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Object-Oriented Design in Practice. Could/Should We Do Better?

Object-Oriented Design in Practice. Could/Should We Do Better?. Dr. Radu Marinescu. Problems with (Object-Oriented) Design. From Dreams to Reality Dreams : object-oriented mechanisms will automatically increase the quality of software e.g. make systems easier to maintain or reuse

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Object-Oriented Design in Practice. Could/Should We Do Better?

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  1. Object-Oriented Design in Practice.Could/Should We Do Better? Dr. Radu Marinescu

  2. Problems with (Object-Oriented) Design • From Dreams to Reality • Dreams: object-oriented mechanisms will automatically increase the quality of software • e.g. make systems easier to maintain or reuse • Reality: uncountable number of OO legacy systems in the industry • inflexible, hard to understand, hard to extend… • Why? • Time Pressure • Changing Requirements • Immature Developers

  3. Design and Quality • …“Design is hard”[Opdyke92] • Object-oriented design makes no exception... • Quality is in danger Software needs designbut… Pressure of the market to control of qualitybut… • …“You can’t control what you can’t measure”[DeMarco82] • What should we measure? • How should we measure?

  4. Design Flaws… Why care? • Design problems are frequent • legacy systems with high business value • must maintain and enhancethe system • Design problems are expensive • high effort required for maintenance and extension • Design problems will always be there! • at least because of time pressure. • …but I believe also because of changing requirements ... are malign characteristics of design entities • hinder the maintenance and evolution of the system • by violating the principles and rules of good (OO) design

  5. ...33% of all the classes in the system may require changes?! Just Imagine that... ...you would change just a small design fragment and suddenly...

  6. Is There Any Hope? • “There is no silver bullet!”[Brooks84] • Encapsulation? Inheritance? Polymorphism? • NO! These are just mechanisms • Like in chess... • … just knowing the pieces and the moves is not enough • But there is hope! • Design rules, guidelines and heuristics • Apply them and they will provide the desired quality • Break them and they will break your design! How could we control the usage of design rules ? Hard to control, because rules are hard to quantify!

  7. Problem Detection • The process of identifying the parts of a software system affected by a particular design flaw • It‘s not easy! • manual and empirical • time-expensive and non-scalable • "Measuring" the Design • map source-code entities to numerical values • used as quality indicators Detection of Design Problems Idea:Use metrics to detect design problems!

  8. Problems with Software Measurement • Definitions of Metrics • Mapping attributes of a software product to numeric values [Fent97] • Imprecise, confusing, or conflicting definitions • Interpretation Models • Not provided or hardly reusable in a different context • Interpretation level is too fine-grained to lead to design decisions • metrics values are like symptoms • indicate an abnormality, but can’t indicate the cause • reduces the relevance of measurement results There is a large gap between what we do measure and what we should measure! Need mechanism for higher-level interpretation of metrics!

  9. Detection Strategy • Generic mean for defining metrics-based design rules • use metrics together! • Based on mechanisms of filtering and composition • Filtering Mechanism • Statistical functions that return a subset of a data-set • Composition Operators • articulate the composition of a detection rule Themeasurable expression of a rule, by which design fragments that are conformant to the rule can be identified in the source-code

  10. Analysis Select Metrics Detection Strategy Defining a Detection Strategy Detection Technique Informal Rules (design-related) • access many “foreign” data • large and complex classes • or non-cohesive • Top-level classes in a design should • share work uniformly • Beware of classes with much • non-communicative behavior • Beware of classes that access directly • data from other classes AOFD TopValues(20%)and... WMCHigherThan(30) or TCCLowerThan(0.33)

  11. Classification of Design Flaws

  12. ProDeOOS at Work ...

  13. Sources (Java, C++) parsing Meta-Model using Metrics 1 .. n Detection Strategy (*.sod) executing with PRODEOOS List of Candidates 1 .. m Statistical Filters manual inspection Process of Design Inspection

  14. Summary • Design flaws are dangerous • the larger the system, the higher the risk • We can assess the quality of design • by measuring its conformance to principles of OO design • Ability to detect a significant set of design flaws • at all levels, from methods to subsystems • Strong tool support for the entire approach • high degree of automatization and scalability

  15. Could We Do Better ... for You? • Approach successfully applied on industrial systems • > 100.000 LOC and up to 5.000.000 LOC • proved to be scalable and accurate • Concepts already implemented in two important CASE tools • metrics (since 2001) and detection strategies (since 2002) • in Borland Together CC and WSE • second important CASE tool provider interested in implementing the concepts. • Consultancy for software companies on quality assurance and re-engineering • all over Europe, for the last 3.5 years ! This is not just about science and research!

  16. Should We Do Better... Together?

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