1. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 TDS objects and Converters. (Transient Data Store) Ian Gable Software Workshop Jan 2001

2. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable2 The TDS What is the TDS? A Gaudi mechanism for quickly and easily manipulating data objects. It boils down to a method of storing pointers to objects in a tree structure reminiscent of any file system. You could store raw data in a part of the tree /Event/Raw/CsIEvents And then store MC Events in another: /Event/MC/McHits Once you have an object in the TDS, it’s possible to make it persistent with very little extra difficulty. The persistency mechanism in our case is ROOT.

3. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable3 What is a TDS object? As the name suggest a TDS object is an object that plugs into the TDS To be a TDS object a class must inherit from the Gaudi class DataObject or CaintainedObject. The class must also have certain features that will allow it to work with the TDS The easiest thing to do is to show example Class:

4. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable4 Example TDS Class #ifndef TDCSI_DATA_H #define TDCSI_DATA_H 1 extern const CLID& CLID_MyClass; class MyClass : virtual public DataObject { public: virtual const CLID& clID() const { return MyClass::classID(); } static const CLID& classID() { return CLID_MyClass; } MyClass (); ~MyClass (); //!number of hit towers in the layer layer=0.. int getNumber (){ return someNumber }; //!energy recorded in the ith tower float getLongNumber() { return longNumber };

5. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable5 //! Serialize the object for reading virtual StreamBuffer& serialize( StreamBuffer& s ); //! Serialize the object for writing virtual StreamBuffer& serialize( StreamBuffer& s ) const; //! Fill the ASCII output stream virtual std::ostream& fillStream( std::ostream& s ) const; private: int m_someNumber; double m_longNumber };

6. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable6 //################################################################ // MyClassSerializeFunctions //################################################################ //! Serialize the object for writing inline StreamBuffer& MyClass::serialize( StreamBuffer& s ) const { DataObject::serialize(s); return s << m_someNumber << m_longNumber ; } //! Serialize the object for reading inline StreamBuffer& MyClass::serialize( StreamBuffer& s ) { DataObject::serialize(s); return s; >> m_someNumber >> m_longNumber ; }

7. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable7 The EventModel After setting up the object one needs to make an addition to the Glast EventModel –The event model records the Structure of the TDS Here’s our current EventModel: class EvModel { public: EvModel() { // The whole GLAST event EventModel::Event = "/Event"; // set up the MC structure EventModel::MC::Event = EventModel::Event + "/MC"; EventModel::Irf::Event = EventModel::Event + "/Irf"; EventModel::Irf::IrfAcdHits = EventModel::Irf::Event + "/IrfAcdHits"; EventModel::Irf::IrfCalHits = EventModel::Irf::Event + "/IrfCalHits"; EventModel::Irf::IrfTkrHits = EventModel::Irf::Event + "/IrfTkrHits"; EventModel::Raw::Event = EventModel::Event + "/Raw"; EventModel::Raw::TdCsIDatas = EventModel::Raw::Event + "/TdCsIDatas"; EventModel::Raw::TdSiDatas = EventModel::Raw::Event + "/TdSiDatas"; } };

8. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable8 Converters In terms of Gaudi a converter is a class that works with the TDS to transform objects from one representation to another. Converters become associated with TDS objects such that after a TDS object is matched with the appropriate converter only one line is needed to load the object –SmartDataPtr m_tdsObj(eventSvc(), “/Event/Sublevel/TDSObjects”) Once the above call is made the TDS checks to see if there is a pointer to an object in memory and if does not exists the appropriate converter is called to bring the object to life. An object can be loaded from whatever persistent form it exists in or it can be made from transforming another object.

9. GLAST LAT Offline SoftwareWorkshop - SLAC, Jan. 16-19, 2001 Ian Gable9 Things to come away with TDS objects are easy to create and fit into the existing Gaudi GLAST frame work. Converters are very versatile. Once implemented a TDS object is simple to use. One line loading of an object which the end user doesn’t need to think about. It just happens. For more information please see the GLAST Gaudi home page. Linked from Software home Have a look at my document Making TDS objects and Converters http://www-glast.slac.stanford.edu/software/Gaudi/starting_point/tdsobjects.htm