Page 109 - DCAP305_PRINCIPLES_OF_SOFTWARE_ENGINEERING

Unit 5: Software Project Planning

Range Estimates: Coarse-grained cost driver information in the early project stages, and Notes
increasingly fine-grained information in later stages. Not point estimates of software cost and
effort, but rather range estimates tied to the degree of definition of the estimation inputs.
5.4.4 Differences between COCOMO I and COCOMO II

The major differences between COCOMO I AND COCOMO II are:
• COCOMO’81 requires software size in KDSI as an input, but COCOMO II is based on
KSLOC (logical code). The major difference between DSI and SLOC is that a single Source
Line of Code may be several physical lines. For example, an “if-then-else” statement would
be counted as one SLOC, but might be counted as several DSI.
• COCOMO II addresses the following three phases of the spiral life cycle: applications
development, early design and post architecture.
• COCOMO’81 provides point estimates of effort and schedule, but COCOMO II provides
likely ranges of estimates that represent one standard deviation around the most likely
estimate.
• The estimation equation exponent is determined by five scale factors (instead of the three
development modes).
• Changes in cost drivers are:
○ Added cost drivers 7: DOCU, RUSE, PVOL, PLEX, LTEX, PCON, and SITE.
○ Deleted cost drivers (5): VIRT, TURN, VEXP, LEXP, and MODP.
○ Alter the retained ratings to reflect more up-do-date software practices.
• Data points in COCOMO I: 63 and COCOMO II: 161
• COCOMO II adjusts for software reuse and reengineering where automated tools are used
for translation of existing software, but COCOMO’81 made little accommodation for these
factors.

• COCOMO II accounts for requirements volatility in its estimates.
5.4.5 COCOMO II Model Definition
The COCOMO II provides three stage series of models for estimation of software projects:
Application Composition Model: This is used for earliest phases or spiral cycles (prototyping,
and any other prototyping occurring later in the life cycle).
Early Design Model: This is for next phases or spiral cycles. Involves exploration of architectural
alternatives or incremental development strategies. Level of detail consistent with level of
information available and the general level of estimation accuracy needed at this stage.
Post-Architecture Model: Once the project is ready to develop and sustain a fielded system it
should have a life-cycle architecture, which provides more accurate information on cost driver
inputs, and enables more accurate cost estimates.
Self Assessment Questions

1. Burenius and Lindstedt ......................... as the machines of the project.
(a) Setting up Milestones (b) Identify activities

(c) Allocate resources (d) Create a time-schedule
2. The ............................ model computes effort as a function of program size and a set of cost
drivers weighted according to each phase of the software lifecycle.
(a) Intermediate COCOMO (b) Advanced COCOMO
(c) detailed COCOMO (d) None of these

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