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<h2 class="first-section-title"><a name="90"></a><a name="ch03lev1sec3"></a>An Algorithm for Estimating</h2><p class="first-para">It should be noted that technical architects are responsible for estimating hours only. Project managers should be equipped to account for absences due to responsibilities to other projects and vacation.</p>
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<b class="bold">Step 1: Determine the number of screens, interfaces, database tables, and</b> <b class="bold">conversions for each use case.</b> To derive a coding and unit-testing estimate, gather estimates of the following for the group of use cases being considered for the project:</p>
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<p class="first-para">Screens in the user interface (two man-weeks each)</p>
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<p class="first-para">External application interfaces (four man-weeks each)</p>
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<p class="first-para">Database tables (two man-weeks each)</p>
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<p class="first-para">Tables or files conversioned (two man-weeks each)</p>
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<p class="para">Not all these items will exist for each use case. The basic estimates noted in parentheses in the preceding list are applicable if the development team hasn't been formed; if there is an existing team, more accurate estimates for each item may be possible. Estimates at this point will not be exact. Estimating <a name="91"></a><a name="IDX-30"></a>based on the number of objects is more accurate, but that number is not available before object modeling exercises are done.</p>
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<b class="bold">Step 2: Estimate coding and unit-testing time for each use case.</b> Based on the information gathered in step 1, it's simple mathematics to get a base estimate for a combination of use cases. The <i class="emphasis">base estimate</i> is the length of time it takes for one developer to complete coding and unit-testing tasks. It may seem a bit strange to estimate coding and unit-testing time before design is complete. Few developers seem to be bothered by this ambiguity.</p>
<p class="para">Many developers confuse unit testing with system testing. Unit testing is strictly at a class level. How well a class functions when called from other classes within the application is system testing, not unit testing.</p>
<p class="para">For example, for a set of use cases that involves four screens, two external interfaces, five database tables, no data conversions, and two environment setups, the base estimate is:</p>
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