Using Line of Balance to Track the Progress of Fixing Trouble Reports
By: Eduardo Miranda
You are the project manager of a large project and testing is uncovering faults, trouble reports are starting to pile up and the release date is coming soon. Are they going to be fixed on time? What could you do to help? Are there any bottlenecks? Where should you assign more resources? Does this scenario sound familiar? Have you been there? This article will explain how you can answer these questions by using an old method called Line of Balance in a new way.
Line of balance (LOB) was devised by the members of a group headed by George E. Fouch during the 1940’s to monitor production at the Goodyear Tire & Rubber Company . It was also successfully applied to the production planning and scheduling of the huge Navy mobilization program of World War II and during the Korean hostilities. Today, LOB application has been further expanded, making it suitable for a whole spectrum of activities ranging from research and development through job-shop and process flow operations.
In the context of managing a software project, the LOB technique offers two main advantages over the traditional Open Trouble Reports (TRs) Chart :
* It allows project managers to see, in the middle of a project, whether they can meet the schedule if they continue working as they have been.
* It exposes process bottlenecks, allowing the project manager to focus on those points responsible for slippage.
The Open TRs Chart
To answer some of the questions raised at the beginning of this article, project managers usually resort to the Open TRs Chart shown in Figure 1 or a variation of it.
The Open TRs Chart shows the cumulative number of TRs written over time, and its breakdown into open and closed TRs. As the project progresses, the closed line should converge toward the total line and the open line towards zero. A closed line that is not converging fast enough toward the total or an open line that does not approach zero signals to the project manager the need to devote additional resources to fix problems.
Variations of the chart include showing a more detailed breakdown of the TR status, and ratios between total and open TRs [2, 3].
Despite all its usefulness, the Open TR Chart lacks predictive ability and fails to take advantage of past and present performance data and TRs closure targets; i.e., how many TRs should be in a given state by a given time to meet the project deadlines. In other words, although the chart will give the project manager a gut feeling about the situation, it would not answer the questions of where are we in relation to where we are suppose to be, or how much better we should be doing to get where we want to get by the time we want.
The TR Life Cycle
Typically, a TR will go through a number of stages or states since it is reported until it is closed (see Figure 2). Each of these states corresponds to a milestone in the process of answering a TR into which the organization or project manager wants to have visibility to evaluate progress, i.e., how many TRs have been reported, how many of the reported TRs have been analyzed, how many of the analyzed were rejected and so on. Elemental states could be grouped into super sets for reporting purposes, i.e., while the project manager might be interested in how many have been analyzed, assigned, implemented, or integrated the steering group overseeing the project might only been interested in how many TRs were reported, how many were closed, and how many were still pending.
Most defect tracking systems will implement this model or some variation of it, time stamping each TR as they transition between states. This last feature would allow the organization to produce the lead-time information required by the LOB method.
In addition to the state and timing information, the TR includes other data such as the severity of the problem. This information could be used to filter the TR data and apply the LOB method to a subset of all the TRs reported and in the prioritization of which TRs to fix first.
The LOB Method Applied to TRs
The LOB method consists of the following elements :
* A number of control points and their lead times to closing as illustrated in Figure 3, at which progress is to be monitored.
* An Objective Chart or target plan displaying the cumulative closing schedule as planned by the project manager to meet a set deadline (Figure 4).
* The TRs Status Chart (see Figure 5), which shows the actual number of TRs that have passed through a given control point versus the number that should have been passed (the LOB) according to the plan.
The information contained in the Objective Chart, together with the lead-time information is used to calculate how many TRs should be in a given state at a given time.
In LOB terminology, a control point is a milestone or event that the project manager wants to monitor. In the context of tracking TRs, the control points and states in the TR life cycle would most likely coincide, but this is not necessary. For example, the project manager might not find it useful to track TRs in the rejected state and so this state would not be considered a control point. The lead time for a control point is calculated using the following formula:
LeadTimen = 0
LeadTimeq=n-1,n-2,...n-1 = TimeInStateq + LeadTimeq+1
Assuming that the median2 times a TR spends in a given state are those shown in Table 1, the lead-time calculations will yield the results illustrated in Figure 3.
The Objective Chart
The Objective Chart shows cumulative, to be verified TRs on the vertical scale and dates of achievement along the horizontal scale. The chart might also include a display of the achievements so far.
The Objective Chart in Figure 4 shows that the project manager has committed to close 50 TRs by the end of September, 80 by the end of November, and 150 by the beginning of the following year. The chart also shows that as of mid-December progress is slightly behind with the project delivering around 75 fixed TRs instead of the 80 promised.
TR Status Chart
The TR Status Chart provides quantitative information with regards to progress, and whether or not there is a bottleneck on the process.
The chart portrays the actual number of TRs that have passed through each control point against the number that should have been passed according to the plan. These last quantities are called the LOB. The difference between the LOB and the top of the bar for each control point is the number of TRs behind or ahead of schedule.
Notice that the shape of the LOB will change daily even if there are no new TRs reported, since its calculation depends on the planned curve of the Objective Chart and the status date.
The TR Status Chart shows that there are almost 180 TRs reported so far, 30 more than what were planned to fix according to the Objective Chart. This signals the need to update the plan. It also tells us that TR implementation is on track as the actual column and the LOB line for that control point coincide, but that we are falling behind in their integration and verification. This suggests that adding more people to implementation activities will not help recoup the delay, but that additional resources could be used in integration and verification activities.
The LOB for each control point is calculated as follows: The idea behind the procedure is simple. If it takes an average of 10 days for a TR to go from a given state to the completion state, today’s status for that state should be equal to the number of TRs that would have to be completed according to the plan 10 days from now. See Figure 6 for a graphical example.
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