مقدمة في هندسة البرمجيات - التخطيط والتقدير

Introduction to Software Engineering - Planning, Cost Estimation, and Project Scheduling

• Course: Introduction to Software Engineering (ITGS-213)
• Topic: Planning, Cost Estimation, and Project Scheduling
• Software Development Cycle (SDLC): A well-defined, structured, and measurable approach to software development and maintenance.
• SDLC Stages: Planning, Analysis, Design, Implementation, Testing & Integration, Maintenance.
• Project Management: A critical aspect of software engineering. Poor management leads to project failure (missed deadlines, exceeding budget, failing to meet requirements).
• Software Project Management Activities: Project planning, defining software scope, cost estimation (various perspectives), task scheduling, resource management.

Planning a Software Project

• Activities: Defining project goals, feasibility study, identifying project requirements (hardware, software, human resources), outlining project boundaries and potential risks, estimating project duration, estimating project cost.
• Cost and Time Estimation: Crucial and challenging parts of planning. Inaccurate estimations can lead to system failure and significant financial loss.
• Scheduling is Important: Tied to cost estimation, impacts project success, and requires methods to estimate time for each project task.
• Factors Affecting Cost Estimation: Software complexity, software size, technology used, programmer performance.

Cost Estimation

• Initial and Detailed Estimations: Initial evaluations for feasibility assessment; detailed estimations for project plans.
• Factors Influencing Cost:
  • Complexity of Software: Higher complexity leads to higher costs.
  • Size of Software: Larger software projects tend to be more expensive.
  • Technology Used: Modern technologies often have a relationship inverse to cost (i.e. less expensive modern technologies) compared to older technologies.
  • Programmer Performance: A skilled programmer can reduce project cost.

Challenges in Cost Estimation

• Lack of Similar Past Projects: Estimating costs in projects without precedent.
• Increased Project Complexity: Project complexity increases the estimation difficulty.
• Inaccurate Estimation Tools & Methods: Tools and methods may not precisely predict costs.

Methods for Cost Estimation

• Expert Judgement: Experts use experience to estimate project cost.
  • Pros: Can be accurate if experts have comparable project experience.
  • Cons: Can be inaccurate if not enough relevant project experience.
• Estimation by Analogy (Comparison): Estimating costs by comparing to similar projects
  • Pros: Can be precise if data from the old project matches.
  • Cons: Is impossible if a comparable project doesn't exist.
• Group Consensus/Delphi method: Aggregating expert opinions.
  • Steps: Defining system and providing preliminary cost estimate models for specialists. Specialists avoid sharing perspectives with each other; the coordinator collects and reviews estimations, addressing any needed information or large variances in cost estimates; repeating this until a consensus is reached without any in-person discussions..

Software Project Scheduling

• Scheduling Tools and Methods: Similar for software, construction and industrial projects; leveraging previous project schedules where possible; dividing work into components, accounting for parallel and sequential dependencies.
• Project Delays: Factors leading to possible project delays include illnesses in the staff, equipment failures, delayed equipment/training.
• Important considerations:
  • Parallel and sequential work tasks, minimal workforce, unexpected staff departures, documentation(requirements and design) times are often longer than actual coding time.
• Time Unit Considerations: Days are common, sometime using hours to account for differing workplace schedules.

Scheduling Tools

• Gantt Charts: Graphical planning tool, using the horizontal axis for execution time and vertical axis for activity names.
• Critical Path Method (CPM): Network-based planning; identifies activities & estimated time for each; calculates longest path (earliest event time) from start to end; identifies longest path to indicate project completion time.
• PERT (Project Evaluation and Review Technique): More time-conscious approach for uncertain estimates.

Critical Path Method (CPM) Steps

• Earliest Event Time (EEj): Earliest possible starting time for an activity, occurring after completion of all preceding activities.

• Latest Event Time (LEj): Latest possible time for an event (activity) without affecting the critical path. Typically equal to earliest time for the activity.

• Slack Time(S): Difference between earliest and latest time for tasks; tasks with zero slack are critical path.