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Software Engineering Process and Models. A Layered Technology Software Engineering a “quality” focus process model methods tools.

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Presentation on theme: "Software Engineering Process and Models. A Layered Technology Software Engineering a “quality” focus process model methods tools."— Presentation transcript:

1 Software Engineering Process and Models

2 A Layered Technology Software Engineering a “quality” focus process model methods tools

3 A Process Framework Process framework Framework activities work tasks work products milestones & deliverables QA checkpoints Umbrella Activities

4 Framework Activities Communication Planning Modeling –Analysis of requirements –Design Construction –Code generation –Testing Deployment

5 Umbrella Activities Software project management Formal technical reviews Software quality assurance Software configuration management Work product preparation and production Reusability management Measurement Risk management

6 The Process Model: Adaptability the framework activities will always be applied on every project... BUT the tasks (and degree of rigor) for each activity will vary based on: –the type of project –characteristics of the project –common sense judgment; concurrence of the project team

7 Assessment and Improvement

8 The Primary Goal of Any Software Process: High Quality Remember: High quality = project timeliness Why? Less rework!

9 What are the attributes of good software? Maintainability –Software must evolve to meet changing needs Dependability –Software must be trustworthy Efficiency –Software should not make wasteful use of system resources Usability –Software must be usable by the users for which it was designed The software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable

10 What are the key challenges facing software engineering? Software engineering in the 21 st century faces three key challenges: Legacy systems –Old, valuable systems must be maintained and updated Heterogeneity –Systems are distributed and include a mix of hardware and software Delivery –There is increasing pressure for faster delivery of software

11 What is a software process? SP is a set of activities whose goal is the development or evolution of software Fundamental activities in all software processes are: –Specification - what the system should do and its development constraints –Development - production of the software system (design and implementation) –Validation - checking that the software is what the customer wants –Evolution - changing the software in response to changing demands

12 What is a software process model? SPM is a simplified representation of a software process, presented from a specific perspective Examples of process perspectives: Workflow perspective represents inputs, outputs and dependencies Data-flow perspective represents data transformation activities Role/action perspective represents the roles/activities of the people involved in software process Generic process models –Waterfall –Evolutionary development –Formal transformation –Integration from reusable components

13 What is a Process … ? When we provide a service or create a product we always follow a sequence of steps to accomplish a set of tasks –You do not usually put up the drywall before the wiring for a house is installed or bake a cake before all the ingredients are mixed together We can think of a series of activities as a process Any process has the following characteristics –It prescribes all of the major activities –It uses resources and produces intermediate and final products –It may include sub-processes and has entry and exit criteria –The activities are organized in a sequence –Constrains or control may apply to activities (budget control, availability of resources )

14 Software Processes Coherent sets of activities for –Specifying, –Designing, –Implementing and –Testing software systems When the process involves the building of some product we refer to the process as a life cycle Software development process – software life cycle

15 Major problems in software developments … The requirements specification was defined like this The developers understood it in that way This is how the problem was solved before. This is how the problem is solved now That is the program after debugging This is how the program is described by marketing department This, in fact, is what the customer wanted … ;-)

16 The Software Process A structured set of activities required to develop a software system –Specification –Design –Validation –Evolution A software process model is an abstract representation of a process –It presents a description of a process from some particular perspective

17 Generic Software Process Models The waterfall model –Separate and distinct phases of specification and development Evolutionary development –Specification and development are interleaved Formal systems development (example - ASML) –A mathematical system model is formally transformed to an implementation Reuse-based development –The system is assembled from existing components

18 1. Waterfall Model

19 Prescriptive Models Prescriptive process models advocate an orderly approach to software engineering That leads to a few questions … If prescriptive process models strive for structure and order, are they inappropriate for a software world that thrives on change? Yet, if we reject traditional process models (and the order they imply) and replace them with something less structured, do we make it impossible to achieve coordination and coherence in software work?

20 The Waterfall Model

21 Waterfall model phases R equirements analysis and definition S ystem and software design I mplementation and unit testing I ntegration and system testing O peration and maintenance The drawback of the waterfall model is the difficulty of accommodating change after the process is underway

22 Waterfall model problems Inflexible partitioning of the project into distinct stages This makes it difficult to respond to changing customer requirements Therefore, this model is only appropriate when the requirements are well-understood Waterfall model describes a process of stepwise refinement  Based on hardware engineering models  Widely used in military and aerospace industries

23 Why Not a Waterfall But software is different :  No fabrication step  Program code is another design level  Hence, no “commit” step – software can always be changed…!  No body of experience for design analysis (yet)  Most analysis (testing) is done on program code  Hence, problems not detected until late in the process  Waterfall model takes a static view of requirements  Ignore changing needs  Lack of user involvement once specification is written  Unrealistic separation of specification from the design  Doesn’t accommodate prototyping, reuse, etc

24 2. Evolutionary development Exploratory development -Objective is to work with customers and to evolve a final system from an initial outline specification. -Should start with well-understood requirements. -The system evolves by adding new features as they are proposed by customer. Throw-away prototyping –Objective is to understand the system requirements. Should start with poorly understood requirements Develop “quick and dirty” system quickly; Expose to user comment; Refine; Until adequate system developed. –Particularly suitable where: -detailed requirements not possible; -powerful development tools (e.g. GUI) available

25 Evolutionary Models: Prototyping communication Quick plan Modeling Quick design Construction of prototype Deployment delivery & feedback

26 Evolutionary Models: The Spiral

27 Evolutionary Models: Concurrent

28 The Incremental Model

29 The RAD Model

30 Still Other Process Models Component based development—the process to apply when reuse is a development objective Formal methods—emphasizes the mathematical specification of requirements AOSD—provides a process and methodological approach for defining, specifying, designing, and constructing aspects Unified Process—a “use-case driven, architecture- centric, iterative and incremental” software process closely aligned with the Unified Modeling Language (UML)

31 inception The Unified Process (UP) inception elaboration

32 UP Phases

33 UP Work Products


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