories such as high, medium, or low. The high priority items tend to be reviewed more frequently since they are likely candidates for upcoming work. To differentiate between the high priority items, a more granular approach is used to specify the relative priority to other high priority items, such as a numerical ranking based on some measure of value.
.3 Estimation
The level of detail used to describe each backlog item may vary considerably. Items near the top of the backlog are usually described in more detail, with a correspondingly accurate estimate about their relative size and complexity that would help to determine the cost and effort to complete them. When an item is first added, there may be very little detail included, especially if the item is not likely to be worked on in the near term.
A minimal amount of work is done on each item while it is on the backlog; just enough to be able to understand the work involved to complete it. As the work progresses on other items in the backlog, an individual item’s relative priority may rise, leading to a need to review it and possibly further elaborate or decompose it to better understand and estimate its size and complexity.
Feedback from the production process about the cost and effort to complete earlier items can be used to refine the estimates of items still in the backlog.
.4 Managing Changes to the Backlog
Items make their way to the top of the backlog based on their relative priority to other items in the backlog. When new or changed requirements are identified, they are added to the backlog and ordered relative to the other items already there.
Whenever work capacity becomes available the backlog is reviewed and items are selected based on the available capacity, dependencies between items, current understanding of the size, and complexity.
Items are removed from the backlog when they are completed, or if a decision has been made to not do any more work on them. However, removed items can be re-added to the backlog for a variety of reasons, including:
- stakeholder needs could change significantly,
- it could be more time-consuming than estimated,
- other priority items could take longer to complete than estimated, or
- the resulting work product might have defects.
10.2.4 Usage Considerations
.1 Strengths
- An effective approach to responding to changing stakeholder needs and priorities because the next work items selected from the backlog are always aligned with current stakeholder priorities.
- Only items near the top of the backlog are elaborated and estimated in detail; items near the bottom of the backlog reflect lower priorities and receive less attention and effort.
- Can be an effective communication vehicle because stakeholders can understand what items are about to be worked on, what items are scheduled farther out, and which ones may not be worked on for some time.
.2 Limitations
- Large backlogs may become cumbersome and difficult to manage.
- It takes experience to be able to break down the work to be done into enough detail for accurate estimation.
- A lack of detail in the items in the backlog can result in lost information over time.
