

What is Event Storming?
Before getting into details, let’s discuss EventStorming’s role in an agile context. Event Storming has become a very popular methodology during the past years and has found its place in the software development lifecycle as a requirements gathering technique.

Created by Alberto Brandolini in 2012 as an alternative to precise UML diagramming, Event Storming is a workshop-style technique that brings project stakeholders together (both developers and non-technical users) to explore complex business domains in domain-driven design architecture.
One of the strengths of Event Storming is being able to focus on the business stakeholders and the high level of interaction. The technique is straightforward and requires no technical training at all.
Using Event Storming, there are different goals you can pursue:
- identify improvement areas of an existing business flow;
- explore if a new business model is viable;
- gain insight into a shared understanding of how a business operates;
- design clean and maintainable Event-Driven software.
There are three primary levels of abstraction for Event Storming:
- Big picture: used for exploring the current understanding of the system by gathering key people with different backgrounds and creating a shared understanding.
- Process modelling: in this level, we model a single business process from start to finish, clarifying all the business rules and making sure everyone is aligned.
- Software design: in this last step, we start designing the software based on building blocks from Domain-Driven Design and a reactive programming paradigm. Each sticky note potentially turns into a software artefact during the implementation phase.
When applying Event Storming, you first need to identify the Domain Events in the problem domain on a timeline. The source of a Domain Event could be the following:
- A user interaction
- An event coming
- The result of time passing by
- The consequence of another Domain Event.
We then write this domain event down on an orange sticky note.

When all domain events are defined, the second step is to find the command that caused these domain events. Commands are written on blue notes and placed directly before the corresponding domain event. Finally, you’ll need to identify the aggregates within which commands are executed and where events happen are identified. These aggregates are written down on yellow sticky notes.
Using the System Modeler
In the past years, we have embraced Event Storming as a requirements gathering technique within ACA-IT Solutions – so much so, that it’s now an integrated part of our portfolio and how we develop software for our customers. If you’d like more details about that or want to know more about Event Storming, you can contact us here.
The System Modeler uses EventStorming as an inspiration for documenting (modelling) the events that represent business processes, configuring high-level properties associated with those events, then allowing automatic generation of Apps and Collaboration Types from the model.
A System Modeler session involves the use of five virtual sticky notes to represent:
- Event: something that happens in the business
- Reaction: responses to events
- Command: user-driven actions that produce events
- External System: systems that are external to the business
- Issue: document potential problems or unknowns about events
The System Modeler also makes use of one container:
- Bounded Context: contain notes that share a common vocabulary
Below, you can see the result of an EventStorming session in the System Modeler, representing a city’s pothole reporting and tracking system. The model represents:
- a mobile app that allows city residents to report a pothole
- creation of new database records to document reported potholes
- real-time notification of city services of new pothole reports
- enable workers to update the status of a pothole
- real-time notification to the reporting resident when the status has changed

System Modeler is a great way to bridge the gap between the requirements gathering of an event-driven application and the actual implementation. In this case, we’re doing that electronically on the canvas. Moreover, this is a collaborative environment, allowing several people to work on this model at the same time. Using the System Modeler, users can collaborate with multiple individuals not only in a given room, but across any number of geographic locations. This is an awesome way to genuinely do a sort of distributed requirements gathering session. Even more so with the pandemic still preventing lots of people from going into the office!
From requirements to superfast POCs
Based on this requirements gathering session, we can now take this requirements model and create an application. All users need to do is switch from ‘model mode’ to ‘generate mode’ and group the various elements. After having defined topics and collaboration tasks, you just click on the Generate button. This simple action alone generates about 70% of this particular application’s code! This makes System Modeler probably the easiest way to very quickly move from application requirements design into application development itself.
Conclusion
Modern applications need to operate in real-time as they will be driven by what’s happening at that time in the real world. They’ll need to easily incorporate artificial intelligence and IoT technology, and the applications themselves will need to be distributed at the source of the events. The software logic will need to be able to run everywhere (cloud, edge, on-premises). These applications will also require integrating human-beings in the process for when a higher level of intuition and reasoning is needed. With System Modeler, it’s easy to quickly generate a very large portion of such an application. After all, the System Modeler has the ability to gather requirements from business users, domain experts, and developers and very quickly turn those requirements into a running event-driven application. Creating these superfast POCs is a breeze!
If you want to learn more about how ACA Group and event-driven technology can help accelerate your digital transformation, please contact us!
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In software development, assumptions can have a serious impact and we should always be on the look-out. In this blog post, we talk about how to deal with assumptions when developing software. Imagine…you’ve been driving to a certain place A place you have been driving to every day for the last 5 years, taking the same route, passing the same abandoned street, where you’ve never seen another car. Gradually you start feeling familiar with this route and you assume that as always you will be the only car on this road. But then at a given moment in time, a car pops up right in front of you… there had been a side street all this time, but you had never noticed it, or maybe forgot all about it. You hit the brakes and fortunately come to a stop just in time. Assumption nearly killed you. Fortunately in our job, the assumptions we make are never as hazardous to our lives as the assumptions we make in traffic. Nevertheless, assumptions can have a serious impact and we should always be on the look-out. Imagine… you create websites Your latest client is looking for a new site for his retirement home because his current site is outdated and not that fancy. So you build a Fancy new website based on the assumption that Fancy means : modern design, social features, dynamic content. The site is not the success he had anticipated … strange … you have build exactly what your client wants. But did you build what the visitors of the site want? The average user is between 50 – 65 years old, looking for a new home for their mom and dad. They are not digital natives and may not feel at home surfing on a fancy, dynamic website filled with twitter feeds and social buttons. All they want is to have a good impression of the retirement home and to get reassurance of the fact that they will take good care of their parents. The more experienced you’ll get, the harder you will have to watch out not to make assumptions and to double-check with your client AND the target audience . Another well known peril of experience is “ the curse of knowledge “. Although it sounds like the next Pirates of the Caribbean sequel, the curse of knowledge is a cognitive bias that overpowers almost everyone with expert knowledge in a specific sector. It means better-informed parties find it extremely difficult to think about problems from the perspective of lesser-informed parties. You might wonder why economists don’t always succeed in making the correct stock-exchange predictions. Everyone with some cash to spare can buy shares. You don’t need to be an expert or even understand about economics. And that’s the major reason why economists are often wrong. Because they have expert knowledge, they can’t see past this expertise and have trouble imagining how lesser informed people will react to changes in the market. The same goes for IT. That’s why we always have to keep an eye out, we don’t stop putting ourselves in the shoes of our clients. Gaining insight in their experience and point of view is key in creating the perfect solution for the end user. So how do we tackle assumptions …? I would like to say “Simple” and give you a wonderful oneliner … but as usual … simple is never the correct answer. To manage the urge to switch to auto-pilot and let the Curse of Knowledge kick in, we’ve developed a methodology based on several Agile principles which forces us to involve our end user in every phase of the project, starting when our clients are thinking about a project, but haven’t defined the solution yet. And ending … well actually never. The end user will gain new insights, working with your solution, which may lead to new improvements. In the waterfall methodology at the start of a project an analysis is made upfront by a business analist. Sometimes the user is involved of this upfront analysis, but this is not always the case. Then a conclave of developers create something in solitude and after the white smoke … user acceptance testing (UAT) starts. It must be painful for them to realise after these tests that the product they carefully crafted isn’t the solution the users expected it to be. It’s too late to make vigorous changes without needing much more time and budget. An Agile project methodology will take you a long way. By releasing testable versions every 2 to 3 weeks, users can gradually test functionality and give their feedback during development of the project. This approach will incorporate the user’s insights, gained throughout the project and will guarantee a better match between the needs of the user and the solution you create for their needs. Agile practitioners are advocating ‘continuous deployment’; a practice where newly developed features will be deployed immediately to a production environment instead of in batches every 2 to 3 weeks. This enables us to validate the system (and in essence its assumptions) in the wild, gain valuable feedback from real users, and run targeted experiments to validate which approach works best. Combining our methodology with constant user involvement will make sure you eliminate the worst assumption in IT: we know how the employees do their job and what they need … the peril of experience! Do we always eliminate assumptions? Let me make it a little more complicated: Again… imagine: you’ve been going to the same supermarket for the last 10 years, it’s pretty safe to assume that the cereal is still in the same aisle, even on the same shelf as yesterday. If you would stop assuming where the cereal is … this means you would lose a huge amount of time, browsing through the whole store. Not just once, but over and over again. The same goes for our job. If we would do our job without relying on our experience, we would not be able to make estimations about budget and time. Every estimation is based upon assumptions. The more experienced you are, the more accurate these assumptions will become. But do they lead to good and reliable estimations? Not necessarily… Back to my driving metaphor … We take the same road to work every day. Based upon experience I can estimate it will take me 30 minutes to drive to work. But what if they’ve announced traffic jams on the radio and I haven’t heard the announcement… my estimation will not have been correct. At ACA Group, we use a set of key practices while estimating. First of all, it is a team sport. We never make estimations on our own, and although estimating is serious business, we do it while playing a game: Planning poker. Let me enlighten you; planning poker is based upon the principle that we are better at estimating in group. So we read the story (chunk of functionality) out loud, everybody takes a card (which represent an indication of complexity) and puts them face down on the table. When everybody has chosen a card, they are all flipped at once. If there are different number shown, a discussion starts on the why and how. Assumptions, that form the basis for one’s estimate surface and are discussed and validated. Another estimation round follows, and the process continues till consensus is reached. The end result; a better estimate and a thorough understanding of the assumptions surrounding the estimate. These explicit assumptions are there to be validated by our stakeholders; a great first tool to validate our understanding of the scope.So do we always eliminate assumptions? Well, that would be almost impossible, but making assumptions explicit eliminates a lot of waste. Want to know more about this Agile Estimation? Check out this book by Mike Cohn . Hey! This is a contradiction… So what about these assumptions? Should we try to avoid them? Or should we rely on them? If you assume you know everything … you will never again experience astonishment. As Aristotle already said : “It was their wonder, astonishment, that first led men to philosophize”. Well, a process that validates the assumptions made through well conducted experiments and rapid feedback has proven to yield great results. So in essence, managing your assumptions well, will produce wonderful things. Be aware though that the Curse of Knowledge is lurking around the corner waiting for an unguarded moment to take over. Interested in joining our team? Interested in meeting one of our team members? Interested in joining our team? We are always looking for new motivated professionals to join the ACA team! {% module_block module "widget_3ad3ade5-e860-4db4-8d00-d7df4f7343a4" %}{% module_attribute "buttons" is_json="true" %}{% raw %}[{"appearance":{"link_color":"light","primary_color":"primary","secondary_color":"primary","tertiary_color":"light","tertiary_icon_accent_color":"dark","tertiary_text_color":"dark","variant":"primary"},"content":{"arrow":"right","icon":{"alt":null,"height":null,"loading":"disabled","size_type":null,"src":"","width":null},"tertiary_icon":{"alt":null,"height":null,"loading":"disabled","size_type":null,"src":"","width":null},"text":"View career opportunities"},"target":{"link":{"no_follow":false,"open_in_new_tab":false,"rel":"","sponsored":false,"url":{"content_id":229022099665,"href":"https://25145356.hs-sites-eu1.com/en/jobs","href_with_scheme":null,"type":"CONTENT"},"user_generated_content":false}},"type":"normal"}]{% endraw %}{% end_module_attribute %}{% module_attribute "child_css" is_json="true" %}{% raw %}{}{% endraw %}{% end_module_attribute %}{% module_attribute "css" is_json="true" %}{% raw %}{}{% endraw %}{% end_module_attribute %}{% module_attribute "definition_id" is_json="true" %}{% raw %}null{% endraw %}{% end_module_attribute %}{% module_attribute "field_types" is_json="true" %}{% raw %}{"buttons":"group","styles":"group"}{% endraw %}{% end_module_attribute %}{% module_attribute "isJsModule" is_json="true" %}{% raw %}true{% endraw %}{% end_module_attribute %}{% module_attribute "label" is_json="true" %}{% raw %}null{% endraw %}{% end_module_attribute %}{% module_attribute "module_id" is_json="true" %}{% raw %}201493994716{% endraw %}{% end_module_attribute %}{% module_attribute "path" is_json="true" %}{% raw %}"@projects/aca-group-project/aca-group-app/components/modules/ButtonGroup"{% endraw %}{% end_module_attribute %}{% module_attribute "schema_version" is_json="true" %}{% raw %}2{% endraw %}{% end_module_attribute %}{% module_attribute "smart_objects" is_json="true" %}{% raw %}null{% endraw %}{% end_module_attribute %}{% module_attribute "smart_type" is_json="true" %}{% raw %}"NOT_SMART"{% endraw %}{% end_module_attribute %}{% module_attribute "tag" is_json="true" %}{% raw %}"module"{% endraw %}{% end_module_attribute %}{% module_attribute "type" is_json="true" %}{% raw %}"module"{% endraw %}{% end_module_attribute %}{% module_attribute "wrap_field_tag" is_json="true" %}{% raw %}"div"{% endraw %}{% end_module_attribute %}{% end_module_block %}
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ACA does a lot of projects. In the last quarter of 2017, we did a rather small project for a customer in the financial industry. The deadline for the project was at the end of November and our customer was getting anxious near the end of September. We were confident we could pull off the job on time though and decided to try out an experiment. We got the team together in one room and started mob programming . Mob what? We had read an article that explains the concept of mob programming. In short, mob programming means that the entire team sits together in one room and works on one user story at a time. One person is the ‘driver’ and does the coding for a set amount of time. When that time has passed, the keyboard switches to another team member. We tried the experiment with the following set-up: Our team was relatively small and only had 4 team members. Since the project we were working on was relatively small, we could only assing 4 people. The user stories handled were only a part of the project. Because this was en experiment, we did not want the project - as small as it was - to be mobbed completely. Hence, we chose one specific epic and implemented those user stories in the mob. We did not work on the same computer. We each had a separate laptop and checked in our code to a central versioning system instead of switching the keyboard. This wasn't really a choice we made, just something that happened. We switched every 20 minutes. The article we referred to talks about 12, but we thought that would be too short and decided to go with 20 minutes instead. Ready, set, go! We spent more than a week inside a meeting room where we could, in turn, connect our laptops to one big screen. The first day of the experiment, we designed. We stood at the whiteboard for hours deciding on the architecture of the component we were going to build. On the same day, our mob started implementing the first story. We really took off! We flew through the user story, calling out to our customer proxy when some requirements were not clear. Near the end of the day, we were exhausted. Our experiment had only just started and it was already so intense. The next days, we continued implementing the user stories. In less than a week, we had working software that we could show to our customer. While it wasn’t perfect yet and didn’t cover all requirements, our software was able to conduct a full, happy path flow after merely 3 days. Two days later, we implemented enhancements and exception cases discussed through other user stories. Only one week had passed since our customer started getting anxious and we had implemented so much we could show him already. Finishing touches Near the end of the project, we only needed to take care of some technicalities. One of those was making our newly-built software environment agnostic. If we would have finished this user story with pair programming, one pair would know all the technical details of the software. With mob programming, we did not need to showcase it to the rest of the team. The team already knew. Because we switched laptops instead of keyboards, everyone had done the setup on their own machine. Everyone knew the commands and the configuration. It was knowledge sharing at its best! Other technicalities included configuring our software correctly. This proved to be a boring task for most of the navigators. At this point, we decided the mob experiment had gone far enough. We felt that we were not supposed to do tasks like these with 4 people at the same time. At least, that’s our opinion. Right before the mob disbanded, we planned an evaluation meeting. We were excited and wanted to do this again, maybe even at a bigger scale. Our experience with mob programming The outcome of our experiment was very positive. We experienced knowledge sharing at different levels. Everyone involved knew the complete functionality of the application and we all knew the details of the implementation. We were able to quickly integrate a new team member when necessary, while still working at a steady velocity. We already mentioned that we were very excited before, during and after the experiment. This had a positive impact on our team spirit. We were all more engaged to fulfill the project. The downside was that we experienced mob programming as more exhausting. We felt worn out after a day of being together, albeit in a good way! Next steps Other colleagues noticed us in our meeting room programming on one big screen. Conversations about the experiment started. Our excitement was contagious: people were immediately interested. We started talking about doing more experiments. Maybe we could do mob programming in different teams on different projects. And so it begins… Have you ever tried mob programming? Or are you eager to try? Let’s exchange tips or tricks! We’ll be happy to hear from you!
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OutSystems: a catalyst for business innovation In today's fast-paced business landscape, organisations must embrace innovative solutions to stay ahead. There are a lot of strategic technological trends that address crucial business priorities such as digital immunity, composability, AI, platform engineering, Low-Code , and sustainability. OutSystems , the leading Low-Code development platform , has become a game-changer in supporting organisations to implement these trends efficiently and sustainably. OutSystems enhances cyber security As organisations increasingly rely on digital systems, cyber threats pose a significant risk. Additionally, digital engagement with customers, employees, and partners, plays a vital role in a company's well-being. The immunity and resilience of an organisation is now as strong and stable as its core digital systems. Any unavailability can result in a poor user experience, revenue loss, safety issues, and more. OutSystems provides a robust and secure platform that helps build digital immune systems , safeguarding against evolving cybersecurity challenges. With advanced threat detection, continuous monitoring, secure coding practices , and AI code-scanning, OutSystems ensures applications are resilient and protected. Furthermore, the platform covers most of the security aspects for project teams, enabling them to focus on delivering high value to end customers while best practices are recommended by the platform through code analysis using built-in patterns. OutSystems simplifies cloud-native infrastructure management Cloud-native architecture has emerged as a vital component for modern application development. The OutSystems Developer Cloud Platform enables teams to easily create and deploy cloud-native applications, leveraging the scalability and flexibility of cloud infrastructure through Kubernetes . It allows companies to: Optimise resource utilisation Auto-scale application runtimes Reduce operational costs Adopt sustainable practices (serverless computing, auto-scaling, …) All this without the need for prior infrastructure investment nor the deep technical knowledge required to operate it and the typical burdens associated. OutSystems: gateway to AI and automation AI and hyper-automation have become essential business tools for assisting in content creation, virtual assistants, faster coding, document analysis, and more. OutSystems empowers professional developers to be more productive by infusing AI throughout the application lifecycle. Developers benefit from AI-assisted development, natural language queries, and even Generative AI. Once ready with your development, transporting an app to the test or production environment only takes a few clicks. The platform highly automates the process and even performs all the necessary validations and dependency checks to ensure unbreakable deployments. OutSystems seamlessly integrates with AI capabilities from major cloud providers like Amazon, Azure (OpenAI), and Google, allowing project teams to leverage generative AI, machine learning, natural language processing , and computer vision . By making cutting-edge technologies more accessible, OutSystems accelerates digital transformation and creates sustainable competitive advantages. OutSystems enables composable architecture for agility Composable architecture and business apps, characterised by modular components, enable rapid adaptation to changing business needs. OutSystems embraces this trend by providing a cloud-native Low-Code platform using and supporting this type of architecture. It enables teams to easily build composable technical and business components. With the visual modelling approach of Low-Code, a vast library of customizable pre-built components and a micro-service-based application delivery model, OutSystems promotes high reusability and flexibility. This composable approach empowers organisations to: Respond rapidly to changing business needs Experiment with new ideas Create sustainable, scalable, and resilient solutions OutSystems enables the creation of business apps that can be easily integrated, replaced, or extended, supporting companies on their journey towards composability and agility. OutSystems facilitates self-service and close collaboration Platform engineering, which emphasises collaboration between development and operations teams, drives efficiency and scalability. OutSystems provides a centralised Low-Code platform embracing this concept at its core by being continuously extended with new features, tools and accelerators. Furthermore the platform facilitates the entire application development lifecycle until operations . Including features like Version control Automated deployment Continuous integration and delivery (CI/CD) Logging Monitoring Empowering organisations to adopt agile DevOps practices. With OutSystems, cross-functional teams can collaborate seamlessly, enabling faster time-to-market and improved software quality. By supporting platform engineering principles, OutSystems helps organisations achieve sustainable software delivery and operational excellence. OutSystems drives sustainability in IT OutSystems leads the way in driving sustainability in IT through its green IT Low-Code application development platform and strategic initiatives. By enabling energy-efficient development, streamlining application lifecycle management, leveraging a cloud-native infrastructure , and promoting reusability , OutSystems sets an example for the industry. Organisations can develop paperless processes, automate tasks, modernise legacy systems, and simplify IT landscapes using OutSystems 3 to 4 times faster, reducing overall costs and ecological footprint. By embracing OutSystems, companies can align their IT operations with a greener future, contribute to sustainability, and build a more resilient planet. Wrapping it up In the era of digital transformation and sustainability, OutSystems is a powerful ally for organisations, delivering essential business innovations, such as … High-performance Low-Code development Cloud-native architecture AI and automation Robust security measures Collaborative DevOps practices Take the OutSystems journey to align with IT trends, deliver exceptional results, and contribute to a sustainable and resilient future. Eager to start with OutSystems? Let us help
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Want to dive deeper into this topic?
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