第六讲_软件工作量估计

1、.,软件工作量估计,主讲人：王辉 2014-03-04,.,复习：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,.,复习：标识项目的活动-WBS,.,复习：标识项目的活动-混合方法,.,复习：软件工作量的度量,源代码行数(Source Line Of Code)：SLOC 千行代码(Kilo Line Of Code)：KLOC 功能点(Function Point)：FP，实现方法无关 人月(person month)：pm，125个工时,.,复习：软件工作量估计的方法,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 COSM

2、IC全功能点,.,复习：功能点的步骤,确定系统中的功能（构件）的类型 确定每种功能的权重 加权求和为系统的功能点,.,复习:Albrecht功能类型,External input (EI) types 外部输入类型 input transactions which update internal computer files. External output (EO) types 外部输出类型 transactions which extract and display data from internal computer files. Generally involves creating

3、 reports External inquiry (EQ) types 外部查询类型 user initiated transactions which provide information but do not update computer files. Normally the user inputs some data that guides the system to the information the user needs.,.,复习:Albrecht功能类型,Logical interface file (LIF) types 内部逻辑文件类型 equates rough

4、ly to a datastore in systems analysis terms. Created and accessed by the target system. External interface file types (EIF) 外部接口文件类型 where data is retrieved from a datastore which is actually maintained by a different application.,.,复习:Albrecht功能的权,.,课堂测试,研发一个信息系统，该系统的外部输入类型有两个，复杂度分别为低和高；复杂度为高的外部输出类

5、型1个；复杂度为中的内部逻辑文件类型2个；复杂度为低的外部接口文件类型3个。请用Albrecht方法估计其工作量。,3 + 6 + 7 + 10 * 2 + 5 * 3 = 51,.,复习：Mark II功能点,data items input (Ni) data items output (No) entity types accessed (Ne),#entities accessed,#input items,#output items,FP count = Ni * 0.58 + Ne * 1.66 + No * 0.26,.,复习：COSMIC全功能点,The following a

6、re counted: Entries 进入: movement of 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),.,软件工作量估计的具体方法,3.1

7、 专家判断 3.2 类比估计 3.3 由底向上 3.4 自顶向下 3.5 Albrecht功能点 3.6 Mark II 功能点 3.7 COSMIC全功能点 3.8 COCOMO：参数化的生产率模型,.,3.8 COCOMO,Boehm的COCOMO 81 (COnstructive COst MOdel, 构造型成本模型) COCOMO II是其最新的发展,.,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

8、-detached)，嵌入式(embedded),.,The COCOMO 81 Constants,k exponentiation to the power of adds disproportionately more effort to the larger projects takes account of bigger management overheads,.,COCOMO II,An updated version of COCOMO 81: There are different COCOMO II models for estimating at the early de

9、sign stage and the post architecture stage when the final system is implemented. Well look specifically at the first. The core model is: pm = A(size)(sf) (em1) (em2) (em3). where pm = person months, A is 2.94, size is number of thousands of lines of code (kdsi, kloc), sf is the scale factor, and em

10、is an effort multiplier,.,COCOMO II: scale factor(sf),sf = B(0.91) + 0.01 ,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 (RES

11、L) 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,.,Scale Factors,.,Example,A software development team is developing an application which is very similar to previous ones it has developed. A very precise softwa

12、re engineering document lays down very strict requirements. PREC is very high (score 1.24). FLEX is very low (score 5.07). The good news is that these tight requirements are unlikely to change (RESL is high with a score 2.83). The team is tightly knit (TEAM has high score of 2.19), but processes are

13、 informal (so PMAT is low and scores 6.24),.,Scale Factor,sf = 0.91 + 0.01 (1.24 + 5.07 + 2.83 + 2.19 + 6.24) = 0.91 + 0.01 17.56 = 0.91 + 0.1756 = 1.0856,If system contained 10 kloc then estimate would be 2.94 x 101.0857 = 35.8135 person months,.,COCOMO II: effort multiplier (em),RCPX Product relia

14、bility and complexity (产品的可靠性和复杂度) RUSE Reuse required (需要的可用性) PDIF Platform difficulty (平台难度) PERS Personnel capability (人员的能力) PREX Personnel Experience (人员的经验) FCIL Facilities available (设施的可用性) SCED Schedule pressure (进度压力),.,Effort Multiplier,.,Example -continued,RCPX (产品的可靠性和复杂度)very high1.91 PDIF (平台难度) very high1.81 PERS (人员的能力) extra high0.50 PREX (人员的经验) nominal1.00 All other factors are nominal Say estimate is 35.8135 person months With effort multipliers this b