A Guide to Systems Engineering (SE)

Are you familiar with Systems Engineering (SE)?

As far as I remember, this is how it became a topic of discussion in Japan.

As of 2026, I believe the term Systems Engineering (or MBSE) has spread to a wide range of fields (it's becoming more common in business contexts as well).

However, in my experience, even though systems engineering has become widespread, it is still prevalent in certain fields, especially in the IT sector (the V-process remains popular in the automotive industry).

Systems engineering, in its true form, is not a methodology specialized for a particular field, but rather a general-purpose methodology that can be applied to a wide range of areas (it originally started in military logistics).

In fact, this technique is extremely useful not only in business settings but also for improving your everyday life and your way of thinking.

I'm starting a series where I'll explain systems engineering (SE), which is likely to become increasingly important in the future, drawing on my own practical experience in my work.

I'll continue to write "Systems Engineering" but it's tedious, so from now on I'll abbreviate it as SE. However, it's important to note that this is completely different from the SE (Systems Engineer, etc.) used in the Japanese context.

This is the momentous first installment of "An Introduction to Systems Engineering" (structurally, this is the zeroth installment).

What is systems engineering?

It's extremely difficult to condense and summarize systems engineering simply, so I'll borrow some words from INCOSE.
(INCOSE is an abbreviation for the International Council on Systems Engineering.)

As expected of academic language. It's so abstract that I can barely understand the specifics (I can barely grasp the general idea, though).

Let me rephrase that slightly.

Has it gotten a little better?

To give a concrete example from actual history, it's a methodology for optimizing and successfully managing massive and complex projects like World War II or the Apollo program (the United States actually has a history of using SE to successfully complete projects).

The key point here is the system and methodology, so let me briefly explain them.

What does "system" mean in the context of SE (Systems Engineering)? (What is the true meaning of the English word "system" in the first place?)

The word "system" is frequently used in Japan, but its meaning is quite ambiguous (I think it's a mistranslation in the first place).

Let's clarify the meaning of "system" in the context of SE (Systems Engineering).

Let's start by borrowing a phrase from INCOSE.

Impressive. Again, I don't quite understand.

Let's use a concrete example to help you grasp the concept.

We will consider automobiles as a system based on their definition. A detailed explanation of how to view and develop this system will be provided in a separate article, so for now, a general understanding is sufficient.

First, let's consider the combinations of elements that interact within a car.

As you can imagine if you picture a real car, an automobile is made up of a body, powertrain, and chassis that interact with each other.
*There may be disagreements, but please consider this to be the minimum necessary element.

In other words, in the field of systems engineering, a car is considered a "system."

Furthermore, we will consider the powertrain, which is the author's area of ​​expertise, as a system.

The powertrain, a component of an automobile, is also considered a system in SE (System Engineering) because it is composed of a combination of interacting elements.

In other words, in system engineering, anything composed of multiple interacting elements can be considered a system.

Let's consider the Japanese government as a system in the context of software engineering (this is a very simplified example).

The Japanese government, too, is striving to achieve a stable life for its citizens through the interaction of many individual elements (the Cabinet, various ministries, etc.).
*Unfortunately, there may be little interaction between the individual elements (vertical administration).

Thus, in SE (Systems Engineering), we don't just consider things as systems; we can also consider things that don't have a physical form, like the Japanese government, as systems.

In other words, a system in SE is,A collection of many interacting elements that come together to form a single large entity that performs its intended function.If that's the case, then anything—anything, any event, any organization—can be conceived as a system.

If we consider small elements as individual systems or subsystems, then a large entity is a collection of subsystems, and is therefore sometimes called a system of systems.
*The plural form "systems engineering" is used because it deals with a collection of multiple systems.

You can see that the word "system" as it's commonly used in Japan has a completely different meaning. Incidentally, the dictionary definition of "system" in Japanese is "system" or "system."
I believe that the continued misuse of the term "mass media system" is one of the major reasons why Japan is unable to recover.

In this way, SE views everything as a system. The main purpose of this isTo enable us to think about complex things by breaking them down into individual elements (subsystems).

in shortIt's difficult to think of complex things as a whole, so we break them down into elements that we can understand, and then integrate them at the end.That is its most distinctive feature.

This is a very useful way of thinking in everyday life, and it is exceptionally effective for understanding complex phenomena and things.

SE is a methodology (not a solution).

The next important point is that SE is a methodology. It is a methodology, and it is not something that "discovers the answer to a problem and solves it."

For example, let's consider a typical simulation where "the answer to a problem is revealed and solved" (in reality, simulations cannot provide either an answer or a solution to a problem).

SE is completely different from simulation-like methods; it is the process itself that guides you on "how to approach the problem, what to think about, and what to do" (it's a different layer).

Let's look at some more specific examples.

I think you can see that all of these are specific and potential solutions (whether they actually completely solve the problem is another matter).

SE allows you to obtain solutions that go beyond specific, individual measures, such as the following approaches.

As you can see from this, the SE methodology is a process of "how to find the answer."

The reason this methodology is important is that, in today's complex and advanced problems, there is rarely a single correct answer.

For example, to achieve the goal of creating a fuel-efficient car, the following technologies come to mind:

All of these are correct, but the demands of today's complex and sophisticated problems far exceed what can be overcome with a single solution (such as Euro 7 emissions regulations).

A single solution is no longer sufficient; we need to find the optimal combination of factors—cost, time, technical difficulty, market needs, and more—to solve the problem.

SE is thisThis is a methodology that systematizes the process of finding the optimal solution.SE is sometimes called a "best practice" because it's a methodology.

Hopefully, this has given you a general understanding that SE is a methodology.

A Recommendation for SEs

Here, I will explain why I recommend becoming a systems engineer (SE).

The reason I recommend SE is...Explosive increase in complexityThis is because it is one of the most useful ways to address the issue (such as in the development of sophisticated products like automobiles and related policies).

Basically, human society is becoming more complex, and in modern times, this complexity is increasing at an accelerating rate.

Even comparing only the number of parts in an automobile, the increase is as follows:

• Automobiles from the 1960s: Approximately 3,000 parts, primarily mechanical.

• Automobiles in the 2020s: Approximately 30,000 parts, mechanical + electrical + software + communication

While the number of parts is ten times greater, the complexity of how these parts are combined increases by more than 100 times (because the interactions between parts increase exponentially).

This complexity arises because, in addition to the classic function of the automobile—the free movement of people—various functions from different fields are added as time progresses.

In the past, automobile development and manufacturing could be done solely by people with mechanical engineering backgrounds, but nowadays, people from various fields such as electrical engineering, electronics, software, and communications are needed in addition to mechanics.

Furthermore, with modern automobiles, the relationship doesn't end with the sale; ongoing support such as maintenance, repairs, handling of market defects (recalls, etc.), and vehicle inspections are essential while the user is using the vehicle.

Furthermore, given the growing environmental concerns in recent years, we must also consider disposal methods such as recyclability (simply scrapping and throwing away materials is no longer legally permitted).

Even this brief overview of automobiles should give you an idea of ​​just how complex they have become (so complex that it's almost unbearable to think about).

This increasing complexity is not limited to automobiles; it is spreading to virtually every field, including healthcare, urban infrastructure, manufacturing, the IT industry, service industries, and even policymaking.

Why are SEs effective in dealing with complexity?

So, why is SE (Systems Engineering) effective in dealing with this complexity?

In traditional development, each department proceeded with development based on experience, intuition, and coordination between departments, and finally integrated and verified through testing.

Even with automobiles, if the number of parts was 3,000 and the number of people involved was only a few dozen, it was manageable (in fact, automobile development in the 1960s involved around a few dozen people).

However, when you have 30,000 parts, hundreds of people involved, and more than 10 areas of expertise, experience, intuition, and fine-tuning alone are no longer sufficient.

The benefits of this SE approach include, as listed below.

In other words, SE is a systematic methodology for breaking down complexity into manageable levels and integrating them.Therefore, it has become a very effective method for dealing with increasingly complex problems.
*As explained above, this is about viewing things as a system and breaking them down into elements that can be understood.

However, you might be wondering, "Is it really that effective?"

In fact, SE (Systems Engineering) has a history that began with logistics management during World War II, achieved great success with the Apollo program, and has continued to develop to the present day.

In the next chapter, we will look at the history of how software engineers (SEs) were born and what successes (and failures) they have experienced. Understanding this history will allow you to gain a deeper understanding of the essence of SEs.

The History of SE

To better understand why SE (Systems Engineering) is important, let's look back at its history. Knowing its actual history will allow for a deeper and more enjoyable understanding of its effects, so let's take a quick look.

1940s: Development from logistics and supply chain management (WWII)

The origins of SE lie in logistics and operations research during World War II.

During World War II, it was necessary to efficiently distribute vast amounts of supplies and troops across multiple fronts (such as the European, Pacific, and African theaters).

To address the question of how to optimize an entire operation by allocating limited transport ships, supply lines, fuel, and ammunition, operations research, using mathematical and statistical methods, has developed.
* Operations Research has a proven track record in optimizing British anti-submarine warfare operations.

This logistics management required the following systems thinking:

This is the concept of "taking a bird's-eye view of the entire system and managing the relationships between its elements," which later became the foundation of systems engineering.
*Personally, I believe that Japan's biggest weakness in logistical matters during World War II is precisely why learning from it is a top priority for Japan today.

Late 1940s: Application to technological systems

After the war, the systems thinking skills cultivated in logistics began to be applied to large-scale technology projects.

These required integrating multiple technical fields, and a single expert could not grasp the whole picture, thus necessitating a systematic management approach.

1960s: Success of the Apollo program

SE established a systematic methodology,アポロ計画(1961-1972).

The Apollo program was one of the most complex projects in human history (and one of the largest in human history even by modern standards).

Successfully completing a project of this scale would have been impossible with a traditional, "craftsman-based approach." 40 people couldn't possibly function on a whim. 2 companies couldn't possibly cooperate with perfect understanding.

Therefore, NASA established systems thinking, which it had developed from WWII, as SE (Systems Engineering), and actually implemented it in the Apollo program (in reality, it took 11 years of the project to build up SE).

First, in requirements management, we broke down the top-level requirement, "moon landing and safe return," into thousands of detailed requirements, and ensured traceability for all of them.

Instead of just "going to the moon for some reason," they created a clear path: "If we fulfill these requirements, we can go to the moon."

Next, we considered what was needed to meet that requirement. We meticulously defined what elements were necessary to go to the moon and return, and that solidified the overall system concept for the Apollo program.

However, it is impossible to develop this massive system as a single unit. 40 people cannot function as one cohesive unit.

Therefore, we broke down the entire system into manageable units. We clearly defined each subsystem and clarified its scope of responsibility.

With this, the rocket team was assigned the role of "launching into space," the command module team the role of "movement in space and return," and the lunar module team the role of "landing on the moon."

However, simply disassembling the system isn't the end of the story. These systems don't operate independently; they need to connect with each other, exchange data, and work together.

Therefore, we strictly defined and thoroughly managed the connections between each system (physical, electrical signals, communication, data, etc.). The idea of ​​"we can just adjust it later" was absolutely unacceptable.

Furthermore, risks are inevitable in such massive projects. We continuously evaluated technical risks, schedule risks, and cost risks. Following the tragic loss of Apollo 1 due to the fire, we have completely reviewed our safety requirements. Learning from failures and improving the system is also a crucial element of systems engineering.

Finally, we performed verification and validation. We developed test plans at each level and confirmed the overall functionality through system integration testing.

As a result, the Apollo program successfully achieved the first human landing on the moon on July 20, 1969 (which remains one of the greatest achievements in human history).

this is,A historic success that proved the effectiveness of the SE method.Since then, SE has become a standard method in all fields in the United States, including the private sector, military, and government (currently, SE is the standard approach for governments and companies in the G7 countries other than Japan).

The structure of this series and the NASA Handbook

Now that you understand the importance of SE (Systems Engineer), let me explain how we will be discussing SE in this series.

In this series,NASA Systems Engineering Handbook (NASA/SP-2016-6105 Rev2)Based on a comprehensive translation, I will introduce the material by adding explanations, diagrams, and tables based on my own experiences.

This NASA Systems Engineering Handbook condenses the wealth of experience gained from successfully completing numerous extremely complex and unacceptable projects since the Apollo program (of course, there are also examples of failures, but the lessons learned from those are also systematically documented).

Since NASA was the one that defined and systematized SE (Systematic Engineering) during the Apollo program, I believe it is the very core document of SE itself.

When I actually worked as a systems engineer, the most important textbook I used was this "NASA Systems Engineering Handbook."

However, the one and only major weakness of this NASA Systems Engineering Handbook is that it is only available in English (which is understandable, given that it's a US government agency).

In 2026, with the increase in the number of people who can read English and the development of various tools, the barrier to accessing English-only materials is not as high as it once was. However, considering situations where you want to look something up immediately on-site, concentrate on learning, or not share it with colleagues, I've always thought that having materials written in simple Japanese would be extremely useful, so I'll actually start doing that from next time (I find reading in English 2-3 times more tiring than reading in Japanese).
*If you intend to use it as a dictionary, Japanese is more convenient.

Furthermore, since I have this opportunity to translate and post it on the site, I would like to add my own interpretations and metaphors based on my experience, as well as diagrams and tables to make it easier to understand.

Summary

Hopefully, you now have a basic understanding of systems engineering and its potential.

I believe that once you understand the basics of systems engineering, you will realize that it is a method that can be applied to a wide range of fields, not just the narrow scope of IT.
*This may sound repetitive, but the term "system" has a much broader meaning than what is typically used in Japan.

This is a technique that was actually honed in massive national projects such as World War II and the Apollo program.

Even as of 2026, it remains a fundamental way of thinking and methodology for governments and businesses in the G7 developed countries, excluding Japan. This is particularly evident in the military field, where all military operations and the development and operation of the latest stealth fighter jets such as the F-35 are essentially systems engineering in themselves.

Furthermore, SE is not merely a development methodology.

For example, when looking at government policies, you can consider questions like, "Are the requirements of this policy clear? Is there coordination between the various ministries and agencies?" When you see news reports about corporate scandals, you can consider questions like, "Is this a problem with a specific part of the system, or is it a failure of system integration?"

When we hear about development delays or project failures in the news, if we take a systems engineer's perspective, we can see the underlying problems: were the requirements too vague? Was the management of the interactions between the various elements inadequate?

And most importantly, you can apply this to your own work and life. Instead of just optimizing your own assigned tasks, thinking about overall optimization, clarifying interactions with stakeholders, and identifying risks early—these are the very principles of a systems engineer's mindset.

In this series, we will learn about SE (Systems Engineering) in a practical way using the NASA Handbook as a textbook.

Next time, we'll finally get into the main story.

Appendix: About MBSE (Model-Based Systems Engineering)

In this series, we will be using diagrams from MBSE (Model-Based Systems Engineering) to explain SE.

MBSE is a methodology that uses models (diagrams and diagrams) to represent and manage system requirements, design, and verification.

The NASA Handbook is text-based and very systematic, but understanding the structure and relationships of complex systems through text alone takes time. Therefore, we're going to make full use of MBSE, which allows for more intuitive understanding.

Therefore, in this series, we will visualize the contents of the NASA Handbook using MBSE diagrams and explain them in an easy-to-understand way. *The detailed concepts of MBSE will be explained as needed in the main text, but for now, it is sufficient to understand that it is a method of representing SE with diagrams.

• Systems Engineering Handbook, Keio University Press, supervised by Hidekazu Nishimura
  We'll be working hard to supervise the NASA handbook on this site, but it will take time, so if you want to learn the whole thing right away, I recommend this book. I own a copy myself.