Domain-Driven Transformation

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Starring Directed By Special Appearance Presented by Photo: Hackercatxxy/Wikipedia

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@hschwentner

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@hschwentner

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@hschwentner

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@hschwentner

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@hschwentner

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@hschwentner

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THE NAME OF THIS SPEAKER IS HENNING SCHWENTNER LIVE 45 MIN TALK

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!"# Kolleg:in gesucht (Deutschlandweit)

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Story Time

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@hschwentner Alphorn Auto Leasing Inc.

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@hschwentner

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@hschwentner

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Monolease A

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salesperson [person] Monolease [software system] Central car leasing tool customer [external person] risk manager [person] closes leasing contracts with creates and calculates contracts in assesses risk of contracts in Alphorn Auto Leasing Inc. [enterprise] Context

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@hschwentner Photo: Myriam Thyes/Wikipedia

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@hschwentner Photo: Keiichi Inoue/flickr

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@hschwentner long time to market error-prone teams get in each other’s way Issues with Legacy Systems it’s hard to build new ideas into the system and they are doing more or less the same there are often more than one

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@hschwentner Alphorn’s boss: “Modernize it!”

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@hschwentner Photo: Keiichi Inoue/flickr

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=> I hate this old mess! This system has earned our money for decades

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@hschwentner The consultant: “Modularize it!”

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=> modules monolith to

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=> modules monolith buy to carve out build new

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@hschwentner Diagnosis: From Which Diseases Does Our Patient suffer?

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@hschwentner Different diseases require different treatment

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@hschwentner big ball of mud poorly expressed domain knowledge bad team organization Typical Diseases of Legacy Systems

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@hschwentner big ball of mud poorly expressed domain knowledge bad team organization Cures strategic transformation tactical transformation team-organizational transformation

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@hschwentner Domain-Driven Refactorings • Strategic Refactorings • Tactical Refactorings (that support strategic ones) Catalog: https://hschwentner.io/domain-driven-refactorings strategic transformation tactical transformation team-organizational transformation • Socio-Technical • Tactical refactorings (that strengthen domain knowledge in the code)

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@hschwentner Strategic

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@hschwentner Strategic Transformation 1. Step: Domain re-discovery 2. Step: Modeling the target architecture 3. Step: Aligning current with target architecture 4. Step: Do the move

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@hschwentner Strategic Transformation 1. Step: Domain re-discovery 2. Step: Modeling the target architecture 3. Step: Aligning current with target architecture 4. Step: Do the move

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@hschwentner Step 1: Domain Re-Discovery

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@hschwentner To modernize the legacy system we ﬁrst have to put it aside

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@hschwentner To split the monolith we ﬁrst have to put it aside

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Mindset Switch

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thinking about business => thinking about technology to

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! ! " have to understand To build software: Tech people business people. # "

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! ! " # " Tech people business people. common understanding

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! ! " # " Tech people business people. common language

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! ! " # " Tech people business people. ubiquitous language

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=> direct communication telephone game to user dev user dev

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Collaborative Modeling

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Collaborative Modeling

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customer tells wish for 1 salesperson signs to gives for contract 3 risk manager contract passes on to 4 contract votes checks calculates 5 6 7 calculates to 8 2 car credit rating installment car resale value contract

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https://hschwentner.io Read on in:

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May 7th—10th 2025 Vienna, Austria The Collaborative Modeling Unconference comocamp.org Event Storming User Story Mapping Event Modeling Impact Mapping Domain Storytelling Storystorming Context Mapping Example Mapping etc.

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@hschwentner Step 2: Determining the Target Architecture

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Drawing Boundaries

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Which activities belong together (from an actor’s perspective)?

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@hschwentner sales risk assessment Context Map

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@hschwentner Step 3: Aligning Current Architecture with Target Architeture

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@hschwentner Aligning Current and Target Architecture current target

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@hschwentner Determining the Current Architecture analysis tool developers architecture analyst source code

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https://sustainable-software- architecture.com Read on in: analysis tool architecture analyst

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Monolease [software system] salesperson [person] Monolease [software system] Central car leasing tool customer [external person] risk manager [person] closes leasing contracts with creates and calculates contracts in assesses risk of contracts in Alphorn Auto Leasing Inc. [enterprise] Context again

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backend [container] database [container] frontend [container] salesperson [person] backend [container: EJB 2] risk manager [person] creates and calculates contracts in assesses risk of contracts in Monolease [software system] frontend [container: servlets, JSPs] database [container: IBM DB2] Containers

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Calculator [component] frontend [container] LeasingServlet [component: servlet] CONTRACTS [database table] PartnerServlet [component: servlet] ContractService [component] PartnerService [component] backend [container] database [container] Contract [component] Partner [component] PARTNERS [database table] Components

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big ball of mud => no vertical structuring

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@hschwentner Aligning Current and Target Architecture current target

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Calculator [component] ContractService [component] PartnerService [component] backend [container] Contract [component] Partner [component] Component Backend

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Component Bounded Contexts Sales Risk assessment

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Calculator [component] ContractService [component] PartnerService [component] Contract [component] Partner [component] Component Bounded Contexts Sales Risk Assessment

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Calculator [component] ContractService [component] PartnerService [component] Contract [component] Partner [component] Sales Risk Assessment Contract [component] Partner [component] Duplication?

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@hschwentner Dave Thomas The DRY Principle Andy Hunt “Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.”

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ContractService [component] Contract [component] Component Backend Sales Risk assessment

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ContractService signContract() voteContract() Code Contract getContractNumber() setSignatureDate() setCreditRating() setVotingResult()

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ContractService signContract() voteContract() Code Contract getContractNumber() setSignatureDate() setCreditRating() setVotingResult() Sales Risk Assessment

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ContractService signContract() voteContract() Code Contract getContractNumber() setSignatureDate() setCreditRating() setVotingResult() Sales Risk Assessment ContractService signContract() voteContract() Contract getContractNumber() setSignatureDate() setCreditRating() setVotingResult()

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ContractService signContract() Code Contract getContractNumber() setSignatureDate() Sales Risk Assessment ContractService voteContract() Contract getContractNumber() setCreditRating() setVotingResult()

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ContractService signContract() Contract getContractNumber() setSignatureDate() Sales Risk Assessment ContractService voteContract() Contract getContractNumber() setCreditRating() setVotingResult() ContractService signContract() voteContract() Contract getContractNumber() setSignatureDate() setCreditRating() setVotingResult() Monolease =>

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@hschwentner Improvement Backlog 1.2 Extract Specialized “Contract Service” 1.1 Extract Specialized “Contract” 1 Extract Context “Sales” Collecting Refactorings 2 Extract Context “Risk assessment” 2.1 Extract Specialized “Contract Service” 2.1 Extract Specialized “Contract”

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@hschwentner Step 4: Do the Move

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@hschwentner Improvement Backlog Planning Transformation Tactical Refactoring 1.1 Strategic Refactoring 1 User Story A Product Backlog User Story E User Story B User Story C User Story D Tactical Refactoring 1.2 Tactical Refactoring 1.3 Tactical Refactoring 2.1 Strategic Refactoring 2 Sprint Backlog

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@hschwentner Improvement Backlog Planning Transformation User Story A Product Backlog User Story E User Story B User Story C User Story D Sprint Backlog Tactical Refactoring 1.1 Strategic Refactoring 1 Tactical Refactoring 1.2 Tactical Refactoring 1.3 Tactical Refactoring 2.1 Strategic Refactoring 2

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@hschwentner Improvement Backlog Planning Transformation Strategic Refactoring 1 Product Backlog User Story E User Story C User Story D Tactical Refactoring 1.3 Tactical Refactoring 2.1 Strategic Refactoring 2 Sprint Backlog

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@hschwentner Improvement Backlog Planning Transformation Strategic Refactoring 1 Product Backlog User Story E User Story C User Story D Tactical Refactoring 2.1 Strategic Refactoring 2 Sprint Backlog User Story F User Story G Tactical Refactoring 1.3

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@hschwentner Improvement Backlog Planning Transformation Product Backlog User Story E Tactical Refactoring 2.1 Strategic Refactoring 2 Sprint Backlog User Story F User Story G

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@hschwentner Improvement Backlog Planning Transformation Product Backlog User Story E Tactical Refactoring 2.1 Strategic Refactoring 2 Sprint Backlog User Story G User Story H User Story F User Story I

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ContractService signContract() voteContract() Code Contract getContractNumber() setSignatureDate() setCreditRating() setVotingResult() Risk Assessment ContractService Contract Monolease voteContract() getContractNumber() setCreditRating() setVotingResult()

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ContractService signContract() Code Contract getContractNumber() setSignatureDate() Risk Assessment ContractService Contract Monolease voteContract() getContractNumber() setCreditRating() setVotingResult()

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@hschwentner Tactical

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Code Risk Assessment ContractService voteContract() Contract getContractNumber() setCreditRating() setVotingResult() anemic

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@hschwentner Team- Organizational

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@hschwentner sales risk assessment A Context Belongs to a Team Exclusively team A team B

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@hschwentner Outlook

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@hschwentner What Else? Socio-technical transformation Technical transformation Tactical transformation Anti-Anemia refactorings

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@hschwentner Domain Patterns Pipeline Domain Blackboard Domain Dialog Domain • Logistics • Insurances and banks • administration • healthcare • event management • control center • Software development • Communication software • Negotiations in various domains

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@hschwentner Conclusion

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https://hschwentner.io Read on in: https://hschwentner.io/domain-driven-refactorings

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Lesson: is possible Monolith transformation (and hard) =>

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@hschwentner Mistake: Going on the journey alone Better:

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Photo: Henning Schwentner

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! ❤

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@hschwentner

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Bibliography Conway, Melvin E. “How Do Committees Invent?” Datamation 14, no. 5 (April 1968): 28–31. Evans, Eric. Domain-Driven Design: Tackling Complexity in the Heart of Software. Boston: Addison- Wesley, 2004. Feathers, Michael C. Working Effectively with Legacy Code. Upper Saddle River, NJ: Prentice Hall, 2004. Foote, Brian and Joseph Yoder. “Big Ball of Mud.” PLoP ’97, Monticello, IL, September 1997. Fowler, Martin. “Strangler Fig Application.” Bliki, June 29, 2004. Fowler, Martin. Refactoring: Improving the Design of Existing Code. 2nd ed. Boston: Addison-Wesley, 2019. Hofer, Stefan and Henning Schwentner. Domain Storytelling: a Collaborative, Visual, and Agile Way to Develop Domain-Driven Software. Boston: Addison-Wesley, 2022. Lilienthal, Carola. Sustainable Software Architecture: Analyze and Reduce Technical Dept. Heidelberg: dpunkt, 2019. Lilienthal, Carola and Henning Schwentner. Domain-Driven Transformation: Modularize and Modernize Legacy Software. Boston: Addison-Wesley, 2025. Kernighan, Brian W. Software Tools in Pascal. Addison-Wesley, 1981. Newman, Sam. Monolith to Microservices: Evolutionary Patterns to Transform Your Monolith.

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Henning Schwentner  https://hschwentner.io  in/henningschwentner ✉ [email protected] Kolleg:in gesucht (Deutschlandweit)