CS 310 Ch 4: Software Processes Software process: a set of activities that lead to a software system specification design and implementation validation evolution Software process model: an abstract representation of a process describes a process from some particular perspective What processes do you use? Why do we want a standardized model?

4.1 Software process models The waterfall model separate and distinct phases of specification and development Evolutionary development specification and development are interleaved Formal systems development a mathematical system model is formally transformed into an implementation Component-based development the system is assembled from existing components Questions for later: which is most widely used in web development? what would you use for WELLS-AC?

4.1.1 Waterfall model Digicomp original air surveillance system. Drawback: difficulty of incorporating change after a stage is passed (documentation at each step)

4.1.2 Evolutionary development Also called rapid prototyping Also called "build a little/code a little/test a little"

Evolutionary development Problems lack of process visibility systems are often poorly structured Applicability small or medium-size interactive systems parts of large systems (e.g. the user interface) short-lifetime systems systems with some margin for error

4.1.x Formal systems development “Transformations are ‘correctness-preserving’ so it is straightforward to show that a program conforms to its specification” CCS comment: 1) don’t believe it. 2) this method is very rarely used

4.1.3 Component-based development Systems are built from existing components or COTS Digicomp current air surveillance system assemble software components purchase hardware (computers, terminals,…) purchase commercial software (operating system, radar interface sw…) edit configuration files put it on a truck, install, test, train users The approach is increasingly important. Why?

Selecting a model Web development waterfall? evolutionary? component-based? WELLS-AC waterfall? evolutionary? component-based?

4.2 Process iteration (skip) System requirements ALWAYS evolve during a project Process iteration where earlier stages are reworked is always part of building large systems 4.3 Process activities Specification Design and implementation Validation Evolution

4.3.1 Software specification Software specification/requirements engineering: establishing required services and system constraints

4.3.2 Software design and implementation Converting the specification into the usable system Design (one view, more later): Have you ever designed anything?

4.3.3 Software validation Verification and validation:* intended to show that a system conforms to its specification and meets the requirements of the customer * validation usually tests that we building what the customer wants verification usually tests that the system meets its spec V&V here

Testing phases

4.5 Computer Assisted Software Engineering (CASE) - skim Software to support development and evolution Activity automation graphical editors for system model development data dictionary to manage design and code entities graphical UI builder for user interface construction debuggers to support program fault finding Levels tools to support individual process tasks such as design consistency checking, text editing, etc. workbenches to support a phase such as specification or design, normally including a number of integrated tools environments to support the entire software process

Tools, workbenches, environments What tools do you know?