1CS 350: Introduction toSoftware EngineeringSlide Set 3Estimating with Probe IC. M. OverstreetOld Dominion UniversitySpring 2006Fall 2005 CS 350/ODU 2Reading assignments Though Chapter 6 (PROBE) Text has many more examples than we’re able to do in class! And it’s much easier to see how the plan data go onto the PSP formsLecture Topics Planning overview Why estimate size? Size estimating principles The PROBE estimating method Size estimating proxies Estimating examples2Planning Overview Plans  allow you to make commitments that you can meet provide the basis for agreeing on job scope, schedule, and resources guide the work facilitate progress tracking and reporting help ensure that key tasks are not overlooked The Project Planning FrameworkProductdeliveryTrackingreportsDefinerequirementsProduceconceptualdesignEstimatesizeEstimateresourcesProducescheduleDevelopproductSize, resource,scheduledataProcessanalysisResourcesavailableSizedatabaseProductivitydatabaseThe Planning Process Before making the plan, you must have a requirement. The better the requirement, the better the plan. With ill-defined requirements, expect to make frequent plan updates. Plans are most accurate when based on size estimates and appropriate historical data.  With a size estimate and historical data, you can identify the data on the most similar prior work base the resource estimate on these data3Size Estimating Principles - 1 Estimating is an uncertain process. No one knows how big the product will be. The earlier the estimate, the less is known. Estimates can be biased by business and other pressures. Estimating is an intuitive learning process. Ability improves with experience and data. Some people will be better at estimating than others. Estimating is a skill. Improvement will be gradual. You may never get very good. The objective is to become consistent. You will then understand the variability of your estimates. You seek an even balance between under- and overestimates.Size Estimating Principles - 2Fall 2005 CS 350/ODU 9PSP 0PSP 1PSP 2Effort Estimation Accuracy100%0%-100%-200% 100%0%-100%-200%0204002040100%0%-100%-200% 100%0%-100%-200%0204002040100%0%-100%-200% 100%0%-100%-200%0204002040Balanced Estimates  Majority are under-estimating Balance of over-and underestimates Much tighter balance around zero4 The advantages of using defined estimating methods are that you have known practices that you can improve have a framework for gathering estimating data can consistently use historical data to produce balanced estimatesSize Estimating Principles - 3 The PSP uses the PROBE method to estimate and plan projects. PROBE stands for PROxy Based Estimating. PROBE uses proxies to estimate program size and development time. A good proxy will help you to make accurate estimates.Estimating with PROBEThe PROBE Estimating MethodConceptualdesignStartIdentify and size the proxiesNumber ofitemsPartTypeRelativesizeReusecategoriesEstimate other element sizesEstimateprogram sizeCalculateprediction intervalSize estimateand rangeEstimateresourcesCalculateprediction intervalResource estimateand range5Conceptual Design - 1 The first estimating step is to make a conceptual design. relate the requirements to the product define the product elements that will produce the desired functions estimate the size of what you plan to build For most projects, the conceptual design can be produced relatively quickly.  For the PSP exercise programs, try to limit your conceptual design time to 10, or at most 20, minutes.Conceptual Design - 2 To make a conceptual design, identify the product functions and the program parts needed to produce them. In effect, you say: “If I had the following parts, I could build this product.” Then, compare these parts to programs you have already written and estimate their sizes. Finally, combine the part estimates to give total size. If you do not understand the product well enough to make a conceptual design, you do not know enough to make a plan.Size Estimating Proxies - 1 The basic issue Good size measures are detailed. It is generally hard to visualize product details early in a project.  Alternatives Wait to estimate until you have the detail. Make your best guess. Identify a suitable proxy.6Size Estimating Proxies - 2 A good proxy should correlate closely to development costs. A good proxy should be easy to visualize early in development. It should also be a physical entity that can be measured.Fall 2005 CS 350/ODU 17Example: Building Costs Problem The builder needs to know the floor area (in sq. ft.) to estimate the cost of construction. Clients normally cannot describe their needs in square feet.  They usually can describe the type and number of rooms they want. Solution Use rooms as a proxy for size. Use historical (typical) data to translate from rooms to square feet.Fall 2005 CS 350/ODU 18Example: Customer Requirements Bedrooms: 1 large, 2 medium, and 1 small Bathrooms: 1 large and 2 medium Kitchen: 1 medium Living room: 1 large Dining room:1 medium Family room:1 large Utility: 1 medium7Fall 2005 CS 350/ODU 19Historical Building Data805025Utility340240150Family rooms200140100Dining rooms400250150Living rooms160130100Kitchens1206025Bathrooms20014090BedroomsLargeMediumSmallFall 2005 CS 350/ODU 20Proxy Calculation90=901 x=1 smallBedroom50340140400130601201402001870=Total (sq. ft.)50=1 x=1 mediumUtility340=1 x=1 largeFamily room140=1 x=1 mediumDining room400=1 x=1 largeLiving room130=1 x=1 mediumKitchen120=2 x=2 mediumBathroom120=1 x=1 largeBathroom280=2 x=2 mediumBedroom200=1 x=1 largeBedroomExample: The Builder’s Estimate  The first estimation step provides the builder with the proxy data for room size. However, there are many other cost elements in home construction. Builders typically have extensive data to relate room size to the other building costs. With agreed initial plans, builders typically require detailed architectural specifications and estimates before quoting a price.8Example Product Proxies  Classes, functions, and procedures Product elements database elements screens, reports, scripts, files book chaptersClasses as Proxies - 1 Correlation with development hours Numbers of classes correlates reasonably