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

Maria Grazia Pia, INFN Genova 1

Part II

Software engineering Geant4

rigorous approach to software


Part II: outline

Motivations for software engineering in HEP

The software process

Components of the software life-cycle

Object Oriented technologies

Brief digression on basic OO concepts

OOAD in Geant4

Quality Assurance

Standards


Why software engineering in HEP?

Software engineering is somewhat new to the HEP environment other engineering branches more consolidated in

this environment (mechanics, electronics, accelerators etc.)

Benefits derive from a rigorous approach to software the lesson can be learned from the world of

software professionals! even the most talented professionals need an

organized environment to do cooperative work 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.


Software engineering strategies in Geant4

Software engineering plays a fundamental role in Geant4

The software process Requirements Analysis and Design Object Oriented methodologies Quality Assurance Testing Physics validation


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: the Waterfall model the Iterative Incremental Development model

The Waterfall model analysis design coding each phase starts following the completion of

the previous one The Iterative Incremental Development model

cycles of analysis design coding, with incremental refinement


The software process in Geant4

Based on the Booch methodology choice resulting from a thorough study of

various models critically evaluated and adapted to the Geant4

peculiar environment

Spiral-type software process: cycles of incremental

analysis design implementation testing iterations


Requirements

Requirements are the quantifiable and verifiable behaviours that a system must possess constraints that a system must work within

User requirements this phase defines the scope of the system

Software requirements this is the analysis phase of a software project 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! ability to cope with the evolution of the

requirements


Geant4 requirements

Geant4 has adopted a rigorous approach to requirements user requirements collected from the user

communities in the initial phase

coded according the PSS-05 standard

Geant4 User Requirements Document continuously updated


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 abstraction encapsulation modularity hierarchy typing concurrency persistence

brought together in a synergistic way

Geant4 is based on Object Oriented technology


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”.


Some fundamental concepts in OOD -1

The Open Closed Principle Open for extension, Closed for modification

A software module that is designed to be reusable, maintainable and robust must be extensible without requiring modification

new features are added by adding new code, rather than by changing old, already working, code

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

Derived types must be substitutable for their base types

It is an important feature for conforming to the OCP


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

Both high level policy and low level details should depend on abstractions

This ensures reusability and maintainability 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 Polluted interfaces generate unnecessary couplings We want to separate interfaces whenever possible to

avoid the disadvantages of couplings


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


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 they are best done concurrently

The output of OOAD is a set of class and object diagrams, showing the static structure the collaborations


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: a Meta-model a notation

UML has a standard data representation, that is called the Meta-model

the Meta-Model is a description of UML in UML 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:

a notation for modeling the static elements of a design (classes, attributes, relationships...)

a notation for modeling the dynamic elements of a design (objects, messages, finite state machines...)


An example of a class diagram


Another example of a class diagram


C++

OO technology and C++ are not equivalent! OO methodologies can be implemented in a variety

of languages, not only in C++ 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:

I. Pohl, OO programming using C++ S. B. Lippman, J. Lajoie, C++ primer B. Stroustrup, The C++ programming language G. Booch, OO analysis and design R. Martin, Designing OO C++ applications using the

Booch method


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


Benefits from OO technology

The OO technology provides various benefits to Geant4

Transparency decoupling from implementation

Flexibility alternative models and implementations

Openness to evolution extensibility, implementation of new models and

algorithms without interfering with existing software

possibility for the user to extend the toolkit with his/her model and data

Interface to external software, without dependencies databases for persistency visualisation libraries tools for UI etc.


Geant4 class category diagram


Quality Assurance

Extensive use of Quality Assurance systems fundamental for a toolkit of wide public use

Commercial tools Insure++, Logiscope etc.

C++ coding guidelines scripts to verify their applications automatically

Code inspections within working groups and across groups

Testing Unit testing in most cases down to class level granularity Integration testing sets of logically connected classes Test-bench for each category eg.: test-suite of 375 tests for hadronic physics

parameterised models System testing exercising all Geant4 functionalities in realistic set-ups Physics testing comparisons with experimental data Performance Benchmarks


Standards

Geant4 is based on standards (ISO and de facto)

STEP engineering and CAD systems

ODMG RD45

OpenGL e VRML for graphics

CVS for code management

C++ as programming language

UML as modeling language


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)?

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

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