Software EffortEstimation and Risk Project Planning Activities Software Scope and Feasibility Resources Software Project Estimation Decomposition Techniques Empirical Estimation Models
- 2. Outline Estimation Introduction Software EffortEstimation and Risk Project Planning Activities Software Scope and Feasibility Resources Software Project Estimation Decomposition Techniques Empirical Estimation Models
- 3. Introduction Software Project Management begins with 'Project Planning’ activities which include: Estimation Scheduling Risk Analysis Quality Management Planning Change Management Planning
- 4. What is Estimation? Estimation is to determine how much… Money/cost, efforts, resources and time will be required to build a specific software based system or product.
- 5. Who does Estimation? Estimation is done by software project managers using information solicited from Stakeholders, Software engineers and Software metrics data from past projects.
- 6. Estimation Steps – Summary Description of product scope. Decomposition of problem into set of smaller problems. Each sub problem is estimated using historical data, software metrics and experience (from past projects) as guides. Problem complexity and risks are considered before final estimate is made.
- 7. Estimation and Risk Estimation carries inherent risk & risk leads to uncertainty. Estimation risk is measured by the degree of uncertainty in the quantitative estimates established for resources, cost, and schedule. Availability of comprehensive historical information and software metrics (from past projects) helps establish better estimates and hence reduces risk factors.
- 8. Estimation and Risk (Contd.) If project scope is poorly understood or requirements are subject to change then uncertainty and estimation risk become dangerously high. Thus variability in software requirements means instability in cost and schedule. However, a project manager should not become obsessive about estimation as modern software engineering approaches are iterative in nature hence making it possible to revise estimates.
- 9. Software Project Planning Process Software project planning provides a framework that enables the manager to make reasonable estimates of resources, cost and schedule. Although there is inherent uncertainty, the team embarks on a project plan. But, this plan must be adapted and updated as the project progresses.
- 10. Software Project Planning Activities Establish project scope Determine feasibility Analyze risks Define resources Estimate cost and effort Develop project schedule Lets discuss these in detail …
- 11. Software Scope It is defined in one of the following ways: A narrative description developed after communication with all stakeholders A set of use-cases developed by end-user It describes functions & features to be delivered to end-user Input and output data “content” presented to users as they use the software Performance considerations (processing and response time, etc) Constraints (limits placed on software by external hardware, available memory, or existing systems), interfaces and reliability that bound the system
- 12. Software Feasibility Feasibility check is conducted after scope identification. It addresses questions like Can we build software to meet this scope? Is the project feasible? These questions are very crucial but often overlooked either by software engineers or by the impatient customers and managers.
- 13. Software Feasibility (Contd.) Putnam and Myers address feasibility in four dimensions Technology Is the project technically feasible? Is it within state of the art? Can defects be reduced as needed? Finance Is it financially feasible? Can the development be completed at a cost that the software organization, the client or the market can afford Time Will the project’s time-to-market beat the competition? Resources Does the organization have enough resources needed to succeed?
- 14. Resources After scope and feasibility, next comes estimation of resources. Three major categories of resources are: People/Human resources Reusable software components Development environment (s/w & h/w tools) Each resource has 4 characteristics Description of resource Statement of availability Time when resource will be required Duration of time when resource will be applied
- 15. 1.Human resources This estimation involves Selecting Skills (required to complete development) Specifying organizational positions (manager, senior s/w engr, ..) and specialty Determining number of people based on development effort For small projects, single person can do all s/w engg tasks For large projects, more number of people involved which may be geographically distributed. So, location of resource also specified No. of people can be determined after estimating development effort (e.g., person-months)
- 16. 2. Reusable Software Resources CBSE emphasizes the creation and reuse of software building blocks (components) 4 categories of software components Off-the-shelf components Ready-to-use existing software acquired from third party (COTS) or from (internal) past projects Full-experience components Existing specifications, designs, code, test data from past projects similar to software to be developed (for current project). May require little modifications
- 17. 2. Reusable Software Resources Partial experience component Existing specifications, designs, code, test data from past projects related to software to be developed (for current project) but will require substantial modifications New components Software components that must be built for current project
- 18. 3. (Development) Environment resources Software Engineering Environment (SEE) includes hardware and software support for a software project Hardware and software elements availability and time window must be specified
- 19. Software Project Estimation Options for cost and effort estimates: Delay estimation until late in project Not a practical approach Base estimation on similar past projects Reasonable approach but not always successful Use simple decomposition techniques to generate estimates Divide and conquer approach. Divide project into major activities/functions and make estimates Use some empirical model for estimation Complements decomposition techniques Which option is better? Each approach can be used as a cross-check for the other
- 20. Decomposition Techniques Decomposition can be performed in two aspects Decomposition of problem Decomposition of process Estimation uses one or both forms of decompositions. But before this, software size must be estimated.
- 21. Software Sizing Proper estimation of software size and mapping of size estimate to human effort, calendar time and cost are important things which contribute to accuracy of overall software project estimation. In project planning, size refers to a quantifiable outcome. Direct approach – size is measured as LOC Indirect approach – size is measured as function-points
- 22. Software Sizing (Contd.) Putnam and Myers suggested 4 different approaches for sizing problem Fuzzy logic sizing Function point sizing Standard component sizing Change sizing
- 23. Other types of estimations… Problem based estimation (LOC- based and FP-based) Process-based estimation Use-case based estimation
- 24. References Today’s lecture contents were taken from chapter 23 – “Software Engineering, A Practitioner's Approach” by Roger Pressman