How Much Blockchain Do You Need? Towards a Concept for Building Hybrid DApp Architectures (WETSEB @ ICSE 2018)

1. 1 WETSEB @ ICSE 2018 Gothenburg, Sweden 2018-05-27 Florian Wessling, Christopher Ehmke, Marc Hesenius and Volker Gruhn ﬂorian.wessling@paluno.uni-due.de University Duisburg-Essen, Germany Prof. Dr. Volker Gruhn How Much Blockchain Do You Need? Towards a Concept for Building Hybrid DApp Architectures

2. Motivation • Take advantage of Blockchain technology: decentralized, trustless, transparent and tamper-proof app environment • Deal with disadvantages: blocktime delay, technical complexity, difficult updates • Difficult to determine: • Which attributes are important for my use case? • Which elements of my architecture benefit from blockchain technology? • Increasing need to build good decentralized app (DApp) architectures • Best practices, architectural patterns, design patterns for smart contracts • Concepts to support architectural design of blockchain-based applications are missing 2

3. Current Approaches 3 • No • Yes, Public • Yes, Private Do I need a Blockchain? • Yes, 1.2 MB Blocksize, 13s Blocktime, Hybrid PoS/PoW consensus, ... • Yes, custom protocol, 9.4s Blocktime, DPoS consensus, ... Gap: Finer-grained and balanced approach!

4. • Four step approach: • 1. Identify participants • 2. Identify trust relations between participants • 3. Identify interactions between participants • 4. Derive an architectural draft • Usage • Adding blockchain technology to existing systems • Assessing use cases for implementing a new system 4 B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 1. Participants B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 2. Trust Relations B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 3. Interactions Area B Area A B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 4. Architectural Draft [2]

5. • Example use case: Coordination and payment of craftsmen constructing a building • 1. Identify participants • 2. Identify trust relations between participants • Building owner and construction supervisor trust each other • Contractors only trust supervisor as their only contact with the construction site • 3. Identify interactions between participants • Contractors report to supervisor • Supervisor reports to building owner • Building owner pays contractors • 4. Derive an architectural draft • Use of blockchain technology in Area A makes no sense • For interaction between Building Owner and Contractors using a blockchain makes sense! 5 B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 1. Participants B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 2. Trust Relations B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 3. Interactions Area B Area A B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor 4. Architectural Draft [2]

6. Outlook: Overall Concept 6 B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor Area B Area A B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor B ZY S X Contractor Construction Supervisor Building Owner Contractor Contractor Architectural Patterns + Best Practices Use Case Terms + Properties Implementation as   Smart Contract + Design Patterns

7. • Open issues • How to model trust? Different levels of trust? Depending on context? • How to model interactions? What is the right level of abstraction? Which interactions are relevant? • Clear terminology for terms is required • Validation • Small-scale study with group of 8 students (CS Master) • Build architectures within research projects (building, energy, insurance) • How to quantify the results? How to measure what a good architecture is? Future Work 7

8. 8 Thank you! 😄 Questions? 💭 Discussion? 💬