Slide 1 : Introduction to Software Engineering - Priya Jain
Software Engineering : Software Engineering Software Engineering is the science and art of
building significant software systems that are:
1) on time
2) on budget
3) with acceptable performance
4) with correct operation.
Software Engineering : Software Engineering The economies of all developed nations are dependent on software.
More and more systems are software controlled.
Software engineering is concerned with theories, methods and tools for professional software development.
Software engineering expenditure represents a significant fraction of the GNP of developed countries.
Software Costs : Software costs often dominate system costs. The costs of software on a PC are often greater than the hardware cost.
Software costs more to maintain than it does to develop.
Software engineering is concerned with cost-effective software development. Software Costs
Software Products : Software Products Generic products:
Stand-alone systems which are produced by a development organization and sold on the open market to any customer.
Customized products:
Systems which are commissioned by a specific customer and developed specially by some contractor.
Software Product Attributes : Software Product Attributes Maintainability
Dependability
Efficiency
Usability
Importance of Product Characteristics : Importance of Product Characteristics The relative importance of these characteristics depends on the product and the environment in which it is to be used.
In some cases, some attributes may dominate
In safety-critical real-time systems, key attributes may be dependability and efficiency.
Costs tend to rise exponentially if very high levels of any one attribute are required.
Efficiency Costs : Efficiency Costs
The Software Process : The Software Process Structured set of activities required to develop a software system
Specification
Design
Validation
Evolution
Activities vary depending on the organization and the type of system being developed.
Must be explicitly modeled if it is to be managed.
Engineering Process Model : Engineering Process Model Specification: Set out the requirements and constraints on the system.
Design : Produce a model of the system.
Manufacture : Build the system.
Test: Check the system meets the required specifications.
Install: Deliver the system to the customer and ensure it is operational.
Maintain: Repair faults in the system as they are discovered.
Software Engineering is Different : Software Engineering is Different Normally, specifications are incomplete.
Very blurred distinction between specification, design and manufacture.
No physical realization of the system for testing.
Software does not wear out - maintenance does not mean component replacement.
Generic Software Process Models : Generic Software Process Models Waterfall
Separate and distinct phases of specification and development
Evolutionary
Specification and development are interleaved
Formal Transformation
A mathematical system model is formally transformed to an implementation
Reuse-based
The system is assembled from existing components
Waterfall Process Model : Waterfall Process Model
Evolutionary Process Model : Evolutionary Process Model
Process Model Problems : Process Model Problems Waterfall
High risk for new systems because of specification and design problems.
Low risk for well-understood developments using familiar technology.
Prototyping
Low risk for new applications because specification and program stay in step.
High risk because of lack of process visibility.
Transformational
High risk because of need for advanced technology and staff skills.
Hybrid Process Models : Hybrid Process Models Large systems are usually made up of several sub-systems.
The same process model need not be used for all subsystems.
Prototyping for high-risk specifications.
Waterfall model for well-understood developments.
Spiral Process Model : Spiral Process Model
Spiral Model Advantages : Spiral Model Advantages Focuses attention on reuse options.
Focuses attention on early error elimination.
Puts quality objectives up front.
Integrates development and maintenance.
Provides a framework for hardware/software development.
Spiral Model Problems : Spiral Model Problems Contractual development often specifies process model and deliverables in advance.
Requires risk assessment expertise.
Process Visibility : Process Visibility Software systems are intangible so managers need documents to assess progress.
Waterfall model is still the most widely used model.
Waterfall Model Documents : Waterfall Model Documents
Process Model Visibility : Process Model Visibility
Professional Responsibility : Professional Responsibility Software engineers should not just be concerned with technical considerations. They have wider ethical, social and professional responsibilities.
No clear rights and wrongs about many of these issues:
Development of military systems
Whistle blowing
Ethical Issues : Ethical Issues Confidentiality
Competence
Intellectual property rights
Computer misuse