C++ / G4MICE Course

Session 7

Models vs RepresentationsPersistency

Real Data FormatsReader

Models vs Representations• So far we have been making models of various

experiments using the MiceModule class.• When we run the simulation, event display,

reconstruction, etc, some information from the model is required.

• This information needs to be supplied in a manner appropriate to the use of the model (e.g. GEANT4 vs RecPack)

• To solve the potential problem of having the modelling code depend on every potential use that it could be put to, we make the distinction between models and representations.

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If We Only had a Model

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Model

GEANT4

RecPackHepRep

ROOT

Reconstruction

SimulationEvent Display

With Representations

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Model

GEANT4

Simulation

Simulation Representation

RecPack

Reconstruction

Reconstruction Representation

G4MICE Representations

• Simulation:– DetModel and EngModel– Take the MiceModule model and create the

necessary G4 objects

• Reconstruction:– SetupKalman (Recon/SciFi)

• Event Display:– Visualization– Uses HepRep XML writer.

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“The Data”

• When using G4MICE or writing use applications, we don’t think about the data files or the data formats.

• The data exists in instances of various classes (e.g. SciFiHit, VlpcHit, etc...)

• So when you want to find “some data” what you really need to do is work out what class(es) represent that data and what method(s) can provide it.

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Persistency

• The classes that represent the data only exist in the computer’s memory while the program is running – they are transient.

• We want to store the classes in some format so that they can “live” beyond the execution of the program – make them persistent.

• This can involve writing them to disk, to a database, ...

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Gzipped Text File• The current persistency method that is

implemented is a gzipped text file.• The Zlib library is used to perform zipping and

unzipping as the files are written or read.• The format is plain text so can be read for

debugging purposes.• You should never write your own code to read

this (or any other format) file unless you are specifically involved in the development of the persistency code.

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Persistency Design

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Transient Class(e.g. SciFiHit)

Gzipped Text File

SciFiHitTextFileIo

MySQL

SciFiHitMySQL

Real Data Formats• We currently have code that reads a

number of other specific file formats associated with different DAQs that have been used in MICE to date:– KEK test beam (2 different formats)– Tracker test with Visual Basic (2 different

formats)

• Work is in progress to implement the code to read in the DATE format files and produce the relevant classes.

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Reader• All of the classes that read the various file formats

(whether persistent text file, or test beam or other DAQ formats) are derived from a purely virtual base class called Reader.

• It requires all the derived classes to implement a few methods:– readEvent()– isOK()– closeInputFile()– skipEvents()

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Code Inspection• Have a look at:

– Interface/include/Reader.hh– Persist/textFile/include/TextFileReader.hh– RealData/include/VlsbReadout2006.hh

• See how each of the classes implements a version of (a kind of!) the Reader class.

• See how this is used in:– Applications/common/GlobalReader.hh– Applications/KekOct2005/Kek2005.cc– Applications/KekOct2005/cards.in

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Remaining Time this Session

• Continue work on the MuScat modelling and simulation assignment...

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