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| 12 | <BODY>
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| 13 | <BR>
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| 14 |
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| 15 | <TABLE WIDTH="100%" >
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| 16 | <TR>
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| 17 | <TD>
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| 18 |
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| 19 | </A>
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| 20 | <A HREF="index.html">
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| 21 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents" HEIGHT=16 WIDTH=59></A>
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| 22 | <A>
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| 23 | <IMG SRC="../../../../resources/html/IconsGIF/PreviousGR.gif" ALT="Previous" HEIGHT=16 WIDTH=59></A>
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| 26 | </TD>
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| 27 |
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| 28 | <TD ALIGN=RIGHT>
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| 29 | <FONT COLOR="#238E23"><FONT SIZE=-1>
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| 30 | <B>Geant4 User's Guide</B></FONT></FONT>
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| 31 | <BR><FONT COLOR="#238E23"><FONT SIZE=-1>
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| 32 | <B>For Application Developers</B> </FONT></FONT>
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| 33 | <BR><FONT COLOR="#238E23"><FONT SIZE=-1>
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| 34 | <B>Toolkit Fundamentals</B> </FONT></FONT></TD>
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| 35 | </TR>
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| 36 | </TABLE>
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| 37 | <P><BR>
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| 38 |
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| 39 | <CENTER>
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| 40 | <FONT COLOR="#238E23"><FONT SIZE=+3>
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| 41 | <B>3.1 Class Categories and Domains</B></FONT></FONT>
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| 42 | </CENTER>
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| 43 | <P><BR>
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| 44 |
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| 45 | <HR ALIGN="Center" SIZE="7%">
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| 46 |
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| 47 | <P>
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| 48 | <a name="3.1.1">
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| 49 | <H2>3.1.1 What is a class category?</H2></a>
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| 50 |
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| 51 | In the design of a large software system such as Geant4, it is essential to
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| 52 | partition it into smaller logical units. This makes the design well organized
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| 53 | and easier to develop. Once the logical units are defined independent to
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| 54 | each other as much as possible, they can be developed in parallel without
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| 55 | serious interference.
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| 56 | <P>
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| 57 | In object-oriented analysis and design methodology by Grady Booch <a href="#GBooch">[1]</a>,
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| 58 | class categories are used to create logical units. They are defined as
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| 59 | "clusters of classes that are themselves cohesive, but are loosely coupled
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| 60 | relative to other clusters." This means that a class category contains
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| 61 | classes which have a close relationship (for example, the "has-a" relation).
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| 62 | However, relationships between classes which belong to different class
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| 63 | categories are weak, i.e., only limitted classes of these have "uses"
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| 64 | relations. The class categories and their relations are presented by
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| 65 | a class category diagram. The class category diagram designed for
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| 66 | Geant4 is shown in the figure below. Each box in the figure represents
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| 67 | a class category, and a "uses" relation by a straight line. The circle
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| 68 | at an end of a straight line means the class category which has this
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| 69 | circle uses the other category.
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| 70 | <P>
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| 71 | <center>
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| 72 | <IMG SRC="../../../../Welcome/IntroductionToGeant4/html/introductionToGeant4.src/classCategory.gif">
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| 73 | </center>
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| 74 | <P>
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| 75 | The file organization of the Geant4 codes follows basically the structure
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| 76 | of this class cateogory. This <i>User's Manual</i> is also organized according
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| 77 | to class categories.
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| 78 | <P>
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| 79 | In the development and maintenance of Geant4, one software team will
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| 80 | be assigned to a class category. This team will have a responsibility to
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| 81 | develop and maintain all classes belonging to the class category.
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| 82 | <BR>
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| 83 | <P>
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| 84 |
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| 85 | <HR>
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| 86 | <a name="3.1.2">
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| 87 | <H2>3.1.2 Class categories in Geant4</H2></a>
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| 88 |
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| 89 | The following is a brief summary of the role of each class category in Geant4.
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| 90 | <P>
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| 91 | <ol>
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| 92 | <li><b>Run and Event</b>
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| 93 | <p>
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| 94 | These are categories related to the generation of events, interfaces
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| 95 | to event generators, and any secondary particles produced. Their roles
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| 96 | are principally to provide particles to be tracked to the Tracking Management.
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| 97 | <p>
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| 98 | <li><b>Tracking and Track</b>
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| 99 | <p>
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| 100 | These are categories related to propagating a particle by analyzing the factors
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| 101 | limiting the step and applying the relevant physics processes. The important
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| 102 | aspect of the design was that a generalized Geant4 physics process (or
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| 103 | interaction) could perform actions, along a tracking step, either localized
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| 104 | in space, or in time, or distributed in space and time (and all the possible
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| 105 | combinations that could be built from these cases).
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| 106 | <p>
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| 107 | <li><b>Geometry and Magnetic Field</b>
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| 108 | <p>
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| 109 | These categories manage the geometrical definition of a detector
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| 110 | (solid modeling) and the computation of distances to solids
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| 111 | (also in a magnetic field). The Geant4 geometry
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| 112 | solid modeler is based on the ISO STEP standard and it is fully compliant
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| 113 | with it, in order to allow in future the exchange of geometrical information with CAD
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| 114 | systems. A key feature of the Geant4 geometry is that the volume definitions
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| 115 | are independent of the solid representation. By this abstract interface
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| 116 | for the G4 solids, the tracking component works identically for various
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| 117 | representations. The treatment of the propagation in the presence of fields
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| 118 | has been provided within specified accuracy. An OO design allows us to
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| 119 | exchange different numerical algorithms and/or different fields (not only
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| 120 | B-field), without affecting any other component of the toolkit.
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| 121 | <p>
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| 122 | <li><b>Particle Definition and Matter</b>
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| 123 | <p>
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| 124 | These two categories manage the the definition of materials and particles.
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| 125 | <p>
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| 126 | <li><b>Physics</b>
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| 127 | <p>
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| 128 | This category manages all physics processes participating in the interactions
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| 129 | of particles in matter. The abstract interface of physics processes allows
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| 130 | multiple implementations of physics models per interaction or per channel.
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| 131 | Models can be selected by energy range, particle type, material, etc. Data
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| 132 | encapsulation and polymorphism make it possible to give transparent access
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| 133 | to the cross sections (independently of the choice of reading from an ascii
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| 134 | file, or of interpolating from a tabulated set, or of computing analytically
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| 135 | from a formula). Electromagnetic and hadronic physics were handled in a
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| 136 | uniform way in such a design, opening up the physics to the users.
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| 137 | <p>
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| 138 | <li><b>Hits and Digitization</b>
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| 139 | <p>
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| 140 | These two categories manage the creation of hits and their use for
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| 141 | the digitization phase. The basic design and implementation of the Hits
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| 142 | and Digi had been realized, and also several prototypes, test cases and
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| 143 | scenarios had been developed before the alpha-release. Volumes (not necessarily
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| 144 | the ones used by the tracking) are aggregated in sensitive detectors, while
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| 145 | hits collections represent the logical read out of the detector. Different
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| 146 | ways of creating and managing hits collections had been delivered and tested,
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| 147 | notably for both single hits and calorimetry hits types. In all cases,
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| 148 | hits collections had been successfully stored into and retrieved from an
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| 149 | Object Data Base Management System.
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| 150 | <p>
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| 151 | <li><b>Visualization</b>
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| 152 | <p>
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| 153 | This manages the visualization of solids, trajectories and hits, and
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| 154 | interacts with underlying graphical libraries (the Visualization class
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| 155 | category). The basic and most frequently used graphics functionality had
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| 156 | been implemented already by the alpha-release. The OO design of the visualization
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| 157 | component allowed us to develop several drivers independently, such as
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| 158 | for OpenGL and OpenInventor (for X11 and Windows), DAWN, Postscript (via
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| 159 | DAWN) and VRML.
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| 160 | <p>
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| 161 | <li><b>Interfaces</b>
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| 162 | <p>
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| 163 | This category handles the production of the graphical user interface
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| 164 | (GUI) and the interactions with external software (OODBMS, reconstruction
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| 165 | etc.).
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| 166 | <p>
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| 167 | </ol>
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| 168 | <P>
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| 169 | <hr>
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| 170 | <p>
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| 171 | <table>
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| 172 | <tr><td valign=top><a name="GBooch">[1]</a>
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| 173 | <td>Grady Booch, Object-Oriented Analysis and Design with Applications
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| 174 | The Benjamin/Cummings Publishing Co. Inc, 1994, ISBN 0-8053-5340-2
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| 175 | </table>
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| 176 | <P>
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| 177 | <HR><A HREF="../../../../Authors/html/subjectsToAuthors.html">
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| 178 | <I>About the authors</A></I>
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| 179 | </BODY>
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| 180 | </HTML>
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