Athena Developer Guide

Athena Appendix C Design considerations Version/Issue: 2.0.0
because they can be used by a range of different algorithms. We could have various types of tracking
algorithm all using the same data as input and producing similar data as output. On the contrary, the
intermediate data types can be designed to be very algorithm dependent.
The way we have chosen to communicate between the different Algorithms which constitute our
physics algorithm is by using the transient event data store. This allows us to have low coupling
between them, but other ways could be envisaged. For instance, we could implement specific methods
in the algorithms and allow other “friend” algorithms to use them directly.
Concerning the relationships between data objects, it is strongly discouraged to have links from the
input data objects to the newly produced ones (i.e. links from hits to tracks). In the other direction this
should not be a problem (i.e from tracks to constituent hits).
For data types that we would like to save permanently we need to implement a specific Converter. One
converter is required for each type of data and each kind of persistency technology that we wish to use.
This is not the case for the data types that are used as intermediate data, since these data are completely
transient.
C.4.3 Mathematics and other utilities
It is clear that to implement any algorithm we will need the help of a series of utility classes. Some of
these classes are very generic and they can be found in common class libraries. For example the
standard template library. Other utilities will be more high energy physics specific, especially in cases
like fitting, error treatment, etc. We envisage making as much use of these kinds of utility classes as
possible.
Some algorithms or algorithm-parts could be designed in a way that allows them to be reused in other
similar physics algorithms. For example, perhaps fitting or clustering algorithms could be designed in a
generic way such that they can be used in various concrete algorithms. During design is the moment to
identify this kind of re-usable component or to identify existing ones that could be used instead and
adapt the design to make possible their usage.
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