Lecture 4: Software Lifecycle

Question 1

Definition SW Lifecycle

Answer 1

• Software life cycle (also called software process)
  
  • Set of activities and their relationships to each other to support the development of a software system
• Software life cycle model:
  
  • An abstraction that represents a software life cycle for the purpose of understanding, monitoring, or controlling the development of a software system.

Question 2

Where do we need Models?

Answer 2

Models support three different types of activities:

• Communication: The model provides a common vocabulary. An informal model is often used to communicate an idea
• Analysis/Design: Models enable developers to reason about the future system
• Archival: Compact representation for storing the design and rationale of an existing system.

Question 3

How much Modeling? Advantage Problem

Answer 3

• Advantages of modeling:
  
  • Modeling enables developers to deal with complexity
  • Modeling makes implicit knowledge about the system explicit
  • Modeling formalizes knowledge so that a number of participants can share it
• Problem with modeling:
  
  • If one is not careful, models can become as complex as the system being modeled.

Question 4

Models that support Communication

Answer 4

• Also called communication models (conceptual models)
• Most often used in the early phases of a project and during informal communications
  
  • The model does not have to be consistent or complete
  • The notation does not even have to be used correctly
• The model is used only to communicate an idea to a person
  
  • If the idea is understood, the model has served its purpose
• Informal models are our preferred way to support communication
• Communication Media:
  
  • • A Whiteboard, a mockup, or even a napkin design.

Question 5

Models that support Analysis and Design

Answer 5

• Also called specification models
• The model provides a representation that enables developers to reason about the system
• The model is used to communicate the idea to a tool
  
  • The model needs to be made consistent and complete
  • The notation must be correct so the model can be entered into a CASE tool
• UML is our preferred notation for models to models that support analysis and design.

Question 6

Managerial Challenges of Modeling

Answer 6

• Formalizing knowledge is expensive
  
  • Takes time and effort from developers
    
    • Antipattern: Analysis Paralysis
  • Requires validation and consensus
• Models introduce redundancy
  
  • If the system is changed, the models must be changed
  • If several models depict the same aspects of the system, all of them must be updated
  • If one model becomes out of sync, it loses its value
• Models become complex
  
  • As the model complexity becomes similar to the complexity of the system, the benefit of having a model is reduced significantly.

Question 7

Typical Software Life Cycle Questions

Answer 7

• Which activities should we select for the software project?
• What are the dependencies between activities?
• How should we schedule the activities?

Question 8

Tailoring

Answer 8

• • There is no “one size fits all” software lifecycle model that works for all possible software engineering projects
• Tailoring: Adjusting a lifecycle model to fit a project
  
  • Naming: Adjusting the naming of activities
  • Cutting: Removing activities not need in the project
  • Ordering: Defining the order the activities take place in.

Question 9

Modeling a Software Lifecycle

Answer 9

We can use the same modeling techniques we use for software development:

• Functional model of a Software Lifecycle
  
  • Scenarios, user stories
  • Use case model
• Structural model of a Software Lifecycle
  
  • Object identification
  • Class diagrams
• Dynamic model of a Software Lifecycle
  
  • Sequence diagrams, statechart and activity diagrams

Question 10

Functional Model of a simple Life Cycle

Answer 10

Question 11

Activity Diagram for the Life Cycle

Answer 11

Software development goes through a linear progression of states called problem definition activity, software development activity and system operation activity.

Question 12

Two Major Views of the Software Life Cycle

Answer 12

• Activity-centered view of a software life cycle
  
  • Software development consists of a set of development activities
• Entity-centered view of a software life cycle
  
  • Software development consists of the creation of a set of deliverables.

Question 13

Process Groups, Processes, Activities and Tasks

Answer 13

• Process Group: Consists of a set of processes
• Process: Consists of activities
• Activity: Consists of sub activities (phases, steps,…) and tasks

Question 14

Process Groups exapmle

Answer 14

Question 15

Waterfall Model (Royce 1970)

Answer 15

• An activity-centered life cycle model that prescribes a sequential execution of activities
  
  • The model assumes that software development can be scheduled as a step-by-step process that transforms user needs into code.
  • The goal is to never turn back once an activity is completed
• The key feature of the model is the verification activity (called “verification step” by Royse) at the end of each activity that ensures that the activity does not introduce unwanted or deletes mandatory requirements
• The model provides a simplistic view of software development that measures progress by the number of tasks that have been completed.

Question 16

Waterfall model example

Answer 16

• Required by the U.S. Department of Defense for all software contractors in the 1980-90’s

• Software development activities:
• System Requirements Analysis/Design

• Software Requirements Analysis
• Preliminary Design and Detailed Design • Coding and CSU testing
• CSC Integration and Testing
• CSCI Testing
• System integration and Testing.

Question 17

V-Model

Answer 17

• The horizontal object flow denotes the information flow between activities of same abstraction level
  
  • Of course, the layout of the activities has no semantics in UML
• Higher levels of abstractions of the V-model deal with the requirements in terms of elicitation and operation
  
  • The Client Acceptance Activity validates the understanding of the user against the requirements
• The middle-part of the V-model focuses on mapping the understanding of the problem into a software architecture
  
  • The Component Integration and Test activity validates functional components against the preliminary design
• The lower level of the V-model focuses on details such as the assembly and coding of software components
  
  • Unit Test activity validate units against their description in the detailed design.

Question 18

Properties of Waterfall-based Models

Answer 18

• Managers love waterfall models
  
  • Nice milestones
  • No need to look back (linear system)
  • Always one activity at a time
  • Easy to check progress during development: 90% coded, 20% tested
• However, software development is non-linear
  
  • While a design is being developed, problems with requirements are identified
  • While a program is being coded, design and requirement problems are found
  • While a program is tested, coding errors, design errors and requirement errors are found.

Question 19

Definition: Iterative vs. Incremental

Answer 19

• Iterative means “re-do” or “re-work”
  
  • Iterative development helps you to improve your product
• Incremental means “to add onto something”
  
  • Incremental development helps you improve your process
• Incremental development:
  
  • A strategy where the various parts of the system are developed at different times or rates and integrated as they are completed
• Iterative development:
  
  • A strategy in which time is set aside to revise and improve parts of the system.

Question 20

Increments can cause iterations

Answer 20

• Product iteration can result from incremental addition of functionality that had not been anticipated in a previous iteration
  
  • Example: If you do a functional baseline that runs through subsystems A and B and then you do another functional baseline that runs through A and C, in a lot of cases you’ll have to do at least some rework on A
• This is why it’s good to anticipate requirements to a certain degree to mitigate the level of disruption
• Product iteration can also result from restructurings
  
  • Examples: Cleanups of code smells, introduction of refactored solutions in antipatterns, introduction of new technology, architectural redesign.

Question 21

Which of the following statements are correct?

Select one or more:

a. The project manager must be involved in problem definition
b. The project manager must be involved system development activities
c. A functional model of a software life cycle includes class and sequence diagram
d. Testing and implementation can be done in parallel

Answer 21

b,d

Question 22

What are software projects activities?
Select one or more:
a. Requirement analysis
b. Testing
c. Merging source control’s branches
d. Program implementation
e. Delivery

f. Model design maintenance

Answer 22

a,b,d,e

Question 23

The functional model of software lifecycle contains

Select one or more:

a. scenarios
b. user stories
c. class diagrams
d. use case models
e. state charts
f. sequence diagrams

Answer 23

a,b,d

Question 24

Tailoring includes

Select one or more:

a. defining the order the activities take place in
b. reviewing the contract of the project
c. forming teams of programmers with different backgrounds
d. adjusting a lifecycle model to fit a project
e. removing activities not needed in the project

Answer 24

a,d,e

Question 25

Which of the following statements are correct?

Select one or more:

a. Whiteboard drawing is a specification model
b. Client Review is a communication mechanism
c. Napkin Design is a communication model
d. Email is a communication mechanism
e. Meeting is a communication event
f. An object model is a specification model

Answer 25

c,d,e,f

Question 26

A communication model is
Select one or more:
a. used to pass information to a tool
b. used to perform testing
c. must be complete and fully consistent
d. used during the early phases

Answer 26

d