Transcript Discovering the value of Domain-Driven Design presented by
Discovering the value of Domain-Driven Design
presented by Herman Lintvelt (c) 2011 Polymorph Systems
Do the right thing, and do the thing right.
“When we first set out to write software, we never know enough.”
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What are some of the prominent problems you struggle with in your software development projects?
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When faced with these problems or complex requirements, how do you go about to resolve them?
An Experiment
In which we make use of volunteers to do some role-playing.
Scenario A
Scenario A
Scenario B
Scenario B
Scenario B
So what was the difference?
• Build up a model of the domain to enhance understanding • Based on this a common language was being developed • New understanding immediately fed into model and language
Coming to terms...
• • • • Domain: subject area to which solution must be applied • • • Domain Model: simplification of real world abstracts aspects relevant to solving problem at hand not just a particular diagram • Ubiquitous Language: everywhere the same language
What is DDD?
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DDD is both way of thinking and set of • • • priorities aimed to accelerate software dealing with complex domains primary focus on domain and domain logic complex domain designs should be based on a model Two development practices prerequisites: 1.
Development is iterative 2.
Developers and domain experts have a close relationship
Where does DDD fit?
• • DDD is not a new idea!
Central part of OO Analysis & Design Model Code Langua ge
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What are different nouns that can be used for “car”?
• • • • • • • • car vehicle bakkie automobile SUV minibus HMUV (High Mobility Utility Vehicle) jamjar (Cockney slang)
Case Study 0
• • 5.1.7 [Req-XXXX] - Car Finder Allow the end user to locate itself and the vehicle.
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Case Study 0
- ( SoapRequest *) GetLastKnownVehiclePosition: ( id < SoapDelegate >) handler uiTokenID: ( NSString *) uiTokenID vehicleRegistrationNr: ( NSString *) vehicleRegistrationNr; • • • • • • - ( SoapRequest *) UnitPlayback: ( id < SoapDelegate >) handler uiTokenID: ( NSString *) uiTokenID dtStartDate: ( NSDate *) dtStartDate dtEndDate: ( NSDate *) dtEndDate liCustomerVehicleID: ( long ) liCustomerVehicleID;
Case Study 0
Case Study 1
• As a user of the XXXX iphone application • I want to view my current location and my car’s location on a map, with the shortest route indicated visually • So that I can easily find my car
Case Study 1
Case Study 1
Case Study 1
• • • • • • The direct benefits we gained in project: • Simpler code better separation in layers • Faster development requirements, code & tests could be verified against domain model • easier to debug & refactor in domain layer than in UI, Persistence, Web-service layers Focused on correct user stories Better tested Team interaction & communication improved dramatically
Utility of a Model
• In DDD, the Model has 3 basic uses: 1.
The model and the heart of the design • shape each other makes model relevant, ensures the analysis applies to final product 2.
The model is a backbone of a language used by all team members 3.
• The model is distilled knowledge team’s agreed way of structuring domain knowledge and key domain elements
DDD and DSLs
• DSL “allows solutions to be expressed more clearly and closer to the domain” • • Model can be expressed as DSL Model • • • DSL can be used to generate scaffolding code Code generate specification and test docs define business (domain) rules Langu age
1.
Ingredients of Effective Modeling
Binding the model and the implementation 2.
• Cultivating a language based on the model can also include technical terms to be taught to domain experts 3.
• Developing a knowledge-rich model Objects not just data scheme (anemic objects), but has behaviour and enforce rules 4.
Distilling the model 5.
• Brainstorming and experimenting Agile modeling, Model out Loud
Deep Domain Model
• • • When faced with complexity, do you deepen your domain knowledge OR deepen your technology stack?
Sad Example
• Client: “Our system is very expensive to maintain, and performance is horrible” • Me: “Why do you think?” • Client: “Well, cause we’re using Java and it is really slow and has a high learning curve” • Me: “Interesting. Tell me about the business domain of the system...” • Client: “Well, we’re integrating with a legacy system and use Java EE and added ESB to help with that....”
Modeling out Loud
• • People has a genius for spoken language Unfortunately they usually don’t use the language of domain model when speaking • We must harness linguistic ability to the modeling effort • It complements the visual/spatial reasoning done by sketching diagrams • As we model out loud, we find easier ways to say • what we need to say NB to then take those new ideas back to the diagrams and code
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Discuss what you see as benefits of DDD that applies to your current projects of software development circumstances?
What benefits will you gain if you start thinking and designing more domain focused? (short, medium, long term?)
DDD Benefits
• • Allows effective collaboration Earlier experience feed back into model and understanding of whole team • • Helps focus requirement analysis • Allows evolving of model over time “When we first set out to write software, we never know enough.”
References
• • Applying UML and Patterns, Prentice Hall - Craig Larman Domain Driven Design, Addison-Wesley - Eric Evans
If you want...
• • • • • • • contact me: [email protected]
http://www.polymorph.co.za
twitter: hermanlintvelt blog: http://blog.richclientgui.com
• training: http://jtraining.co.za
OO A&D Course, CapeTown, end of July Thank you