1. Maria Grazia Pia, INFN Genova 1 Part II Software engineering Geant4 rigorous approach to software

2. Maria Grazia Pia, INFN Genova 2 Part II: outline 3Motivations for software engineering in HEP 3The software process 3Components of the software life-cycle 3Object Oriented technologies 3Brief digression on basic OO concepts 3OOAD in Geant4 3Quality Assurance 3Standards

3. Maria Grazia Pia, INFN Genova 3 Why software engineering in HEP? ]Software engineering is somewhat new to the HEP environment l other engineering branches more consolidated in this environment (mechanics, electronics, accelerators etc.) ]Benefits derive from a rigorous approach to software l the lesson can be learned from the world of software professionals! l even the most talented professionals need an organized environment to do cooperative work l advanced technology cannot be fully effective without an organizational framework The question I am always asked at this point: Is there any room for creativity? Yes! Also in other disciplines a rigorous approach can be combined with creativity: architecture, music etc.

4. Maria Grazia Pia, INFN Genova 4 Software engineering strategies in Geant4 Software engineering plays a fundamental role in Geant4 v The software process v Requirements v Analysis and Design v Object Oriented methodologies v Quality Assurance v Testing v Physics validation

5. Maria Grazia Pia, INFN Genova 5 The software process It is the set of actions, tasks and procedures involved in producing a software system, through its life-cycle ]Complex domain, evolving, with many types of models available; some examples of software process models are, for instance: l the Waterfall model l the Iterative Incremental Development model ]The Waterfall model analysis  design  coding l each phase starts following the completion of the previous one ]The Iterative Incremental Development model cycles of analysis  design  coding, with incremental refinement

6. Maria Grazia Pia, INFN Genova 6 The software process in Geant4 ]Based on the Booch methodology l choice resulting from a thorough study of various models l critically evaluated and adapted to the Geant4 peculiar environment ]Spiral-type software process: cycles of incremental analysis  design  implementation  testing iterations

7. Maria Grazia Pia, INFN Genova 7 Requirements ]Requirements are the quantifiable and verifiable l behaviours that a system must possess l constraints that a system must work within ]User requirements l this phase defines the scope of the system ]Software requirements l this is the analysis phase of a software project l builds a model describing what the software has to do (not how to do it) ]Requirements are subject to evolution in the lifetime of a software project! èability to cope with the evolution of the requirements

8. Maria Grazia Pia, INFN Genova 8 Geant4 requirements Geant4 has adopted a rigorous approach to requirements l user requirements collected from the user communities in the initial phase l coded according the PSS-05 standard èGeant4 User Requirements Document l continuously updated

9. Maria Grazia Pia, INFN Genova 9 Object Oriented technology ]OO technology is built upon a sound engineering foundation, whose elements are called the object model ]The object model encompasses the principles of l abstraction l encapsulation l modularity l hierarchy l typing l concurrency l persistence brought together in a synergistic way Geant4 is based on Object Oriented technology

10. Maria Grazia Pia, INFN Genova 10 What is an object? G. Booch (in OOAD with Applications): “An object has state, behaviour and identity; the structure and behaviour of similar objects are defined in their common class”.

11. Maria Grazia Pia, INFN Genova 11 Some fundamental concepts in OOD -1 ]The Open Closed Principle Open for extension, Closed for modification l A software module that is designed to be reusable, maintainable and robust must be extensible without requiring modification l new features are added by adding new code, rather than by changing old, already working, code l The primary mechanisms behind are abstraction and polymorphism ]The Liskov Substitution Principle Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it l Derived types must be substitutable for their base types l It is an important feature for conforming to the OCP

12. Maria Grazia Pia, INFN Genova 12 Some fundamental concepts in OOD -2 ]The Dependency Inversion Principle Modules that implement high level policy should not depend on the modules that implement low level details l Both high level policy and low level details should depend on abstractions l This ensures reusability and maintainability l The interdependence makes a design rigid, fragile and immobile: a single change triggers a cascade of changes in dependent modules ]The Interface Segregation Principle Clients should not be forced to depend on interfaces that they do not use l Polluted interfaces generate unnecessary couplings l We want to separate interfaces whenever possible to avoid the disadvantages of couplings

13. Maria Grazia Pia, INFN Genova 13 Analysis Webster definitions: ]separation or breaking up of a whole into its fundamental elements or component parts ]a detailed examination of anything complex ]the practice of proving a mathematical proposition by assuming the result and reasoning back to the data or already established principles In the software world: ]it is the decomposition of a problem into its constituent parts ]it is accomplished by beginning with a set of stated requirements, and reasoning back from those requirements to a set of established software components and structures ]OOA is the act of determining the abstractions that underlie the requirements ]In OOA the components are objects and their collaborations

14. Maria Grazia Pia, INFN Genova 14 Design ]Design embodies the set of decisions that determine how the components will look like ]In OOD typically class inheritance and composition hierarchies are among the decisions ]OOA and OOD cooperate synergically l they are best done concurrently ]The output of OOAD is a set of class and object diagrams, showing l the static structure l the collaborations

15. Maria Grazia Pia, INFN Genova 15 UML: Unified Modeling Language ]UML has the goal to become a common language for creating models of OO software ]UML represents a unification of the concepts and notations previously in use (Booch, OMT) ]UML is comprised of two major components: l a Meta-model l a notation ]UML has a standard data representation, that is called the Meta-model l the Meta-Model is a description of UML in UML l it describes the objects, attributes and relationships necessary to represents the concepts of UML within a software application ]UML notation is comprised of two major subdivisions: l a notation for modeling the static elements of a design (classes, attributes, relationships...) l a notation for modeling the dynamic elements of a design (objects, messages, finite state machines...)

16. Maria Grazia Pia, INFN Genova 16 An example of a class diagram

17. Maria Grazia Pia, INFN Genova 17 Another example of a class diagram

18. Maria Grazia Pia, INFN Genova 18 C++ ]OO technology and C++ are not equivalent! l OO methodologies can be implemented in a variety of languages, not only in C++ l One can write procedural code in C++, that is not object oriented ]C++ provides many features that make it suitable for OO implementations of large scale software projects ]An overview of C++ language features and OO technology is beyond the scope of these lectures ]Many textbooks, courses and online material are available as learning aids; a few references: l I. Pohl, OO programming using C++ l S. B. Lippman, J. Lajoie, C++ primer l B. Stroustrup, The C++ programming language l G. Booch, OO analysis and design l R. Martin, Designing OO C++ applications using the Booch method

19. Maria Grazia Pia, INFN Genova 19 OOAD in Geant4 [Geant4 fully exploits the power of OOAD [The basic principles of OOD described in the previous transparencies are applied in Geant4 [They ensure a software that is reusable, maintainable, robust, extensible [OOAD is fundamental in Geant4 for a distributed parallel approach every part can be developed, refined, maintained independently [Problem domain decomposition and OOAD result in a unidirectional dependency of class categories [Booch/UML notations [CASE Tool: Rational Rose

20. Maria Grazia Pia, INFN Genova 20 Benefits from OO technology The OO technology provides various benefits to Geant4 ]Transparency l decoupling from implementation ]Flexibility l alternative models and implementations ]Openness to evolution l extensibility, implementation of new models and algorithms without interfering with existing software l possibility for the user to extend the toolkit with his/her model and data ]Interface to external software, without dependencies l databases for persistency l visualisation libraries l tools for UI l etc.

21. Maria Grazia Pia, INFN Genova 21 Geant4 class category diagram

22. Maria Grazia Pia, INFN Genova 22 Quality Assurance ]Extensive use of Quality Assurance systems l fundamental for a toolkit of wide public use ]Commercial tools l Insure++, Logiscope etc. ]C++ coding guidelines l scripts to verify their applications automatically ]Code inspections l within working groups and across groups ]Testing l Unit testing in most cases down to class level granularity l Integration testing sets of logically connected classes l Test-bench for each category eg.: test-suite of 375 tests for hadronic physics parameterised models l System testing exercising all Geant4 functionalities in realistic set-ups l Physics testing comparisons with experimental data l Performance Benchmarks

23. Maria Grazia Pia, INFN Genova 23 Standards Geant4 is based on standards (ISO and de facto) ]STEP l engineering and CAD systems ]ODMG l RD45 ]OpenGL e VRML l for graphics ]CVS l for code management ]C++ l as programming language ]UML l as modeling language

24. Maria Grazia Pia, INFN Genova 24 System of Units ]Geant4 is independent from any system of units ]All numerical quantities are expressed with their units explicitly ]The user is not constrained to using any specific system of units in his/her application Have you heard of the “incident” with NASA’s Mars Climate Orbiter ($125 million)?