Software abstraction and modelling

Question 1

Software design

Answer 1

The activity of constructing models representing:

• abstractions of data and computation
• the organization of these abstractions into a working
  software system

Question 2

Features of a good model

Answer 2

• mapping feature: a model is based on an original (=system)
• reduction feature: a model only reflects a (relevant) selection of the original‘s properties
• pragmatic feature: A model needs to be usable in place of an original with respect to some purpose

Question 3

who does what

Answer 3

picture

Question 4

descriptive <-> prescriptive

Answer 4

subject is described by <-> prescribes the subject

Question 5

descriptive models

Answer 5

Sketches and throw-away models
- to better understand reality and to explore possible solutions
- short lifetime (usually)
- Models of ideas and vision about the system to be developed
- to exploit the model for having feedback before implementing the system
- Models extracted from a running system or source code
- for example, to visualise all possible calls between a set of
Java classes

Question 6

prescriptive models

Answer 6

• They guide the development of the system
  
  • more detailed than descriptive models
  • specify constraints for the system
• Common consumers of prescriptive models are developers or code generators (model-driven engineering - MDE)
• Prescriptive models are often used for development
  
  • their importance might decrease when the system is implemented

Question 7

informal notations

Answer 7

• Ad-hoc visualizations with no clear semantics
• Examples: “box-and-line” or PowerPoint diagrams

Question 8

semiformal notations

Answer 8

• Standardised graphical elements and construction rules, semantics are mostly specified to allow basic analysis
• Examples: UML (we will use it extensively in this course)

Question 9

formal

Answer 9

• Precise semantics based on mathematical constructs that allow full formal analysis for syntax and semantics
• Examples: architecture description languages (ADLs), e.g., Acme, AADL, AUTOSAR

Question 10

Software design vs. software architecture

Answer 10

• Software design is the activity of creating an architecture
• Software architecture is concerned with high-level, coarse-grained structures and decisions of a system
• Software design is concerned with more local, fine-grained structures and decisions

Question 11

Why do we need (architecture and) design?

Answer 11

• They enable reasoning about large systems
  → abstractions and hierarchies help to manage complexity
• They are the driver for software quality (not what the system does, but how it does it)
• They enable separating a system into parts to let teams work on them in parallel
• They are the bridge between the requirements and the implementation