Software Engineering A Practitioners Approach 7e Chapter 2

Software Engineering: A Practitioner’s Approach, 7/e Chapter 2 Prescriptive Process Models copyright © 1996, 2001, 2005 R. S. Pressman & Associates, Inc. For University Use Only May be reproduced ONLY for student use at the university level when used in conjunction with Software Engineering: A Practitioner's Approach. Any other reproduction or use is expressly prohibited. Coming up: Prescriptive Models 1

Last time: Different families of models Prescriptive Agile Goal: Higher Quality Software Philosophy: • Bring order to chaos • Provide repeatability/consistency • Provide ability to control • Provide ability to coordinate teams • Individuals and interaction over process and tools • Working software over large documentation • Customer collaboration over contract negotiation • Responding to change over following a plan 2

Last time n n We discussed how prescriptive models seems to have lost their popularity, while agile models have been gaining in popularity What are some possible reasons for this?

Prescriptive Models Prescriptive process models advocate an orderly approach to software engineering That leads to a few questions … n If prescriptive process models strive for structure and order, are they inappropriate for a software world that thrives on change? n 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? n Coming up: The Waterfall Model 4

The Waterfall Model Use when: -Requirements are stable and well-understood, very short timeline (maintenance fixes) Coming up: The V-Model 5

Why was the waterfall model designed? n n Invented in 1970 It is frequently true that time spent at the beginning of the product lifecycle cuts down on the work in later stages n n How much time does maintenance consume? The biggest lesson learned is that waterfall models n n Generally don’t work Because it’s unrealistic to not have change

The V-Model Same as Waterfall, diagram used to emphasize types of testing are linked to different phases in the model -Requirements are stable and wellunderstood Coming up: The Incremental Model 7

The V model n Focuses on verification and validation

The Incremental Model Coming up: The Incremental Model 9

The Incremental Model Requires: Operational product that provides some value to users at each increment. Advantages -Helps users get software faster -Provides ability for the team to evaluate and replan -May complete an initial functionality to get buyin or funding for later increments Disadvantages -May not be good for very risky systems -Full working systems may require long increments Coming up: The RAD Model 10

The RAD Model Coming up: The RAD Model 11

The RAD Model RAD = Rapid Application Development Requires: very well understood requirements. Very fast cycles (60 -90 days) to create a lot of functionality Emphasizes use of existing components/ automatic code generation Challenges: - Large staff needed to form RAD teams - Must have modularizable based software - Developers and Customers must be willing to make quick decisions - Time-consuming overall system tuning is difficult Coming up: Evolutionary Models: Prototyping 12

Evolutionary Models: Prototyping Used when partial system can be delivered, then evolved into full system communication Prototyping is a tool that can be used during any process Used when customer only has a vague idea of what they want Plan to either throw-away or evolve into real product -there will be pressure at the end to evolve into the real product Coming up: Evolutionary Models: The Spiral Quick plan Modeling Quick design Deployment delivery & feedback Construction of prototype 13

Evolutionary Models: The Spiral Complete highest risk items first Used to mitigate risk on riskintensive projects Every spiral revises cost/budget/sche dule/etc… Coming up: Still Other Process Models 14

Still Other Process Models n n 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) Coming up: The Unified Process (UP) 15

Can you guess which company uses the spiral model?

The Unified Process n What is it? n n n Phases: inception, elaboration, construction, transition The phases are divided up into time-boxes (iterations) Each of these iterations results in some deliverable increment

UP Phases Coming up: UP Work Products 20

UP Work Products Coming up: Pick a model 21

Pick a model n Developing software to automatically drive racecars through a track without crashing. This has never been attempted before under software control. The requirements are stable. n Waterfall, Incremental, Spiral, RAD? Coming up: Pick a model 22

Pick a model n Developing software to track the financial bailout. The software requirements are very clear. You need to create a system to perform 3 distinct tasks: n n n Display where the money went Display the amount of money left and how it’s allocated Allow people to request funds from a particular subset of the money All functions will interface with each other and the same underlying database. Waterfall, Incremental, Spiral, RAD? Coming up: Pick a model 23

Pick a model n Just checking if you were awake Coming up: Prescriptive Software Models 25

Prescriptive Software Models n n Variations of these models are VERY commonly used today If you think about it, they are focused in different areas, but have many similarities (all do the basic structure -- communication, planning, construction, testing, deployment, maintenance) You will almost definitely do some version of these processes when you graduate If you had never been to CS 421, and never learned them, and then started your own company, you would STILL do your own version of these processes… they make sense! End of presentation 26