| 1 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 3. Toolkit Fundamentals</title><link rel="stylesheet" href="../xml/XSLCustomizationLayer/G4HTMLStylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.1"><link rel="start" href="index.html" title="Geant4 User's Guide for Application Developers"><link rel="up" href="index.html" title="Geant4 User's Guide for Application Developers"><link rel="prev" href="ch02s10.html" title="2.10. How to Visualize the Detector and Events"><link rel="next" href="ch03s02.html" title="3.2. Global Usage Classes"><script language="JavaScript">
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| 8 | </script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3.
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| 9 | Toolkit Fundamentals
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| 10 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s10.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch03s02.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="chap.ToolkitFundamentals"></a>Chapter 3.
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| 11 | Toolkit Fundamentals
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| 12 | </h2></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sect.ClassCate"></a>3.1.
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| 13 | Class Categories and Domains
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| 14 | </h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.ClassCate.WhatIsClassCate"></a>3.1.1.
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| 15 | What is a class category?
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| 16 | </h3></div></div></div><p>
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| 17 | In the design of a large software system such as Geant4, it is
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| 18 | essential to partition it into smaller logical units. This makes
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| 19 | the design well organized and easier to develop. Once the logical
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| 20 | units are defined independent to each other as much as possible,
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| 21 | they can be developed in parallel without serious interference.
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| 22 | </p><p>
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| 23 | In object-oriented analysis and design methodology by Grady Booch
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| 24 | [<span class="citation">
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| 25 | <a href="bi01.html#biblio.booch1994">
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| 26 | Booch1994
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| 27 | </a>
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| 28 | </span>]
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| 29 | , class categories are used to
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| 30 | create logical units. They are defined as "clusters of classes that
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| 31 | are themselves cohesive, but are loosely coupled relative to other
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| 32 | clusters." This means that a class category contains classes which
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| 33 | have a close relationship (for example, the "has-a" relation).
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| 34 | However, relationships between classes which belong to different
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| 35 | class categories are weak, i.e., only limitted classes of these
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| 36 | have "uses" relations. The class categories and their relations are
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| 37 | presented by a class category diagram. The class category diagram
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| 38 | designed for Geant4 is shown in the figure below. Each box in the
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| 39 | figure represents a class category, and a "uses" relation by a
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| 40 | straight line. The circle at an end of a straight line means the
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| 41 | class category which has this circle uses the other category.
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| 42 |
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| 43 | </p><div class="figure"><a name="fig.G4ClassCategory"></a><div class="figure-contents"><div class="mediaobject" align="center"><img src="./AllResources/Fundamentals/classCategory.gif" align="middle" alt="Geant4 class categories"></div></div><p class="title"><b>Figure 3.1.
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| 44 | Geant4 class categories
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| 45 | </b></p></div><p><br class="figure-break">
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| 46 | </p><p>
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| 47 | The file organization of the Geant4 codes follows basically the
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| 48 | structure of this class cateogory. This <span class="emphasis"><em>User's Manual</em></span>
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| 49 | is also organized according to class categories.
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| 50 | </p><p>
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| 51 | In the development and maintenance of Geant4, one software team
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| 52 | will be assigned to a class category. This team will have a
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| 53 | responsibility to develop and maintain all classes belonging to the
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| 54 | class category.
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| 55 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.ClassCate.ClassCateInGeant4"></a>3.1.2.
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| 56 | Class categories in Geant4
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| 57 | </h3></div></div></div><p>
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| 58 | The following is a brief summary of the role of each class category
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| 59 | in Geant4.
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| 60 |
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| 61 | </p><div class="orderedlist"><ol type="1" compact><li><p><span class="bold"><strong>Run and Event</strong></span>
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| 62 | </p><p>These are categories related to the generation of events,
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| 63 | interfaces to event generators, and any secondary particles
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| 64 | produced. Their roles are principally to provide particles to be
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| 65 | tracked to the Tracking Management.
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| 66 | </p><p>
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| 67 | </p></li><li><p><span class="bold"><strong>Tracking and Track</strong></span>
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| 68 | </p><p>These are categories related to propagating a particle by
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| 69 | analyzing the factors limiting the step and applying the relevant
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| 70 | physics processes. The important aspect of the design was that a
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| 71 | generalized Geant4 physics process (or interaction) could perform
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| 72 | actions, along a tracking step, either localized in space, or in
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| 73 | time, or distributed in space and time (and all the possible
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| 74 | combinations that could be built from these cases).
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| 75 | </p><p>
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| 76 | </p></li><li><p><span class="bold"><strong>Geometry and Magnetic Field</strong></span>
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| 77 | </p><p>These categories manage the geometrical definition of a detector
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| 78 | (solid modeling) and the computation of distances to solids (also
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| 79 | in a magnetic field). The Geant4 geometry solid modeler is based on
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| 80 | the ISO STEP standard and it is fully compliant with it, in order
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| 81 | to allow in future the exchange of geometrical information with CAD
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| 82 | systems. A key feature of the Geant4 geometry is that the volume
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| 83 | definitions are independent of the solid representation. By this
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| 84 | abstract interface for the G4 solids, the tracking component works
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| 85 | identically for various representations. The treatment of the
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| 86 | propagation in the presence of fields has been provided within
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| 87 | specified accuracy. An OO design allows us to exchange different
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| 88 | numerical algorithms and/or different fields (not only B-field),
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| 89 | without affecting any other component of the toolkit.
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| 90 | </p><p>
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| 91 | </p></li><li><p><span class="bold"><strong>Particle Definition and Matter</strong></span>
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| 92 | </p><p>These two categories manage the the definition of materials and
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| 93 | particles.
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| 94 | </p><p>
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| 95 | </p></li><li><p><span class="bold"><strong>Physics</strong></span>
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| 96 | </p><p>This category manages all physics processes participating in the
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| 97 | interactions of particles in matter. The abstract interface of
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| 98 | physics processes allows multiple implementations of physics models
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| 99 | per interaction or per channel. Models can be selected by energy
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| 100 | range, particle type, material, etc. Data encapsulation and
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| 101 | polymorphism make it possible to give transparent access to the
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| 102 | cross sections (independently of the choice of reading from an
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| 103 | ascii file, or of interpolating from a tabulated set, or of
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| 104 | computing analytically from a formula). Electromagnetic and
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| 105 | hadronic physics were handled in a uniform way in such a design,
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| 106 | opening up the physics to the users.
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| 107 | </p><p>
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| 108 | </p></li><li><p><span class="bold"><strong>Hits and Digitization</strong></span>
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| 109 | </p><p>These two categories manage the creation of hits and their use
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| 110 | for the digitization phase. The basic design and implementation of
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| 111 | the Hits and Digi had been realized, and also several prototypes,
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| 112 | test cases and scenarios had been developed before the
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| 113 | alpha-release. Volumes (not necessarily the ones used by the
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| 114 | tracking) are aggregated in sensitive detectors, while hits
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| 115 | collections represent the logical read out of the detector.
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| 116 | Different ways of creating and managing hits collections had been
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| 117 | delivered and tested, notably for both single hits and calorimetry
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| 118 | hits types. In all cases, hits collections had been successfully
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| 119 | stored into and retrieved from an Object Data Base Management
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| 120 | System.
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| 121 | </p><p>
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| 122 | </p></li><li><p><span class="bold"><strong>Visualization</strong></span>
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| 123 | </p><p>This manages the visualization of solids, trajectories and hits,
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| 124 | and interacts with underlying graphical libraries (the
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| 125 | Visualization class category). The basic and most frequently used
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| 126 | graphics functionality had been implemented already by the
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| 127 | alpha-release. The OO design of the visualization component allowed
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| 128 | us to develop several drivers independently, such as for OpenGL, Qt and
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| 129 | OpenInventor (for X11 and Windows), DAWN, Postscript (via DAWN) and
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| 130 | VRML.
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| 131 | </p><p>
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| 132 | </p></li><li><p><span class="bold"><strong>Interfaces</strong></span>
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| 133 | </p><p>This category handles the production of the graphical user
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| 134 | interface (GUI) and the interactions with external software
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| 135 | (OODBMS, reconstruction etc.).
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| 136 | </p><p>
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| 137 | </p></li></ol></div><p>
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| 138 | </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02s10.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch03s02.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">2.10.
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| 139 | How to Visualize the Detector and Events
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| 140 | </td><td width="20%" align="center"><a accesskey="h" href="index.html"><img src="AllResources/IconsGIF/home.gif" alt="Home"></a></td><td width="40%" align="right" valign="top"> 3.2.
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| 141 | Global Usage Classes
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| 142 | </td></tr></table></div></body></html>
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