Assessing the Suitability of UML for Modeling Software Architectures Nenad Medvidovic Computer Science Department University of Southern California Los Angeles, CA

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

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

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

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

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

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

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

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

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

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

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

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

Strategy #1: UML Metamodeling Architecture

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)

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

Strategy #2: UML Metamodeling Architecture

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

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

Strategy #3: UML Metamodeling Architecture

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

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

From Architecture to Implementation

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

Round-Trip Software Engineering Using UML

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