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Devnology Back to School: Empirical Evidence on Modeling in Software Development
 

Devnology Back to School: Empirical Evidence on Modeling in Software Development

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Modeling is a common part of modern day software engineering practice. Little scientific evidence is known about how models are made and how they help in producing better software. In this talk Michel ...

Modeling is a common part of modern day software engineering practice. Little scientific evidence is known about how models are made and how they help in producing better software. In this talk Michel Chaudron presents highlights from a decade of research that he has performed in the area of software modeling using UML. Topics that will be addressed: What is the state of UML modeling in practice? What are effective techniques for assessing the quality of UML models? How do engineers look at UML models? Do UML models actually help in creating better software?

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    Devnology Back to School: Empirical Evidence on Modeling in Software Development Devnology Back to School: Empirical Evidence on Modeling in Software Development Presentation Transcript

    • Zin en Onzin van Modeleren in Software Development Dr. Michel R.V. ChaudronLeiden Institute of Advanced Computer Science chaudron@liacs.nl Leiden University. The university to discover.
    • Outline of talk Introduction - LIACS & Software Engineering Modeling in Software Development - How are models being used in practice? - What does it cost/bring to do modeling? Experiments - Hafeez - Dave (announcement)Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Leiden Institute of Advanced Computer Science Algorithms Software Engineering Prof. J.N. Kok, Prof. T. Bäck Dr. M.R.V. Chaudron, Prof. F. Arbab, • Novel Algorithms • Data Mining • Software Design and Modeling 4 years Leiden • Natural Computing • Software Composition • Applications • Formal Methods 10 years TU Eindhoven • Drug Design • Coordination / Concurrency 2 year IT-company • Medicine • Engineering • Logistics • Physics Imagery and Media Core Computer Dr. M. Lew, Dr. F. Verbeek Technologies • Computer Vision and Audio/Video Prof. H. Wijshoff, Dr. T. Stefanov • Bioimaging • Multimedia Search • Embedded Systems • Internet Technology • Parallel / Distributed Computing • Computer Graphics • Compiler Technology3 Leiden University. The university to discover.
    • Software Engineering Researchers Werner Heijstek Hafeez Osman Dave Stikkolorum Ana Fernandes Pieter KwantesModels in Global SE Updating UML Teaching SW Design UML in maintenance Domain Specific Modeling Languages Ramin Etemadi Bilal Karasneh Peng Ye Javier Hernandez Optimizing Reasoning about Modeling Sw- Dr. Michel R.V. Chaudron Sw. Arch. Design Sw. Arch. Design Product Lines chaudron@liacs.nlDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Automated Updating of Class Models timesource code change  change ’ change ’’ learn design update with abstraction:  abstraction of change: () (’) (’’) UML design model A change  can be an addition, modification, removal. Leiden University. The university to discover.
    • Extracting Model from Images Bilal Recognizing: - Rectangles - Lines - Text, - arrow-headsInput: .jpeg, .png Output: XMI for the class model Leiden University. The university to discover.
    • History of UML Other modeling languages: BPML, Archimate, …Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • 4+1 Views Representation of System Architecture What can/does How is the system the system do ? How to build / structured? configure ? Logical View Development View System Architect End-user Programmers Functionality (Decomposition) Configuration management Use Case View How does the Where to install ? system behave? What hwnw is used? Process View Deployment View System Architect System engineering System topology Concurrency, Communication, Delivery, installation, maintenance Synchronization How does the Performance, Scalability, Throughput system perform ?Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • UML modeling notations for 4+1 Views Structure model : components, Config. Mngnt model packages, interfaces versioning policies A B file ownership Stakeholders & … Use cases view C D Behaviour model : Deployment model : MSC, state-diagrams physical model + mapping A B C D A C D B TCP/IP over Ethernet BC/WC e2e-response times, freq. bandwidth, availabilityDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Opinions on Value of ModellingValue Agile MDA “Loose UML” Formal Methods 100% Panel completeness Leiden University. The university to discover.
    • Introduction: Research Interest - What are the pay-offs of investing in early design/architecture/modeling? Fewer defects? Cheaper maintenance? … - Effectiveness of software modelling - Quality of Modeling When is a model good (enough) - Analysis of Non-Functional Quality Properties of architectures - Many modeling approaches around; focus on UML in custom software developmentDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Increasing Complexity of Software Blow, J. "Game Development: Harder Than You Think." ACM Queue 12Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Empirical Research … is a way of gaining knowledge by means of observation or experience. Theory Practice SE body of knowledge People/Skills, Processes, Methods, Technology, Artefacts Observation Hypothesis Prediction/Test Validation Topics: CMM, OO, Agile, MDA, … Methods: Experiment, Case study, Survey, Project Repositories …Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • contact Dr. Michel R.V. Chaudron Associate Professor Leiden Institute of Advanced Computer Science chaudron@liacs.nl www.liacs.nl/~chaudron If you have UML models you would like to assess? If you want advice on Quality Assurance for modeling? If you want to sponsor our research?Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Empirical Life-cycle Initial Idea Exploratory Interviews Survey Method Development Experiment Industrial Case Studies Leiden University. The university to discover.
    • Phase 1: Explore via Case Studies Your project here? Mail me: chaudron@liacs.nlDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Industrial use of UML diagrams How UML is used B Dobing, J Parsons - Communications of the ACM, 2006 ClassDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Styles of Modeling Sketch Communication Recipe for constructionDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Modelling style and model purpose Architecture and Design Description. IEEE Software 23(2): 40-46 (2006) C.F.J.Lange, M.R. V. Chaudron, J.Muskens: In Practice: UML Software understanding communicating managing complexity implementation blueprint Styles of using UML – as a sketch – thinking tool/understanding – for communicating system design – as a blueprint – guide the implementation work – as a implementation (MDA) - code generation Leiden University. The university to discover.
    • The Modeling SpectrumModel driven architecture: Principles and practice, Brown, A.W., Software and Systems Modeling, 2004 Leiden University. The university to discover.
    • Uses of Software Models + Understanding Doing + Analyzing / Predicting modeling is a quality + Communicating improving activity + GuidingDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • UML in practice Sketch Communication More effort  More expensive Recipe for constructionDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Modeling & Documentation in Agile Development - Agile principles: working software over comprehensive documentation Survey under 75+ agile developers Tending towards: we need a bit more Modeling is compatible with agile developmentChristoph J. Stettina and Werner Heijstek, Necessary and Neglected? An Empirical Study of Internal Documentation in Agile Software Development Teams 29th ACM Int. Conf. on Design of Communication , Pisa, ItalyDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Does use of UML improve software quality? Ariadi Nugroho, Michel R. V. Chaudron: A Survey of the Practice of Design - Code Correspondence amongst Professional Software Engineers. ESEM 2007: 50.0 45.0 Reduce Somewhat Reduce 45% Neutral 41% 40.0 Somewhat Improve Improve Percentage of the respondents 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 Cover Correctness Modularity Testability Understandability Requirements A large number of developers indicated the use of UML improves understandability and modularityDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Economic Model for Cost of Quality From: H. Krasner, Cost of Quality, 1998 Cost of SQ = Achievement Cost + Non-conformance CostDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Cost of Modeling Focus on effort “Is there a correlation between class-count and the effort spent in modeling?” Sources: ‐ Experiment ‐ Set of industrial case studiesDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Empirical Data  Experiment  106 MSc students in (TU/e)  Organized in 35 teams  Task: Model Car Navigation System  Duration: 6 weeks assignment  Three treatments were applied: 1. No modeling conventions 2. With modeling conventions 3. Tool-supported modeling conventionsDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Experiment Results: Effort ~ Size? 40,00 35,00 30,00 Effort (hours) 25,00 Spearman’s Correlation Coefficient 20,00 15,00 Effort (hours) 10,00 Class-count .302 5,00 Sig. (2-tailed) .171 0,00 0 10 20 30 40 50 60 70 Class-count Number of classes in design There is no significant correlation between class-count and the effort spent in modeling.  class-count is not a good measure for the effort spent on modeling?Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Measurement of Modeling/Design in RUP Effort Distribution modeling designingDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Impact of MDD on Effort Distribution as % of total project effort construction constr. elaboration transition transition elaboration architecture & code generator incep. ‘traditional’ Model-driven (avg. of 17 projects) (1 project) Leiden University. The university to discover.
    • Does Quality of Modeling Matter? An Industrial Case Study Focus on detail in a UML Model attributes operations associations Low detail High detailDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Relation between UML-LoD and Code Quality Select ‘defects’ in defect DB Find classes in source component C2 defect component C2 code that were requires I2 requires I3I2 requires uses requires I3 I2.g uses I2.g density uses I3.h repaired for solving this uses I3.h defects O rder OrderDetail * 1 -date P ce or repro ss Parser A er nalys DC B reator DF B iller Inherita R nce elator DC B hecker S tis Filte ta tic r StatisticC lculator a -quantity Find corresponding -status -taxS tatus SA A A T.B T +calcTax() +calcS ubTotal() +calcTotal() +calcW eight() +calcTotalW eight() Paym ent 1 -am ount 1 classes in UML models Credit -num ber -type -expDate Cash -cashTendered Check -nam e -bankID +authorized() + authorized() OrderDetail O rder LoD per class * 1 -date P ce repro ssor P rse a r A lys na er DC B reator DF B iller Inherita ceR n elator D C eck B h er S tisticFilte ta r StatisticC lc r a ulato -quantity Determine LoD -status -taxS tatus SA A A T.B T +calcTax() +calcS ubTotal() +calcTotal() +calcW eight() +calcTotalW eight() Paym ent 1 -am ount 1 for CD and SD -num ber -type -expDate Credit Cash -cashTendered Check -nam e -bankID +authorized() + authoriz ed()Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Relation between Level of Detail and Defect Density = 1 class Level of Detail for Sequence Diagrams is significantly (negatively) correlated with defect density. More detailed model => fewer defectsDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Quality Assurance for Software Design / UML Model - How to define Quality for design/model? - How to assess quality? - How to check conformance in code?Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Quality Models Existing models Boehm McCall ISO 9126 Rombach … - Decomposition of characteristics - Bottom level: metrics - Differences in - Relations between characteristics - Vocabulary Boehm’s Quality ModelDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • How to Define UML Model Quality? Framework for quality of UML models (Lange & Chaudron, 2005) The quality attributes of a UML model is determined by its purpose...Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • How to measure goodness of UML model? Design Heuristics - Coupling, Cohesion, absence of anti-patterns Completeness - Interaction of classes must be described in SD - Methods of CD must be called in SD Consistency - In many casesSD can not be automatically determineddiagram Messages in it must correspond to method in class whether a flaw is an incompleteness or an inconsistency Correspondence - Dependencies in the implementation are allowed only if they occur in the designDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Automatically Checking Quality of Design Quality = absence of ‘bad things’ such as omissions, spaghetti UML model UML Analysis Tool Quality Metrics/Rules • Completeness Visualization of • Consistency model + metricsDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Screenshot of the MetricView toolQuality Metrics• Completeness• Consistency• … extensible = violation = okDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • MetricView Tool MetaView to visualize the (hidden) inter-diagram relations Example: Which classes contribute to a certain use case? http://www.youtube.com/watch?v=G3HJ_QR9EG4 Supporting task-oriented modeling using interactive UML views, C.F.J. Lange, M. A.M. Wijns, and M. R.V. Chaudron, Journal of Visual Languages and ComputingDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover. Christian Lange 42
    • MetricView Tool MetricView The values of metrics arehttp://www.youtube.com/watch?v=G3HJ_QR9EG4 visualized on class diagrams using colors Example: Coupling-Between- Objects (CBO) We will analyse your UML model : mail to Chaudron@liacs.nl Supporting task-oriented modeling using interactive UML views, C.F.J. Lange, M. A.M. Wijns, and M. R.V. Chaudron, Journal of Visual Languages and Computing Christian Lange. Leiden University. The university to discover. 43
    • 3D visualization of design measurements Your cases welcome… http://www.youtube.com/watch?v=G3HJ_QR9EG4 Supporting task-oriented modeling using interactive UML views, C.F.J. Lange, M. A.M. Wijns, and M. R.V. Chaudron, Journal of Visual Languages and Computing Christian Lange. Leiden University. The university to discover. 44
    • Findings from State of the Practice UML is used in different ways for different purposes - Incompleteness - Modelers focus on complex and critical parts - Disproportion - Different parts of the system are modeled different in level of quality - Inconsistency - Conflicting information in different views of one model Quality Assurance for modeling should address theseDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Industrial Experience with MetricView as Quality Assurance Tool - Based on 15+ industrial projects - If there are weak spots in the design, then these are indicated as ‘suspects’ by MetricView - MetricView indicates many weak spots that do not require improvement according to project architects (false positives?)  prioritization is needed - The later MetricView is applied, the fewer ‘weak spots’ are removed from the design  process issueDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Understanding Effectiveness of Modeling through EyetrackingDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Hypothetical Benefits of Modeling UML Modeling Developer Process Product Benefits Benefits Benefits Better Improved Improved requirements Fewer Quality Understanding Defects Problem Domain Improved Design Reduced Improved Compliance rework Productivity Better Improved Reduced Understanding More efficient Design Quality testing Solution Space Testing effort Reduced More efficient Improved Shared maintenance Maintenance Communication System Model effort More Project Management Better Risk Accurate Benefits management EstimatingDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Concluding Remarks- Modeling is becoming common in software development. There are payoffs for modeling in: - improved code quality - improved communication- Empirical studies enhance alignment of research and practice – your input is needed- Practical Quality Assurance for UML should use low hanging fruit: i) Naming and layout-conventions, ii) Reviews & Inspections iii) Versioning, iv) MetricsDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Future Directions - Automated Reasoning about Designs - Diagnosis & Prioritization - Severity Assessment of design flaws / technical debt - Next: Empirical studies - by Hafeez & Arjan - by Dave Hafeez DaveDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Comparing “MDD with code generation” & “Modeling + Programming” MDD with code generation Modeling with ProgrammingRequires: Off the shelves tooling- stable domain- very good understanding of Standard language domain (staff hiring & turnover)- Multiple projects Divergence of model and code- Don’t introduce in critical projectsNeeds dedicated techniques for Quality Assurance, estimation Leiden University. The university to discover.
    • How often do design issues lead to problems? 70 Never Sometimes 60 Often Very Often Percentage of the respondents 50 40 30 20 10 0 Inconsistency Understandability Inaccuracy Incompleteness Incompleteness of models was considered most often to lead to implementation problemsDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • How do developers apply detail to UML models? Ariadi Nugroho, Michel R. V. Chaudron: A Survey of the Practice of Design - Code Correspondence amongst Professional Software Engineers. ESEM 2007: 70.0 Disagree Somewhat Disagree 61% 60.0 Neutral Somewhat agree 52% Percentage of the respondents 50.0 Agree 40.0 37% 30.0 20.0 10.0 0.0 Equal details Details proportional More details for Programmers for all parts to complexity critical parts determine details Developers apply more detail on critical and complex parts of a systemDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Which factor most often drives developers to Ariadi Nugroho, Michel R. V. Chaudron: A Survey of the Practice of Design - Code Correspondence amongst Professional Software Engineers. ESEM 2007: non-correspondence? Percentage of the respondents 60 Never 50 Sometimes Often Very Often 48% 40 30 31% 29% 20 10 0 Meeting Impractical Incomplete Model doesn’t satisfy deadline model model requirements Among other factors, developers considered incomplete model more often drives them to non-correspondenceDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Does strictness of implementing a model differ Ariadi Nugroho, Michel R. V. Chaudron: A Survey of the Practice of Design - Code Correspondence amongst Professional Software Engineers. ESEM 2007: for different modeling constructs? 50.0 Loosely 36% Percentage of the respondents Somewhat loosely 45.0 Neutral 40.0 Somewhat strict Strictly 46% 35.0 30.0 31% 25.0 20.0 15.0 10.0 5.0 0.0 Package Dependency Inheritance Class and The order of structure relations relations method names method calls Developers favor to implement dependency and inheritance relations more strictly than other constructsDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Which classes are modeled? Complexity and Coupling is higher for classes that are modeled than not modeledDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Maintenance paradox - Maintainers of software would like better documentation - Even if UML models are created during design Too detailed models become outdated Better abstraction in reverse- / round trip- engineering is needed in the setting of incremental & iterative developmentDr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Practical QA for UML modeling Naming and layout-conventions The Elements of UML2.0 Style, Scott Ambler, Cambridge Univ Press, 2005 Low Hanging Fruit (c) Erin Witzel, 2010 Reviews & Inspections Guidelines by e.g. Shull et.al., Biffl, Version Management Many tools around (e.g. CVS, SVN, …) Metrics SDMetrics http://www.sdmetrics.com/Dr. Michel R.V. Chaudron, Devnology, June 2012, Leiden Leiden University. The university to discover.
    • Investigations into effectiveness of software modelingMetricView contributors Johan Muskens Christian Lange Martijn Wijns Dennis van Opzeeland Ariadi Nugroho Werner Heijstek Maurice Vermeer Alex Telea Robin van den Broek MRV Chaudron Sheet 59
    • Publications Investigations into effectiveness of software modeling Journal Publications  Supporting task-oriented modeling using interactive UML views. PDF C.F.J. Lange, M.A.M. Wijns, M.R.V. Chaudron. Journal of Visual Languages and Computing (Elsevier), Volume 18, Issue 7, August 2007.  In Practice: UML Software Architecture and Design Description. C.F.J. Lange, M.R.V. Chaudron, J. Muskens. IEEE Software, Volume 23, Issue 2, March 2006. Conference Publications  A Visualization Framework for Task-Oriented Modeling using UML. C.F.J. Lange, M.A.M. Wijns, M.R.V. Chaudron. Proceedings of the 40th Annual Hawaii International Conference on System Sciences (HICSS07). January 2007.  An Experimental Investigation of UML Modeling Conventions. C.F.J. Lange, Bart DuBois, M.R.V. Chaudron, Serge Demeyer. Proceedings of the ACM/IEEE International Conference on Model- driven Engineering Languages and Systems (MoDELS 2006). October 2006.  Effects of Defects in UML Models - An Experimental Investigation. C.F.J. Lange, M.R.V. Chaudron. Proceedings of the International Conference on Software Engineering (ICSE 2006). May 2006. (acceptance rate: 9%)  Improving the Quality of UML Models in Practice. C.F.J. Lange. Proceedings of the International Conference on Software Engineering (ICSE 2006). May 2006.  Visual Exploration of Combined Architectural and Metric Information. M. Termeer, C.F.J. Lange, A. Telea, M.R.V. Chaudron. Proceedings of VISSOFT 2005, IEEE CS Press. September 2005.  Combining Metrics Data and the Structure of UML Models using GIS Visualisation Approaches. C.F.J. Lange, M.R.V. Chaudron. IEEE International Conference on Information Technology 2005. Las Vegas, April 2005.  An Exploratory Study on the Industrial Use of UML: Improving Control over Design Quality. C.F.J. Lange, M.R.V. Chaudron. JACQUARD Conference. February 2005.  Investigations in Applying Metrics to Multi-View Architecture Models. J. Muskens, M.R.V. Chaudron, C.F.J. Lange. In Proceedings of EUROMICRO’04, Rennes, France, September 2004.  An Empirical Assessment of Completeness in UML Design. C.F.J. Lange, M.R.V. Chaudron. Proceedings of the 8th Conference on Empirical Assessment in Software Engineering (EASE04). May 2004.  Konsistenz und Vollständigkeit industrieller UML Modelle. C.F.J. Lange, M.R.V. Chaudron. Proceedings of “Modellierung 2004“, Marburg, Germany, 24-26 March 2004. Workshop Publications  Towards Task-Oriented Modeling using UML. C.F.J. Lange, M.A.M. Wijns, M.R.V. Chaudron. Proceedings of the 10th QAOOSE workshop, co-located with ECOOP2006. July 2006.  Managing Model Quality in UML-based Software development. C.F.J. Lange, M.R.V. Chaudron. Proceedings of IEEE Conference on Software Technology and Engineering Practice 2005 (STEP), in the "Workshop on Software Process Improvement, Quality Assurance and Measurement. September 2005.  Michel Chaudron, Christian Lange, Martijn for the Assessment of Correspondence between UML Designs and Implementations. Quantitative Techniques Wijns 60 Dennis J.A. van Opzeeland, Christian F.J. Lange, Michel R.V. Chaudron. Proceedings of the 9th QAOOSE workshop, co-located with ECOOP2005. July 2005.