Athena Developer Guide

Athena Chapter 14 Tools and ToolSvc Version/Issue: 2.0.0
information is stored. For some specific Associators, in addition, it can depend on some algorithmic
choices: consider as an example a physics analysis particle and a possible originating Monte Carlo
particle where the associating discriminant could be the fractional number of hits used in the
reconstruction of the tracks. An advantage of this approach is that the implementation of the navigation
can be modified without affecting the reconstruction and analysis algorithms because it would affect
only the associators. In addition short-cuts or complete navigational information can be provided to the
user in a transparent way. By limiting the use of such associators to dedicated monitoring algorithms
where the comparison between raw/reconstructed data and MC truth is done, one could ensure that the
reconstruction and analysis code treat simulated and real data in an identical way.
Associators must implement a common interface called IAssociator. An Associator base class
providing at the same time common functionality and some facilities to help in the implementation of
concrete Associators is provided. A first version of these classes is provided in the current release of
Athena.
14.4.1.1 The IAssociator Interface
As already mentioned Associators must implement the IAssociator interface.
In order for Associators to be retrieved from the ToolSvc only via the IAssociator interface, the
interface itself inherits from the IAlgTool interface. While the implementation of the IAlgTool
interface is done in the AlgTool base class, the implementation of the IAssociator interface is the
full responsibility of concrete associators.
The four methods of the IAssociator interface that a concrete Associator must implement are show
in Listing 14.7
Listing 14.7 Methods of the IAssociator Interface that must be implemented by concrete associators
1: virtual StatusCode i_retrieveDirect( ContainedObject* objFrom,
ContainedObject*& objTo,
const CLID idFrom,
const CLID idTo ) = 0;
2: virtual StatusCode i_retrieveDirect( ContainedObject* objFrom,
std::vector& vObjTo,
const CLID idFrom,
const CLID idTo ) = 0;
3: virtual StatusCode i_retrieveInverse( ContainedObject* objFrom,
ContainedObject*& objTo,
const CLID idFrom,
const CLID idTo) = 0;
4: virtual StatusCode i_retrieveInverse( ContainedObject* objFrom,
std::vector& vObjTo,
const CLID idFrom,
const CLID idTo) = 0;
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Two i_retrieveDirect methods must be implemented for retrieving associated classes following
the same direction as the links in the data: for example from reconstructed particles to Monte Carlo
particles. The first parameter is a pointer to the object for which the associated Monte Carlo