1. Software Sizing and Costing
Anandi Hira
CS 510, Fall 2018

2. COCOMO Effort Formulation
# of cost drivers
Effort (person-months) = A (Size)E P EMi
i=1
Where:
A is a constant derived from historical project data (currently A = 2.94 in COCOMOII.2000)
Size is in KSLOC (thousand source lines of code), used since 1960s
E is an exponent for the diseconomy of scale dependent on five additive scale factors according to b = *SSFi, where SFi is a weighting factor for ith scale factor
EMi is the effort multiplier for the ith cost driver. The geometric product results in an overall effort adjustment factor to the nominal effort.
Agenda at this point - quick review of COCOMO, and each of the models I am going to bring up (IFPUG FPs, SNAP, CFPs, UCPs, SPs)
Fall 2018
©USC-CSSE

3. Software Estimation Accuracy4x 2x
Relative Size Range x
0.5x
SLOC
0.25x
Feasibility
Plans/Rqts.
Design/Architecture
Develop and Test
Need Estimates Here
Phases and Milestones
Fall 2018
©USC-CSSE

4. SLOC Pros and Cons Pros Cons Low-Level representation of software size
Seems objective
High correlation with effort
Easy to calculate at end of project (automate)
Lots of historical data available
Language-dependent
Difficult to impossible to estimate early in lifecycle
Different code counting standards/practices
Fall 2018
©USC-CSSE

5. IFPUG Function Points (FPs) (1979)EI
EIF EO EI EO EQ
EI – External Input
EO – Ext. Output
EQ – Ext. Queries
ILF – Internal Logical File
EIF – External Interface File
DET – Data Element Types
RET – Record Element Types EQ
ILF EI EO EQ
Fall 2018
©USC-CSSE

6. Software Estimation Accuracy4x 2x
Relative Size Range x
0.5x
IFPUG FPs
0.25x
Feasibility
Plans/Rqts.
Design/Architecture
Develop and Test
Need Estimates Here
Phases and Milestones
Fall 2017
©USC-CSSE

7. IFPUG Function Points Pros and Cons
Easy to calculate towards beginning to mid-lifecycle
Language independent
Objective – everyone should get same values
Decent amount of historical data available
Difficult to calculate at end of project
Difficult to automate calculation
Requires manual effort to calculate/estimate
Lacks low-level of granularity
Not applicable to all types of software
Metric not intuitive/easy to understand and calculate
Fall 2018
©USC-CSSE

8. Use Case – Diagram (1986) Withdraw Cash Transfer Funds Deposit Funds
Bank Customer
Deposit Funds
Bank
Refill Machine
Maintenance Person
Fall 2018
©USC-CSSE

9. Use Case – Written Brief Description
Bank Customer uses the ATM to withdraw money.
Actors
Bank Customer; Bank
Preconditions
There is an active network connection to the bank.
The ATM has cash available
Basic Flow
Bank Customer inserts ATM/Debit card
Validate user
ATM displays and prompts for account
Bank Customer selects account
ATM displays alternatives
Bank Customer selects withdraw option
ATM prompts for amount
Bank Customer enters an amount
ATM sends info to Bank as transaction
Fall 2018
©USC-CSSE

10. Use Case – Written Cntd. Basic Flow Money is dispensed
ATM/Debit card is returned
Receipt is printed
Alternative Flows
2a. If user is not validated, then return error
8a. If Bank Customer enters an amount that cannot be created with the type of cash in the ATM machine, display a message that amount must be in multiple of 20. Ask Bank Customer to re-enter amount.
8b. If Bank Customer enters an amount that exceeds the withdrawal limit, display warning message and ask Bank Customer to re-enter amount.
8c. If Bank Customer enters an amount that exceeds the amount available in account, return warning message and ask Customer to re-enter. …
Fall 2018
©USC-CSSE

11. Use Case Points (1993) Actor Complexity Use Case Complexity
Brief Description
Actors
Preconditions
Basic Flow
Alternative Flows
Actor Complexity
Use Case Complexity
Fall 2018
©USC-CSSE

12. Software Estimation Accuracy4x 2x
Relative Size Range x
0.5x
Use Case Points
0.25x
Feasibility
Plans/Rqts.
Design/Architecture
Develop and Test
Need Estimates Here
Phases and Milestones
Fall 2017
©USC-CSSE

13. Use Case Points Pros and Cons
Easy to calculate towards beginning to mid-lifecycle
Language independent
Objective – everyone should get same values
Uses lifecycle deliverable – requirements gathering
Automation tools exist
Difficult to calculate at end of project
Written Use Cases are tedious to write
Lacks low-level of granularity
Metric definition not based on or validated with real data
Fall 2018
©USC-CSSE

14. COSMIC Function Points (1999)
Fall 2018
©USC-CSSE

15. Software Estimation Accuracy4x 2x
Relative Size Range x
0.5x
COSMIC Methods
0.25x
Feasibility
Plans/Rqts.
Design/Architecture
Develop and Test
Need Estimates Here
Phases and Milestones
Fall 2017
©USC-CSSE

16. COSMIC Function Points Pros and Cons
Easy to calculate towards beginning to mid-lifecycle
Language independent
Objective – everyone should get same values
Decent amount of historical data available – but less than IFPUG Function Points
Difficult to calculate at end of project
Difficult to automate calculation
Requires manual effort to calculate/estimate
Fall 2018
©USC-CSSE

17. Agile Methodology (2001)
Fall 2018
©USC-CSSE

18. User Stories Structure Example
As a <Type of User>, I want <To Perform Some Task>, So that <I can achieve some Goal / Benefit / Value>
As a Customer, I want to withdraw cash from an ATM, So that I don’t have to wait in line at the Bank
Fall 2018
©USC-CSSE

19. Story Points (2004) Planning Poker Development Team
Planning Poker Cards
Fibonacci Series (1, 2, 3, 5, 8, 13, 21, …)
Estimate Size (not effort)
Fall 2018
©USC-CSSE

20. Software Estimation Accuracy4x 2x
Relative Size Range x
0.5x
Story Points
0.25x
Feasibility
Plans/Rqts.
Design/Architecture
Develop and Test
Need Estimates Here
Phases and Milestones
Fall 2018
©USC-CSSE

21. Story Points Pros and Cons
Easy to calculate towards beginning of lifecycle
Language independent
Uses lifecycle deliverable – requirements gathering
Involve team to estimate size – opportunity to understand requirements
Not objective – varies across teams
Lacks low-level of granularity
Not designed to estimate effort
Low correlation with effort
Fall 2018
©USC-CSSE

22. Software Estimation Accuracy4x 2x
Relative Size Range x
IFPUG & COSMIC Methods
0.5x
Use Case Points
Story Points
SLOC
0.25x
Feasibility
Plans/Rqts.
Design/Architecture
Develop and Test
Need Estimates Here
Phases and Milestones
Fall 2018
©USC-CSSE

23. How To Calculate Sizes IFPUG Function Points: http://www.ifpug.org/
Requires membership to get access to recent counting manual, but can get older version
Use Case Points:
COSMIC Function Points:
Story Points:
Fall 2018
©USC-CSSE