第六讲 软件工作量估计 cont.ppt

第六讲_软件工作量估计_cont
第一页，共27页。
复****项目计划的三个关键步骤
任务分解（WBS）
工作量估计
资源、进度安排
第二页，共27页。
复****标识项目的活动-WBS
第三页，共27页。
f data into software component from a higher layer or a peer component
Exits 退出: movements of data out
Reads 读: data movement from persistent storage
Writes 写: data movement to persistent storage
Each counts as 1 ‘COSMIC functional size unit’ (Cfsu)
第十三页，共27页。
软件工作量估计的具体方法
专家判断
类比估计
由底向上
自顶向下
Albrecht功能点
Mark II 功能点
COSMIC全功能点
COCOMO：参数化的生产率模型
第十四页，共27页。
COCOMO
Boehm的COCOMO 81 (COnstructive COst MOdel, 构造型成本模型)
COCOMO II是其最新的发展
第十五页，共27页。
COCOMO 81
Basic model
effort = c x sizek
Effort 是按人月(pm)度量的
Size 是按kdsi度量的，千行源代码
c, k取决于系统的类型：有机式(organic)，半相连式(semi-detached)，嵌入式(embedded)
第十六页，共27页。
The COCOMO 81 Constants
System type
c
k
Organic (broadly, information systems)


Semi-detached


Embedded (broadly, real-time)


k exponentiation – ‘to the power of…’
adds disproportionately more effort to the larger projects
takes account of bigger management overheads
第十七页，共27页。
COCOMO II
An updated version of COCOMO 81:
There are different COCOMO II models for estimating at the ‘early design’ stage and the ‘post architecture’ stage when the final system is implemented. We’ll look specifically at the first.
The core model is:
pm = A(size)(sf) ×(em1) ×(em2) ×(em3)….
where pm = person months, A is , size is number of thousands of lines of code (kdsi, kloc), sf is the scale factor, and em is an effort multiplier
第十八页，共27页。
COCOMO II: scale factor(sf)
sf = B() + ×
Precedentedness (PREC) 有先例. Degree to which there are past examples that can be consulted
Development flexibility (FLEX) 开发灵活性. Degree of flexibility that exists when implementing the project
Architecture/risk resolution (RESL) 构架/风险解决方案. Degree of uncertainty about requirements
Team cohesion (TEAM) 团队凝聚力.
Process maturity (PMAT) 过程成熟度 Could be assessed by CMMI