@kenny_baas @[email protected] How domain-​ driven design enabled scaling a big ball of mud product Photo by National Cancer Institute

@kenny_baas @[email protected] Agenda Once upon a time..... Domain-​ Driven Design 101 Why understanding the underlying needs of users was crucial Collaborative software design and embedding software architecture in the team From output to data-​ driven outcomes through Domain-​ Driven Design

@kenny_baas @[email protected] Legend user (external) needs user (internal) Capabilities * Simplified map - left out accepting, screening and billing and more... Companies with blue collar workers temporary employees for blue collar jobs Students age 18-25 Temporary jobs able to work next to studying Looking for a job online website job openings database Customer agreements Job openings Pay Custom ERP Recruiter Fulfil jobs for customer Email Applying for job account management account management

@kenny_baas @[email protected] * Simplified map - left out accepting, screening and billing and more... Legend user (external) needs user (internal) Capabilities Companies with blue collar workers temporary employees for blue collar jobs Students age 18-25 Temporary jobs able to work next to studying Looking for a job online website job openings database Customer agreements Job openings Pay Custom ERP Recruiter Fulfil jobs for customer Email Applying for job account management account management ERP Payrolling payout student

@kenny_baas @[email protected] * Simplified map - left out accepting, screening and billing and more... Student 18-25 years Work single day job when money is needed Company Find blue collars worker 'last minute' Legend user (external) needs user (internal) Capabilities Companies with blue collar workers temporary employees for blue collar jobs Students age 18-25 Temporary jobs able to work next to studying Looking for a job online website job openings database Customer agreements Job openings Pay Custom ERP Recruiter Fulfil jobs for customer Email Applying for job account management account management ERP Payrolling payout student

@kenny_baas @[email protected] Hyper flex Written in ruby on Rails over 1.5 year time from scratch Based on previous models from the website Uses both the website, custom ERP and SaaS ERP Reusable capabilities for FLEX to automate manual processes Looks promising and strategy is to also go live in another country Scaled up from 3 to 13 engineers, hybrid working Keep delivering new features Photo by Osman Rana on Unsplash

@kenny_baas @[email protected] It is designed to make programming web applications easier by making assumptions about what every developer needs to get started. It allows you to write less code while accomplishing more than many other languages and frameworks. Rails emphasizes the use of convention over configuration (CoC) and follows the principle of Don't Repeat Yourself (DRY).

@kenny_baas @[email protected] The Model is usually the boundary, where new features are being added to...Ending up with a Big Ball of Mud

@kenny_baas @[email protected] Team A Team B Application Database Somewhere around the Millenium Domain-​ Driven Design 101

@kenny_baas @[email protected] Domain models often start based on a naïve, over simplified entity-​ relationship model based on reality. Good when you start, but when dealing with more complicated and complex problems it will become a big ball of mud

@kenny_baas @[email protected] Platonic Domain model thinking assumes idealized, abstract representations of reality which may not always capture the intricacies of a domain. This can be misleading in Domain-​ Driven Design (DDD), especially in core or complicated supporting domains where the nuances matter. A naïve model, influenced by this thinking, can confine you to an oversimplified view, potentially leading to incorrect, suboptimal and unadaptable software solutions. Inspired by Barry M O'Reilly - Plato is the devil Anti-​ Pattern: Platonic Domain Model Thinking

@kenny_baas @[email protected] Users and stakeholders Other people involved in designing and building software Managers Architects User researcher Analysts ..... Code Engineering Team

@kenny_baas @[email protected] Photo by pure julia on Unsplash For each specific problem, a different map For each specific problem, a different model

@kenny_baas @[email protected] Job template Jobs Jobs Applications Candidate applications Application Job drafting Job Fulfilment Candidate applications

@kenny_baas @[email protected] Job template Jobs Jobs Applications Candidate applications Application ...... Domain-​ Driven Design allows you to break down your domain into smaller models, enabling a single team to take ownership, even within a monolithic architecture. This empowers the team to make changes more independently, as it reduces the impact of those changes on other models. Job drafting Job Fulfilment Candidate applications

@kenny_baas @[email protected] Photo by oxana v on Unsplash Keep the shop open: Start extracting bounded context guided by the roadmap What bounded context do we touch that is on the backlog? What is something on the backlog what is hard to do with the current model?

@kenny_baas @[email protected] Building a shared understanding of your domain and use it to guide your design _is_ the philosophy behind DDD. The rest is principles, patterns, and practices. — Mathias Verraes Domain-​ Driven Design 101 - Summary

@kenny_baas @[email protected] Why understanding the underlying needs of users was crucial Photo by Kelly Sikkema on Unsplash

@kenny_baas @[email protected] Onboarding a student Signup for an account Screen a candidate Upload compliancy information and documents Plan a kickstart Check student compliancy Enable on platform Student 18-25 years Work single day job when money is needed Recruiter Find the best job for a student to work on apply for a job user (external) needs user (internal) Capabilities Account service Kickstart service Screening service Compliancy service Candidate service

@kenny_baas @[email protected] Anti-​ Pattern: Splitting a big ball of mud based on objects or process Refactoring a monolithic system by dividing it based on abstract or "platonic" object concepts can lead to a fragmented architecture, an approach that's an acknowledged anti-​ pattern. This method, focused on idealized object categories rather than concrete functionalities, often results in ambiguous module responsibilities, impractical implementations, increased maintenance overhead, and reduced adaptability to new requirements. Inspired by Barry M O'Reilly - Plato is the devil

@kenny_baas @[email protected] https://medium.com/inclusive-​ software/when-​ why-​ to-​ explore-​ the-​ problem-​ space-​ 16068f1a1dbc

@kenny_baas @[email protected] Collaborative modelling is a visualisation technique to analyse complex and conflict-​ laden decision-​ making processes with all relevant stakeholders and decision-​ makers to create a shared understanding.

@kenny_baas @[email protected] https://www.eventstorming.com/ First time we started with only the team, on-​ site. Afterward we move it to a miro board, so we could continue online. EventStorming became the default modelling language to design software for the engineers. Once the engineers had a good understanding of EventStorming, we started doing session with stakeholders 1. 2. 3. 4.

@kenny_baas @[email protected] ........ ........ ........ ........ ........ ........ ........ Start with 1 Miro board, and let the team self organise and enable structuring by splitting the miro board when needed. Giving each bounded context it's own board * Note, the team themselves decided on using miro

@kenny_baas @[email protected] Prepare templates before doing collaborative modelling with certain key stakeholder

@kenny_baas @[email protected] Distilling Bounded Context Onboarding a student Signup for an account Screen a candidate Upload compliancy information and documents Plan a kickstart Check student compliancy Enable on platform Student 18-25 years Work single day job when money is needed Recruiter Find the best job for a student to work on apply for a job user (external) needs user (internal) Capabilities Candidate screening Candidate compliancy Candidate management Account management Split according to the: Language Departments Users And run through the design with scenarios 1. 2. 3.

@kenny_baas @[email protected] Photo by Trnava University on Unsplash Start applying Domain-​ Driven Design on a complicated, medium risk problem. That way the team can experiment with the new patterns safely, and get used too the paradigm shift without to much risk and organisation exposure

@kenny_baas @[email protected] Understanding the user needs - summary We are so caught up in the solution space that we miss perspectives that we forget to understand that we miss opportunities  ​  ​  ​  ​  ​  ​ — Indi Young CC BY-​ SA: INDI YOUNG

@kenny_baas @[email protected] Embedding software architecture in the team

@kenny_baas @[email protected] A paradigm shift Command Bounded Context Entity Domain Event Event Handler Command Bounded Context Entity Domain Event Controllers (MVC or Rest)

@kenny_baas @[email protected] Photo by Nima Mot on Unsplash "Pair programming is not just about writing code together; it's about weaving two minds into a singular thread of creativity and problem-​ solving."

@kenny_baas @[email protected] Controllers (MVC or Rest) Rest request (command) Rest request (query) Company management Command Services Aggregate Company Registered WorkLoc ationUp dated Legacy model Rest request (query) Event Handler Do something else Database Entity table Column Column Column Updates Views Entity Reads request (command) request (query) Bubble context Controllers (MVC or Rest) Rest request (command) Rest request (query) Company management Command Services Aggregate Company Registered WorkLoc ationUp dated Legacy model Rest request (query) Event Handler Database Aggregate table Column Column Column Views Entity Reads Read entity Table Updates Column Column Column Event Handler Do something else request (command) request (query) Autonomous Bubble context

@kenny_baas @[email protected] https://bytesizearchitecturesessions.com/ Andrea Magnorsky Bytesize architecture session

@kenny_baas @[email protected]

@kenny_baas @[email protected] Sustainable design decisions are decisions that consider the sociotechnical impact of the alternatives. After designing and analysing the alternatives, you pick the one that gives you the best sociotechnical trade-​ off with the information that is available. You create a feedback loop into your design process to improve it along the way. Over time, you will find yourself making decisions in a similar way. This is when your decisions become sustainable. Collaborative software design - summary Sociotechnical System - from https://www.researchgate.net/figure/Sociotechnical-​ system-​ STS-​ 4_fig2_306242078

@kenny_baas @[email protected] Photo by Ibrahim Boran on Unsplash From output to data-​ driven outcomes through Domain-​ Driven Design

@kenny_baas @[email protected] Job Drafting Add job Job Added Job Fullfiment Publish Job Job Published Cancel job Apply candidate for job Cancel application Job Cancelled Candidate applied for job Application cancelled ACL Create legacy Job Legacy model Create job Job Created Challenging the backlog....

@kenny_baas @[email protected] Business monitoring

@kenny_baas @[email protected] “We can't impose our will on a system. We can listen to what the system tells us, and discover how its properties and our values can work together to bring forth something much better than could ever be produced by our will alone.”  ​  ​  ​  ​  ​ — Donella H. Meadows From output to data-​ driven outcomes through Domain-​ Driven Design - Summary

@kenny_baas @[email protected]

@kenny_baas @[email protected]

@kenny_baas @[email protected] Thank You #CatTax kenny@weave-​ it.org - weave-​ it.org Get the book here