Event model: Concepts

D. Adams
27sep01 1340

We have already introduced most of the concepts behind the event model. Here we list them with brief definitions.

Global event

An event is all the data associated with a triggered crossing or Monte Carlo simulation thereof. This data includes a collection of EDO's and the history for each.

Local event

This is collection of EDO's and their histories from an event. It differs from an event in that has a subset of the EDO's. These might be the EDO's produced before a certain date, those from the last production or those presently available on disk.

We can avoid data duplication and keep a full reconstruction chain by having an event point to its parent event when a new event is used to add data to an existing event. This is called a local event chain.

I believe the events in the ADB (ATLAS database model) are local events.

Event data object (EDO)

This a piece of data from the event, typically a collection of physics data objects (tracks, jets, electrons, etc). The raw data for an event is another type of EDO. The remaining EDO's are derived from this. Each of the derived EDO's is the output of an algorithm.

I believe that EDO's correspond to data objects in StoreGate. ADB sharing categories are similar but appear to refer to a collection of EDO's from the same processing step of the same event.

EDO history

The history of an EDO serves to document its existence. It can be used to select a particular EDO. It should be sufficient to rebuild that EDO. Note that typically most or all of an EDO history will be shared by many EDO's.

Physics data object (PDO)

These are the fundamental objects which make up our data. Examples include clusters, tracks, jets, electrons and Z's. EDO's are usually collections of such objects. For event data, each of objects are is contained in exactly one EDO. These objects are able to refference one another via links. The references can cross EDO boundaries but not event boundaries.

Event collection

This is a collection of associated events. They may be sequential events in DAQ stream or may be Higgs candidate events.

Link

A link allows a PDO in one EDO to reference a PDO in another. These links can only point to data which existed when the link was being created and so can point in only one direction unless the same algorithm creates both EDO's.

dladams@bnl.gov