1. Assessing the Suitability of UML for Modeling Software Architectures Nenad Medvidovic Computer Science Department University of Southern California Los Angeles, CA 90089-0781 neno@usc.edu http://sunset.usc.edu/~neno/

2. Outline 4 Overview of software architectures 4 Overview of UML 4 Modeling software architectures in UML 4 Lessons learned 4 Current status 4 Conclusions

3. Software Architectures 4 High-level model of a software system –software components –their interactions – software connectors –their interconnections – configurations 4 Promise of software architectures –better, more reliable software systems –modeling important system aspects early –ensuring system properties throughout

4. Key Architectural Concepts 4 Components – loci of computation and state 4 Connectors – loci of interaction –communication –coordination –mediation 4 Architectural constraints –structural vs. behavioral –local vs. non-local vs. global 4 Architectural style + –interaction constraints + topological constraints

5. Example Architecture 4 Components interact via connectors 4 Connectors enforce interaction constraints 4 Configurations reflect topological constraints

6. Architecture Description Languages 4 High-level architecture modeling notations 4 Model architectural structure and behavior 4 Difference in focus 4 Varying degrees of formality 4 Varying levels of tool support 4 Differences in maturity

7. Example ADLs 4 C2 –focus on style-based topological constraints and evolution –static component behavior in 1st order logic 4 Wright –focus on connectors –dynamic subsystem behavior in CSP 4 Rapide –focus on system events –dynamic system behavior using event patterns and posets

8. Unified Modeling Language: Motivation 4 Community fragmentation Academic Approach to Architectures Industrial Approach to Architectures Focus on wide range of development issues Focus on analytic evaluation of architectural models Families of modelsIndividual models Practicality over rigorRigorous modeling notations Architecture as the “big picture” in development Powerful analysis techniques Breadth over depthDepth over breadth General-purpose solutionsSpecial-purpose solutions

9. 4 Provides an economy of scale –more and better tools –improved tool interoperability –more skilled developers –lower training costs 4 Combine the benefits of powerful, specialized notations with those of widely adopted, general notations –specific solution: “integrate” ADLs with UML Unified Modeling Language: Standardization

10. Unified Modeling Language: Benefits 4 Large, useful set of predefined constructs 4 Extensible 4 Semi-formal definition of syntax and semantics via –a meta model –descriptive text –constraints 4 Potential for –wide adoption –standardization –substantial tool support 4 Basis in experience with mainstream development methods

11. Unified Modeling Language: Extensibility 4 New constructs may be added to address new development issues 4 Three extensibility mechanisms – constraints – tagged values – stereotypes Stereotype Person for instances of meta class Class [1] A Person can be either female or male personGender : enum { female, male } 4 The meta model may also be extended – results in a new notation – may be incompatible with UML-compliant tools

12. Modeling Software Architectures in UML 4 Strategy #1 –use UML “as is” –enables direct comparison of UML and an ADL 4 Strategy #2 –use UML’s built-in extension mechanisms –allows automated conformance checking to architectural style rules 4 Strategy #3 –augment the UML meta model to directly support architectural concerns

13. Strategy #1: Using UML “As Is” 4 Simultaneous consideration of architecture composition rules and UML notational constructs 4 Develop a UML domain model 4 Develop an (informal) architectural diagram 4 Map domain classes to architectural components 4 Design class (component) interfaces 4 Provide constructs for modeling connectors –connectors add no functionality at the domain model level 4 Model architectural structure in class and/or collaboration diagrams

14. Strategy #1: UML Metamodeling Architecture

15. Strategy #1: Example Comp3 Comp2Comp1 Conn1 C3i C2i C1i 2:Request()3:Request() c3 : Comp3 :Comp2:Comp1 1:Request() bus : Conn1 4:Notif1(data1)5:Notif2(data2) 6:Notif2(data2) 7:Notif1(data1)

16. Strategy #2: Constraining UML 4 Identify UML meta classes semantically similar to major architectural constructs –operation, message, port –component, connector, architecture 4 Define stereotypes and apply them to meta class instances –use stereotypes to model structural aspects of an architecture 4 Describe semantics using UML diagrams –sequence, statechart, collaboration, activity

17. Strategy #2: UML Metamodeling Architecture

18. Strategy #2: Example > Comp3 > Comp2 > Comp1 > Conn1 >

19. Strategy #3: Augmenting UML 4 Introduce explicit architectural constructs and constraints in UML 4 Introduce additional notations for modeling architectural semantics 4 Follow an approach similar to Strategy #1 to model specific architectures  Follow an approach similar to Strategy #2 to model specific architectural styles

20. Strategy #3: UML Metamodeling Architecture

21. Discussion of Integration Strategies 4 All three approaches have merits and shortcomings 4 “Straight” UML –understandable architectures –manipulable by standard tools –architectural constraint violations 4 “Constrained” UML –ensures architectural constraints –requires complete style specifications –requires OCL-compliant tools 4 “Extended” UML –provides “native” support for architectures –requires backward tool compatibility –may result in incompatible UML versions

22. Current Status 4 Integrated environment for transforming C2-style architectures into UML

23. From Architecture to Implementation

24. Architectural View Mismatches 4 Different UML diagrams present different system views –redundant information across views 4 Key challenge is to ensure inter-view consistency 4 Ramifications on round-trip engineering

25. Round-Trip Software Engineering Using UML

26. Conclusions 4 Software modeling philosophies 4 Assumptions 4 Problem domain modeling 4 Architectural abstractions 4 Modeling behavior 4 Architectural style 4 Architectural views