practise

• during the practical classes, the students explore and document the requirements of a software system
  • using user story mapping in accordance with the agile principles
• then, during the second half of the semester, they design its architecture
  • using the C4 model, which is a set of hierarchical diagrams describing the architecture of a software system
• the practical classes are workshops in which the students work in teams
  • under an instructor’s guidance

program is like a recipe

for i in range(1, 101):
    if i % 15 == 0:
        print("" + "FizzBuzz")
    elif i % 3 == 0:
        print("" + "Fizz")
    elif i % 5 == 0:
        print("" + "Buzz")
    else:
        print(i)

software development not is like building a house

a software does not have to obey the laws of physics

• in software development you can start with the door of the second floor bathroom
• the size of a room can be changed during the construction – even several times

what is software rot?

dormant rot: the software in question is not changed, but as the environment evolves, it eventually becomes dysfunctional

Muni metro’s control software is still loaded from floppy disks [4]

software development is like gardening - cont.

how big are softwares?

software is often measured by the source lines of code

software growth

number of lines of code is increasing

why does software grow?

software growth – aircrafts

24 million lines of code – operational and support – needed for the F-35 to be fully operational; when the program started, the estimated number of lines of code required was closer to 15 million

– Robert N. Charette, F-35 Program Continues to Struggle with Software [6]

software growth – car industry

• 1981, GM was using microprocessor-based engine controls executing about 50 000 lines of code [8]
• even low-end cars now [2009] have 30 to 50 electronic control units (ECUs)
  • that means these cars “execute” tens of millions of lines of software code that control everything from your brakes to your radio volume [8]
• in a modern car [2023], you can expect to find 50 to over 100 ECUs [9]
• for hybrids, the amount of software required for engine control is almost double that of a standard car [8]

the more, the better?

if we wish to count lines of code, we should not regard them as “lines produced” but as “lines spent”

E. W. Dijkstra EWD 1036

keep it simple

Linux 5.8 – 800,000 new lines of code

• how is it manageable?
  • process
  • version control
• each change must do only one thing
  • proper documentation
• changes cannot break the software
  • rigorous and automated testing

why you should use version control (for everything)

benefits of version control systems

• generate backups
• separates experiments from the working version
  • branching, deployment strategies (much later in the course)
• keep history and track changes
  • traceability
• foster collaboration and contribution
  • team work

The current level of software complexity is not manageable without allowing many people to work on the same code base, and the separation of the development versions from the production one.

is it possible to decrease the dependency stack?

reimplementation costs

complexity classes

from Michael Bykovski’s essay [14]

• in a simple system, we know the knowns, everything is predictable, it’s easy to understand the system
• in a complicated system, we know the knowns and unknowns
  • it requires analysis to know the unknowns, but the system is measurable
  • it is the province of engineers, surgeons, intelligence analysts, lawyers, and other experts [15]
• in a complex system, the knowns are unknown to us, but we are aware of our uncertainty
• a chaotic system is a system of unknown unknowns

project complexity – Cynefin framework

• Cynefin framework is a conceptual framework used to aid decision-making
  • cynefin (/kəˈnɛvɪn/ kuh-NEV-in) is a Welsh word for ‘habitat’
  • created by Dave Snowden
• defines five decision-making contexts or “domains”
  • clear (aka simple)
  • complicated
  • complex
  • chaotic
  • confusion (or disorder)
• you can read more on Wikipedia

project complexity

In most successful software projects, the expert developers working on that project have a shared understanding of the system design. This shared understanding is called ‘architecture’. This understanding includes how the system is divided into components and how the components interact through interfaces. These components are usually composed of smaller components, but the architecture only includes the components and interfaces that are understood by all the developers.

Ralph Johnson, XP mailing list

All architecture is design but not all design is architecture. Architecture represents the significant design decisions that shape a system, where significant is measured by cost of change.

– Grady Booch

so, architecture

# Title

## Status

What is the status, such as proposed, accepted,
rejected, deprecated, superseded, etc.?

## Context

What is the issue that we're seeing that is
motivating this decision or change?

## Decision

What is the change that we're proposing and/or doing?

## Consequences

What becomes easier or more difficult to do
because of this change?

what are these decisions?