第六講_軟件工作量估計

1、.,軟件工作量估計,主講人：王輝 2014-03-04,.,復習：項目計劃的三個關(guān)鍵步驟,任務分解（WBS） 工作量估計 資源、進度安排,.,復習：標識項目的活動-WBS,.,復習：標識項目的活動-混合方法,.,復習：軟件工作量的度量,源代碼行數(shù)(Source Line Of Code)：SLOC 千行代碼(Kilo Line Of Code)：KLOC 功能點(Function Point)：FP，實現(xiàn)方法無關(guān) 人月(person month)：pm，125個工時,.,復習：軟件工作量估計的方法,專家判斷 類比估計 由底向上 自頂向下 Albrecht功能點 Mark II 功能點 COSM

2、IC全功能點,.,復習：功能點的步驟,確定系統(tǒng)中的功能（構(gòu)件）的類型 確定每種功能的權(quán)重 加權(quán)求和為系統(tǒng)的功能點,.,復習:Albrecht功能類型,External input (EI) types 外部輸入類型 input transactions which update internal computer files. External output (EO) types 外部輸出類型 transactions which extract and display data from internal computer files. Generally involves creating

3、 reports External inquiry (EQ) types 外部查詢類型 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.,.,復習:Albrecht功能類型,Logical interface file (LIF) types 內(nèi)部邏輯文件類型 equates rough

4、ly to a datastore in systems analysis terms. Created and accessed by the target system. External interface file types (EIF) 外部接口文件類型 where data is retrieved from a datastore which is actually maintained by a different application.,.,復習:Albrecht功能的權(quán),.,課堂測試,研發(fā)一個信息系統(tǒng)，該系統(tǒng)的外部輸入類型有兩個，復雜度分別為低和高；復雜度為高的外部輸出類

5、型1個；復雜度為中的內(nèi)部邏輯文件類型2個；復雜度為低的外部接口文件類型3個。請用Albrecht方法估計其工作量。,3 + 6 + 7 + 10 * 2 + 5 * 3 = 51,.,復習：Mark II功能點,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,.,復習：COSMIC全功能點,The following a

6、re counted: Entries 進入: movement of data into software component from a higher layer or a peer component Exits 退出: movements of data out Reads 讀: data movement from persistent storage Writes 寫: data movement to persistent storage Each counts as 1 COSMIC functional size unit (Cfsu),.,軟件工作量估計的具體方法,3.1

7、 專家判斷 3.2 類比估計 3.3 由底向上 3.4 自頂向下 3.5 Albrecht功能點 3.6 Mark II 功能點 3.7 COSMIC全功能點 3.8 COCOMO：參數(shù)化的生產(chǎn)率模型,.,3.8 COCOMO,Boehm的COCOMO 81 (COnstructive COst MOdel, 構(gòu)造型成本模型) COCOMO II是其最新的發(fā)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，千行源代碼 c, k取決于系統(tǒng)的類型：有機式(organic)，半相連式(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) 開發(fā)靈活性. Degree of flexibility that exists when implementing the project Architecture/risk resolution (RES

11、L) 構(gòu)架/風險解決方案. Degree of uncertainty about requirements Team cohesion (TEAM) 團隊凝聚力. Process maturity (PMAT) 過程成熟度 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 (產(chǎn)品的可靠性和復雜度) RUSE Reuse required (需要的可用性) PDIF Platform difficulty (平臺難度) PERS Personnel capability (人員的能力) PREX Personnel Experience (人員的經(jīng)驗) FCIL Facilities available (設(shè)施的可用性) SCED Schedule pressure (進度壓力),.,Effort Multiplier,.,Example -continued,RCPX (產(chǎn)品的可靠性和復雜度)very high1.91 PDIF (平臺難度) very high1.81 PERS (人員的能力) extra high0.50 PREX (人員的經(jīng)驗) nominal1.00 All other factors are nominal Say estimate is 35.8135 person months With effort multipliers this b