Software Cost Estimation - Lecture Notes | CS 389, Exams of Software Engineering

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Software cost estimation

l Predicting the resources

required for a software

development process

Objectives

l To introduce the fundamentals of software costing and pricing l To describe three metrics for software productivity assessment l To explain why different techniques should be used for software estimation l To describe the COCOMO 2 algorithmic cost estimation model

Fundamental estimation questions

l How much effort is required to complete an activity? l How much calendar time is needed to complete an activity? l What is the total cost of an activity? l Project estimation and scheduling and interleaved management activities

Software cost components

l Hardware and software costs l Travel and training costs l Effort costs (the dominant factor in most projects)

• salaries of engineers involved in the project
• Social and insurance costs l Effort costs must take overheads into account
• costs of building, heating, lighting
• costs of networking and communications
• costs of shared facilities (e.g library, staff restaurant, etc.)

Software pricing factors

Factor Description Market opportunity A development organisation may quote a low price because it wishes to move into a new segment of thesoftware market. Accepting a low profit on one project may give the opportunity of more profit later.The experience gained may allow new products to be developed. Cost estimate uncertainty If an organisation is unsure of its cost estimate, itmay increase its price by some contingency over and above its normal profit. Contractual terms A customer may be willing to allow the developer to retain ownership of the source code and reuse it inother projects. The price charged may then be less than if the software source code is handed over to thecustomer. Requirements volatility If the requirements are likely to change, an organisation may lower its price to win a contract.After the contract is awarded, high prices may be charged for changes to the requirements. Financial health Developers in financial difficulty may lower their price to gain a contract. It is better to make a small profit or break even than to go out of business.

l A measure of the rate at which individual engineers involved in software development produce software and associated documentation l Not quality-oriented although quality assurance is a factor in productivity assessment l Essentially, we want to measure useful functionality produced per time unit

Programmer productivity

l Estimating the size of the measure l Estimating the total number of programmer months which have elapsed l Estimating contractor productivity (e.g. documentation team) and incorporating this estimate in overall estimate

Measurement problems

l What's a line of code?

• The measure was first proposed when programs were typed on cards with one line per card
• How does this correspond to statements as in Java which can span several lines or where there can be several statements on one line l What programs should be counted as part of the system? l Assumes linear relationship between system size and volume of documentation

Lines of code

High and low level languages

Analysis Design C oding Validation

Low-level language

Analysis Design Coding Validation

High-level language

System development times

Analysis Design Coding Testing Documentation Assembly code High-level language

3 weeks 3 weeks

5 weeks 5 weeks

8 weeks 8 weeks

10 weeks 6 weeks

2 weeks 2 weeks Size Effort Productivity Assembly code High-level language

5000 lines 1500 lines

28 weeks 20 weeks

714 lines/month 300 lines/month

Function points

l Function point count modified by complexity of the project l FPs can be used to estimate LOC depending on the average number of LOC per FP for a given language

• LOC = AVC * number of function points
• AVC is a language-dependent factor varying from 200-300 for assemble language to 2-40 for a 4GL l FPs are very subjective. They depend on the estimator.
• Automatic function-point counting is impossible

Object points

l Object points are an alternative function-related measure to function points when 4Gls or similar languages are used for development l Object points are NOT the same as object classes l The number of object points in a program is a weighted estimate of

• The number of separate screens that are displayed
• The number of reports that are produced by the system
• The number of 3GL modules that must be developed to supplement the 4GL code

l Real-time embedded systems, 40- LOC/P-month l Systems programs , 150-400 LOC/P-month l Commercial applications, 200- LOC/P-month l In object points, productivity has been measured between 4 and 50 object points/month depending on tool support and developer capability

Productivity estimates

Factors affecting productivity

Factor Description Application domain experience

Knowledge of the application domain is essential for effective software development. Engineers whoalready understand a domain are likely to be the most productive. Process quality The development process used can have a significant effect on productivity. This is covered in Chapter 31. Project size The larger a project, the more time required for team communications. Less time is available for development so individual productivity is reduced. Technology support Good support technology such as CASE tools, supportive configuration management systems, etc. can improve productivity. Working environment As discussed in Chapter 28, a quiet working environment with private work areas contributes to improved productivity.