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Effort Estimation

Effort Estimation

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Effort Estimation

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  1. Effort Estimation • In WBS ,one can estimate effort (micro-level) but needed to know: • Size of the deliverable • Productivity of resource in producing that deliverable Effort = Size / Productivity e.g. Effort = 500 loc / (100 loc/person-day) = 5 person-days

  2. Effort Estimation (in General) For example? • Has been an “art” for a long time because • many parameters to consider • unclear of relative importance of the parameters • unknown inter-relationship among the parameters • unknown metrics for the parameters • Historically, project managers • consulted others with past experiences • drew analogyfrom projects with “similar” characteristics • broke the projects down to components and used past history of workers who have worked on “similar”components; then combined the estimates What if you are new at this and have no dependable contacts ?

  3. General (MACRO)Model • There have been many proposed models for estimation of effort in software. They all have a similar general form: • Effort ≡ (product size) & (other influencing factors) or more formally • Effort = [a + (b * ((Size)**c))] * [PROD(f’s)] • where : • Size is the estimated size of the project in loc or function points • a, b, c, are coefficients derived from past data and curve fitting • a = base cost to do business regardless of size • b = fixed marginal cost per unit of change of size • c = nature of influence of size on cost • f’s are a set of additional factors, besides Size, that are deemd important • PROD (f’s) is the “multiplicative product” of the f’s

  4. COCOMO (macro) Estimating Technique • Developed by Barry Boehm in early 1980’s who had a long history with TRW and government projects (initially LOC based) • Later modified into COCOMO II in the mid-1990’s (FP included for size, besides LOC) • Included process activities : • Product Design • Detailed Design • Code and Unit Test • Integration and Test • Utilized by some but many people still rely on experience and/or own company proprietary data. (some use COCOMO as a companion estimate) Note that requirements gathering and spec. are not included

  5. Basic Form for Effort • Effort = A * B * (size ** C) • or more “generally” • Effort = [A * (size**C)] * [B ] • Effort is in “person-months” • A = scaling coefficient • B = coefficient based on 15 parameters • C = a scaling factor for process • Size = delivered source lines of code in “KLOC”

  6. Basic form for Time • Time= D * (Effort ** E) • Time = total number of “calendar months” • D = A constant scaling factor for schedule • E = a coefficient to describe the potential parallelism in managing software development Past experiences indicate that “time estimate” has usually been more than actual

  7. COCOMO I • Originally based on 56 projects • Reflecting 3 modes of projects • Organic : less complex and flexible process • Semidetached: average complexity project • Embedded: complex, real-time defense projects

  8. 3 Modes are Based on 8 Characteristics • A. Team’s understanding of the project objective • B. Team’s experience with similar or related project • C. Project’s needs to conform with established requirements • D. Project’s needs to conform with established interfaces • E. Project developed with “new” operational environments • F. Project’s need for new technology, architecture, etc. • G. Project’s need for schedule integrity • H. Project’s size range

  9. Understand requirement Exp. w/similar project Conform w/req. Conform w/int. New oper. env. New tech/meth. Schedule int. Size

  10. COCOMO I • For the basic forms: • Effort = A * B *(size ** C) • Time = D * (Effort ** E) • Organic : A = 3.2 ; C = 1.05 ; D= 2.5; E = .38 • Semidetached : A = 3.0 ; C= 1.12 ; D= 2.5; E = .35 • Embedded : A = 2.8 ; C = 1.2 ; D= 2.5; E = .32

  11. Coefficient B • Coefficient B is an effort adjustment factor based on 15 parameters which varied from very low, low, nominal, high, very high to extra high • B = product (15 parameters) • Product attributes: • Required Software Reliability : .75 ; .88; 1.00; 1.15; 1.40; • Database Size : ; .94; 1.00; 1.08; 1.16; • Product Complexity : .70 ; .85; 1.00; 1.15; 1.30; 1.65 • Computer Attributes • Execution Time Constraints : ; ; 1.00; 1.11; 1.30; 1.66 • Main Storage Constraints : ; ; 1.00; 1.06; 1.21; 1.56 • Virtual Machine Volatility : ; .87; 1.00; 1.15; 1.30; • Computer Turnaround time : ; .87; 1.00; 1.07; 1.15;

  12. Coefficient B (cont.) • Personnel attributes • Analyst Capabilities : 1.46 ; 1.19; 1.00; .86; .71; • Application Experience : 1.29; 1.13; 1.00; .91; .82; • Programmer Capability : 1.42; 1.17; 1.00; .86; .70; • Virtual Machine Experience : 1.21; 1.10; 1.00; .90; ; • Programming lang. Exper. : 1.14; 1.07; 1.00; .95; ; • Project attributes • Use of Modern Practices : 1.24; 1.10; 1.00; .91; .82; • Use of Software Tools : 1.24; 1.10; 1.00; .91; .83; • Required Develop schedule : 1.23; 1.08; 1.00; 1.04; 1.10;

  13. An example Any problem? • Consider an averag e(semidetached) project of 10Kloc: • Effort = 3.0 * B * (10** 1.12) = 3 * 1 * 13.2 = 39.6 pm • Where B = 1.0 (all nominal) • Time = 2.5 *( 39.6 **.35) = 2.5 * 3.6 = 9 months • This requires an additional 8% more effort and 36% moreschedule time if we include product plan and requirements: • Effort = 39.6 + (39.6 * .08) = 39.6 + 3.16 = 42.76 pm • Time = 9 + (9 * .36) = 9 +3.24 = 12.34 months

  14. Try another example • Go through the assessment of 15 parameters for the effort adjustment factor, B. • You may have some concerns : • Are we interpreting each parameter the same way • Do we have a consistent way to assess the range of values for each of the parameters • -How good is my size (loc) estimate?

  15. COCOMO II • Effort performed at USC with many industrial corporations participating • Has a database of over 80 some projects • “Early” estimate, preferred to use Function Point instead of LOC for size; “later” estimate may use LOC for size. (loc is harder to estimate without some experience) • Coefficient B based on 15 parameters for early estimate is “rolled” up to 7 parameters, and for late estimates use 17 parameters. • Scaling factor for process has 6 categories ranging in value from .00 to .05, in increments of .01

  16. Function Point • A non-LOC based estimator • Often used to assess software “size” and “complexity” • Started by Albrecht of IBM in late 1970’s

  17. Function Pointan estimation of “size” • LOC as an estimate of “size” has many drawbacks but still used because of physical analogy: • Different programming languages has different loc meaning • Measures source code which is not available until implementation phase; it so hard to estimate during early phases of project

  18. FP Utility • Where is FP used? • Comparing software in a “normalized fashion” independent of op. system, languages, etc. • Benchmarking and “Projection” based on “size”: • size -> effort or cost • size -> development schedule • size -> defect rate • Outsourcing Negotiation

  19. Function Point • Provides you a way to estimate the size* of the project based on estimating (items from requirements & high level design): • Inputs • Outputs • Inquiries • Files • Interfaces • After getting the size, then --- still need to have an estimate on productivityand other factors to get effort in person-months: • productivity in: function-point/person-month • ** *Divide the estimated total project function points by the productivity to get an estimate of person-month or person-days needed.*** Functional/Transaction related Data related

  20. Function Point (FP) Computation • Composed of 5 “Primary Factors” • Inputting items (external input items from user or another application) • Outputting items (external outputs such as reports, messages, screens – not each data item) • Inquiry (a query that results in a response of one or more data) • Master and logical files (internal file or data structure or data table) • External interfaces (data or sets of data sent to external devices, applications, etc.) • And a “complexity level index” matrix : Simple Average Complex 3 4 6 Input 5 7 Output 4 3 Inquiry 4 6 Logical files 7 10 15 Interface 7 5 10

  21. Function Point Computation (cont.) • Initial Function Point : • ∑ (# of Primary Factor (i) x Complexity Level Index for i) • There are 14 more “Degree of Influences” ( 0 to 5 scale) : • data communications • distributed data processing • performance criteria • heavy hardware utilization • high transaction rate • online data entry • end user efficiency • on-line update • complex computation • reusability • ease of installation • ease of operation • portability • maintainability

  22. Function Point Computation (cont.) • Define Technical Complexity Factor (TCF): • TCF = .65 + (.01 x DI ) • where DI = ∑ ( influence factor values) • So note that .65 < TCF < 1.35 Function Point (FP) = Initial FP x TCF

  23. What’s one Function Point? • Do you have any experience in converting say ----- 35 function points to effort in person months? • Is there any standard conversion factor that you may use? • In IBM, during 90s, about 20 function points to 1 person month of effort (this wasback in late 1990’s --- may be more productive now).