Software development typically aims to align specifications with implementation.
For this reason, systems are designed to fulfill specifications, and then implemented based on those designs. Subsequently, testing confirms that the implementation meets the specifications; if there's a discrepancy, the implementation is corrected, and if specifications are ambiguous, they are clarified.
This can be called Specification and Implementation-Based Engineering.
In contrast, when discussing software today, user experience is increasingly emphasized.
Furthermore, it is the behavior of the software, not its mere implementation, that actually shapes the user experience.
Therefore, outside the framework of specification and implementation, there exist experience and behavior.
Consequently, I believe it is worthwhile to explore the concept of Experience & Behavior Engineering, which is based on experience and behavior.
Liquidware
Experience & Behavior Engineering is an impractical approach with traditional software development methods.
This is because it requires improving the user's experience without rigid boundaries or functional divisions in specifications. There might even be cases where a casual user request for an experience improvement would necessitate discarding all previously developed software.
On the other hand, in an era where agent-based software development automation by generative AI is commonplace, rebuilding entire software systems becomes acceptable.
Moreover, in such an era, it is conceivable that we will enter the age of Liquidware, where developers release software equipped with an AI engineer chatbot, allowing users to modify the UI to suit their individual preferences.
Liquidware signifies software that is more flexible than conventional software, fitting each user perfectly.
With this era of automated development and Liquidware, the engineering paradigm of specification and implementation will become obsolete.
Instead, we will transition to the paradigm of Experience & Behavior Engineering.
What is Behavior?
Simply put, behavior is a state that changes over time.
And testing behavior is nothing other than testing this time-varying state.
Furthermore, testing behavior is not about confirming alignment with specifications that define how states transition. Rather, behavior is tested by the quality of the user's experience.
Of course, if there are bugs that cause the system to perform operations unintended by the user or developer, this significantly detracts from the user experience. Therefore, testing behavior also includes verifying functional conformity and validity.
Thus, after fulfilling these basic functional requirements, behavior is tested for its high quality from the perspective of user experience.
The Ultimate Experience
For humans, the ultimate user experience is the control of one's body when in good health.
Consider this: every day, we control a body weighing tens of kilograms—a complex system filled with limitations and constraints—to engage in purposeful activities.
If we were to try to control such a heavy, complex, and highly constrained system to perform desired activities, the experience would typically be quite poor.
Yet, as long as we are not unwell, we move this heavy, complex, and constrained body as effortlessly as if it had no weight at all. We operate it without hesitation, as if it were a very simple mechanism, and hardly notice its limitations or constraints, as if they didn't exist.
This is the ultimate experience.
By pursuing high-quality behavior, it's possible to provide an experience on par with that of controlling one's own body.
In other words, even if a system is slow to process, complex in functionality, and subject to many limitations and constraints, it could become Liquidware that is entirely stress-free.
Conclusion
The ultimate Liquidware will offer an experience akin to that of our own bodies.
Such Liquidware will become, for us, like a part of our physical selves.
Every time ultimate Liquidware increases in number or its capabilities are enhanced, it will feel as if our bodies are being extended.