Chapter 5 Estimate Influences

Transcription

1 Dilbert Scott Adams

2 Dilbert Scott Adams

3 Chapter 5 Estimate Influences How much is ? ENGINEER: It s 141. Short and sweet. MATHEMATICIAN: = by the commutative law of addition. True, but not very helpful. ACCOUNTANT: Normally it s 141, but what are you going to use it for? Barry Boehm & Richard Farley Influences on effort, cost and schedule of software projects: Project size is the most significant The kind of software is second Personnel factors are a close third Note. Language & environment are not first tier influences on the outcome, but they are on the estimate.

4 Why use Lines of Code (LOC)? A system requiring 1,000,000 LOC needs much more effort that a system consisting of 100,000 LOC How is this used often not at all Cost, effort, schedule: Estimated without knowing how big the software will be Not adjusted when the size is increased (change requests) Why LOC? Many languages are not as LOC oriented as older languages Req ts, design and testing don t produce LOC Coming in Chapter 18

5 Project Size (Fig. 5-1) 600, , ,000 Effort (staff months) 300, , , ,000 1,500 2,000 2,500 3,000 Project Size (LOC)

6 Diseconomies of Scale Larger projects require coordination between larger groups of people Meaning more communication! N ( N 1 ) / 2

7 Diseconomies of Scale But also Project conditions degrade productivity 6,000 5,000 4,000 Effort (staff months) 3,000 2,000 1, , , , ,000 1,000,000 Project Size (LOC)

8 Project Size & Productivity (Table 7-1) General relationship between Size & Productivity Numbers valid just for comparison purposes Depicts general trend: Small 10K project can be 2 to 3 times greater than large projects Small 10K project can be 5 to 10 more productive than large projects Project Size (LOC) Lines of Code per Staff Year 10K 2,000-25,000 (3,200) 100K 1,000-20,000 (2,600) 1M ,000 (2,000) 10M 300-5,000 (1,600) Cocomo II Nominal in Parentheses)

9 Bad news Large variation in sizes of projects prohibits using some simple effort ratio based on previous experience. Book example: Previous project: 100,000 LOC and 170 staff months Productivity Standard: 100, = 588 LOC / staff month A different size project would not have 588 LOC / staff month No technique to account for the difference in the size of projects.

10 Good news! Majority of projects in most organizatins are similar in size Yes, use a simple effort ratio. But Use it only for a small range of sizes Difference only within a factor of 3 from smallest to largest Estimate in the mid range variation roughly only 10% Tip Size is the number one influence on your estimate

11 Different kinds of SW apps Next biggest influence on your estimate! (Table 5-2) PROJECT SIZE Kind of SW 10,000 LOC 100,000 LOC 250,000 LOC Avionics 100-1, Business Systems , , ,000 Command & Control 200-3,000 50, Embedded Systems 100-2,000 30, Internet Systems (public) , , ,500 Intranet Systems (private) 1,500-18, , ,000 Microcode Process Control 500-5, , Real-Time 100-1, Scientific 500-7, , ,000 Systems/Engineering Research Shrink wrap/packaged SW 400-5, , Systems SW / Drivers 200-5, , Telecommunications 200-5,

12 How to estimate: Given a specific industry 1. Use Table 5-2 difference of a factor of 10 between high and low. 2. Use an estimating model (Cocomo II with adjustments for the specific kind of software). 3. Use historical data includes factors specific to the industry (Chapter *)

13 Personnel Factors 100,000 LOC Project: Combined effect of personnel factors can swing the estimate by as much as a factor of 22 Best Nominal Worst Req'ts Analyst Capability -29% 42% Programmer Capability (General) -24% 34% Personnel Continuity (Turnover) -19% 29% Applications (Business Area) Experience -19% 22% Language & Tools Experience -16% 20% Platform Experience -15% 19% Team Cohesion -14% 11%

14 Functionality per Line of Code (LOC) If you have the choice of language, pick one that is more productive than C, Cobol or Macro Assembly Language Level Relative to C C 1 to 1 C# 1 t0 2.5 C++ 1 to 2.5 Cobol 1 to 1.5 Fortran 95 1 to 2.5 Java 1 to 2.5 Macro Assembly 2 to 1 Perl 1 to 6 Smalltalk 1 to 6 SQL 1 to 10 Visual Basic 1 to 4.5

15 Organic Cocomo Development - Modes Relatively small, simple softwre proejcts in which small teams with good application experience work to a set of flexible requirements Embedded Software project has tight software, hardware and operational constraints Semi-detached Intermediate (in size and complexity) software project in which teams with mixed experience levels must meet a mix of rigig and less than rigid requirements

16 Cocomo Model E b = as ( ) Product(cost drivers) Where: E represents effort per staff-month S is the size of the SW development in KLOC a and b are values dependent on the development mode Development Modes: Organic a = 2.4 b = 1.05 Semi-detached a = 3.0 b = 1.12 Embedded a = 3.6 b = 1.20

17 Cocomo II Adjustment Factors Table 5-4 Very Low impact Very Low Low Nominal High Influence of factor on overall estimate Very High impact = (Max value Min value) Table 5-5 Definitions for each Factor Very High Extra High Influence Applications (Business Area) Experience Database Size Developed for Reuse Extent of Documentation Required Language & Tools Experience Multisite Development Personnel Continuity (Turnover) Platform Experience Platform Volatility Product Complexity Programmer Capability (General) Required SW Reliability Req'ts Analyst Capability Storage Constraint Time Constraint Use of SW Tools

18 Cocomo II Factors (Table 5-7) Influence of each factor On the Effort estimate

19 The Model in Action Cost Drivers (see handout): Product High = = 1.43 Computer Nominal = 1.00 Personnel Low = = 1.85 Project Hign = = 0.86 Cost Drivers = = 2.28 Semi-detached project of 56 KLOC E b = as ( ) Product (cost drivers) a = 3.0 b = 1.12 S = E = 3.0 (56) 2.28 = staff months

20 5 scaling factors contributing to Diseconomies of Scale 1. Process Maturity 2. Architecture and Risk Resolution 3. Precedentedness 4. Team Cohesion 5. Development Flexibility Project Size of 100,000 LOC

21 5 scaling factors contributing to Diseconomies of Scale 1. Process Maturity 2. Architecture and Risk Resolution 3. Precedentedness 4. Team Cohesion 5. Development Flexibility Project Project Size Size of 5,000,000 of 5,000,000 LOC LOC

22 Cost Drivers V.LOW LOW NOMINAL HIGH V.HIGH EX.HIGH PRODUCT RELY DATA CPLX COMPUTER TIME STOR VIRT TURN PERSONNEL ACAP AEXP PCAP VEXP LEXP PROJECT MODP TOOL SCED

23 Questions refer to last page of handout 1. For the above cost drivers to be multiplied together the underlying assumption is that they must be independent of each other, does this sound reasonable? 2. If all cost drivers were at minimum value, what would be the product of the cost drivers? 3. If all cost drivers were at maximum value, what would be the product of the cost drivers? 4. Based on the results to the two questions above, what is the ratio between maximum and minimum possible predicted effort? 5. Does the possible range from maximum to minimum effort seem reasonable? 6. The SCED cost driver is unique in the above table - can you see, and explain, why? 7. COCOMO starts from estimate of size, subjective assessment of 15 (independent?) cost drivers (with values - on potentially a 6- point scale - based on 60+ datasets), to estimate effort. How much confidence should you have in the final estimate?