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Number of Object Relative Reuse Number of Object Relative Reuse
methods type size categoriesmethods type size categories
Identify objectsIdentify objects
Number of Object Relative Reuse Number of Object Relative Reuse
methods type size categoriesmethods type size categories
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
1. Prepare a conceptual 1. Prepare a conceptual design (objects and design (objects and methods + their methods + their function)function)
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
2. For each object 2. For each object assign its assign its typetype..
Skyscraper Church GarageSkyscraper Church Garage
• LogicLogic
• I/OI/O
• TextText
• CalculationCalculation
• DataData
• Set-upSet-up
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
3. For each object 3. For each object assign one of assign one of size size ranges.ranges.
Very big Big Medium Small Very smallVery big Big Medium Small Very small
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
4. Knowing:4. Knowing:• programming languageprogramming language• object typeobject type• size rangessize ranges• the number of methodsthe number of methods
estimate, using historical estimate, using historical data, size of each object.data, size of each object.
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
5. Determine initial 5. Determine initial program estimated program estimated size, X, adding the size, X, adding the values received in the values received in the previous step.previous step.
2 + 3 = 52 + 3 = 5
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
6. Apply linear 6. Apply linear regression to get regression to get estimated program estimated program size Y:size Y:
Y = Y = 11 X + X + 00
5 means 105 means 10
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
xxi i yyii - n x - n xavgavg y yavgavg
xxii22 - n x - n xavgavg
22 11 = =
00 = y = yavgavg - - 11 x xavgavg
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
7. Using the 7. Using the t distributiont distribution and and standard standard deviationdeviation compute the compute the prediction intervalprediction interval for for a given percentage. a given percentage.
For 100% theFor 100% the
interval isinterval is
[0; + [0; + ]]
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
7a. Calculate the standard deviation, 7a. Calculate the standard deviation, , of , of your historical data around the your historical data around the regression line.regression line.
1122 = (y = (yii - - 00 - - 11xxii))22 n-2n-2
i=1i=1
nn
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
7b. To find the two-sided value of 7b. To find the two-sided value of tt for the for the probability probability qq, look in a table of the , look in a table of the tt distribution under distribution under p(p()= (1+q)/2)= (1+q)/2 and and n-2n-2 degree of freedom.degree of freedom.
J. Nawrocki, DPP, Wykład 8
The t distributionThe t distribution
Degrees p()=.6 p()=.7 p()=.85 p()=.9
5 .267 .559 1.156 1.476
6 .265 .553 1.134 1.440
7 .263 .549 1.119 1.415
8 .262 .546 1.108 1.397
9 .261 .543 1.100 1.383
J. Nawrocki, DPP, Wykład 8
Probe methodProbe method
(X - x(X - xavgavg))22
(x(xii - x - xavgavg))22++
11
nn++11 Range = Range = tt
7c. Compute the range as follows:7c. Compute the range as follows:
Initial estimateInitial estimateobtained in Step 5obtained in Step 5
4. Effort4. Effortminmin = Effort - Range = Effort - Range
J. Nawrocki, DPP, Wykład 8
SummarySummary
Size estimation is a basis for Size estimation is a basis for effort estimation and planningeffort estimation and planning
The Probe method:The Probe method:• Historical data are needed.Historical data are needed.• Statistical methods are used.Statistical methods are used.• Programmer obtains not only Programmer obtains not only
the estimate but also a the estimate but also a prediction interval.prediction interval.
J. Nawrocki, DPP, Wykład 8
Further readingsFurther readings
W. Humphrey, A Discipline for W. Humphrey, A Discipline for Software Engineering, Addison-Software Engineering, Addison-Wesley, Reading, 1995, Chapter 5.Wesley, Reading, 1995, Chapter 5.
J. Nawrocki, DPP, Wykład 8
Quality assessmentQuality assessment
1. What is your general 1. What is your general impression ? (1 - 6)impression ? (1 - 6)
2. Was it too slow or too fast ?2. Was it too slow or too fast ?
3. Did you learn something 3. Did you learn something important to you ?important to you ?
4. What to improve and how ?4. What to improve and how ?