【正文】 s environment, such as the operating system and hardware, changes over time ? Required turnaround time—The measurement of time required for user feedback 3. Product ? Required software reliability—The degree to which software errors can be tolerated. The range for poor reliability can be from slight inconvenience to risk to human life. ? Size of application database—The ratio of the data storage to the program size ? Complexity of product—The degree of plexity in the application functions. Simple functions have simple expressions in the putational operations, very little nesting in the control operations, and data management operations that consist of simple arrays in main memory. Complex functions have highly nested control operations, difficult mathematical putations, dynamic data relationships in the data storage, and microcoding for devicedependent operations 4. Project ? Use of software tools—The richness in features of the tools being used for development. Tools can be very basic and require additional manual involvement or quite prehensive with automated design, documentation, and coding ponents. ? Application of software engineering methods—The degree of mitment of the staff to using software engineering methods ? Required development schedule—The significance of the project delivery date, a high rating means that early delivery is very desirable or needed. ? You will need to rate each of these cost drivers on a scale from very low to nominal to very high. ? Each cost driver influences the COCOMO I estimate but not in the same way. ? For example, if you rated software engineer capability very high the estimate would be reduced, which makes sense: If the team of software engineers is very capable they can plete the project in a shorter period of time. ? Once you have used the function point method and the COCOMOI model to estimate product size, effort, and schedule length, you have some idea of what kind of project you are faced with. ? If your estimates far exceed the schedule you were given, now is the time to sound the alarm. ? Accepting an impossible schedule dooms you and the team to failure. ? Even if you can39。s aptitude ? Software engineer capability—The percentile ranking of the programmer39。 Schedule length = (Effort)035 3. Embedded Effort = (KSLOC)。s general operations, such as startup, backup, recovery, and shutdown. ? Multiple sites—The number of installations of the application across diverse anizations or sites. ? Facilitate change—The appraisal (assessment) of the application in terms of how easily it acmodates user modifications, such as providing a flexible query facility or functions for setting and maintaining user defined parameters. ? Once you have the function points and plexity factors, choose your development language from the list of available languages to determine the SLOC estimate. ? COSMOS allows you to adjust these counts for your particular anization, which you should consider during project assessment. ? The function point method is not perfect, Two people may arrive at different estimates. ? In practice, though, this can be a good thing because each person may have considered factors the other did not, or put different emphases on different factors. ? An excellent way to get more accurate estimates is to have two or more people count and adjust function points separately, then meet and resolve the differences to form a single estimate. COCOMO I ? The COCOMO I model requires as input a product SLOC estimate. Using this estimate, COCOMO I produces an estimate of the effort and schedule length for a project. ? Much like the function point method, the more sophisticated Intermediate COCOMO I model uses additional inputs unique to your project to adjust this basic estimate. ? COCOMO I actually contains models for three types of projects: ? 1. OrganicRelatively small projects from stable, familiar, fiving, and relatively unconstrained environments ? 2. Semidetachedintermediatesized projects from less stable, less familiar, less fiving environments with some rigid constraints ? 3. EmbeddedAmbitious intermediate or large projects from unfamiliar,unfiving, and tightly constrained environments ? You need to classify your project into one of these types in order to use the correct estimation formula. ? The COCOMO I model estimates effort and schedule for each of these types of projects with slightly different formulas. The formulas (where KSLOC is one thousand SLOC) are: 1. Organic Effort = (KSLOC)。 it only means you need to update your schedule. ? Iterative and staged development processes specifically assume schedules are incorrect and attempt to solve this problem by scheduling only a limited distance into the future. ? Your first task is size estimation. How big is this project? From this number, estimate how long it will take to plete the project. ? This book introduces the function point method for size estimation and the COCOMO model for effort and schedule estimation. ? Many if not most software projects have immovable milestones in their schedules before the project is even launched. ? Immovable milestones force you to estimate how much of the project your team