ATLAS Distributed Computing Tutorial

Hands-on Session 1, Part 3: Using Tags

Introduction
Pre-Tutorial Exercises
Part 1: Accessing Tags using POOL Collection Utilities
Part 2: Using Tags directly with Athena
Part 3: Using Tags with TNT
More Information

Introduction

The ATLAS Tag system is intended to be an event-level metadata system, allowing efficient identification and selection of events of interest for a given analysis. The expectation is that, in practice, first-level cuts will be possible (and could greatly reduce candidate sample sizes) via queries that are supportable in relational databases. The nominal space budget for the TAG in the Computing TDR is 1 KB/event. The Tag is to be producible from AOD, though Tag databases contain or are linked to sufficient navigational information to allow retrieval of event data at all production processing stages, i.e., AOD, ESD, Raw Data (RDO).

Tags are initially produced from merged AOD files, in ROOT format. These ROOT files are later loaded into a central Tag database at Tier 0 which will be replicated to Tier 1 and 2 sites. The original ROOT files are kept, which means there are two formats in which the Tag data exists:

  • ROOT: ordinary ROOT files, which can be opened in ROOT
  • Relational: Tag data stored in a relational database, currently either MySQL or Oracle

    • During this part of the tutorial, then, reference will be made to both 'ROOT-based Tags' and 'Relational Tags'.

    This part of the tutorial will explore some aspects of using the Tag, but there is insufficient time to go into much depth. Each section, described below, will therefore include a 'More information' area with links to useful documents or exercises for further reading. The aim is therefore to lay some ground-work for using Tags in your analysis by building familiarity with the system rather than giving step-by-step instructions of "how to do analysis with Tags".

    Pre-Tutorial Exercises

    It is very important that the following steps are done before arriving at the tutorial. The time schedule for the tutorial exercises is quite tight and there will be no time to fix problems with the setup.

  • Make sure you have a valid grid certificate
  • Log onto an SLC3 node on lxplus: 
    ssh lxslc3.cern.ch
    For this tutorial, SLC3 nodes will be used - the grid user interface and various other pieces of software are not yet SLC4-ready.
  • Prepare your home area on lxplus to use the ATLAS software, with version 12.0.4. This is detailed in the ATLAS Workbook at Setting up your Account. If you are not already using release 12.0.31 or higher, please make sure that everything is working correctly by following some of the examples in the Workbook.
  • Source your grid environment using the following script: 
    source /afs/cern.ch/project/gd/LCG-share/previous/etc/profile.d/grid_env.sh
    Please use this rather than any previous grid setup script you may have been using. This is a workaround while problems associated with the SLC3/4 changeover are resolved.

  • ALSO set up your cmt: 
    source ~/cmthome/setup.sh -tag=12.0.4
  • Install TNT, the ATLAS TagNavigatorTool, using the instructions on its wiki page in the "Installing TNT" section. For this tutorial, rather than downloading the tarball from the wiki, please copy it from 
    /afs/cern.ch/user/n/nicholc/public/tutorial/tnt.tar
    and likewise get the CollSplitByGUID executable from 
    /afs/cern.ch/user/n/nicholc/public/tutorial/CollSplitByGUID.exe
    Verify that the script runs OK when you type 
    ./TNT.py -h
    in the installation directory. It should give this help message: 
    Usage: TNT.py [-h | --help] [-v | --verbose] [-c | --conf configuration file] [-b | --background] [-a | --archive]
    Don't worry about messages warning you about a 'Python C API version mismatch for module _lfc'; it is still working correctly.

    The rest of the exercises, below, will be done during the tutorial.

    Tutorial Exercises

    Part 1: Accessing Tags using POOL Collection Utilities

    This section introduces some POOL tools which can be used to manipulate Tags and explore their features before starting an analysis.

    Part 2: Using Tags directly with Athena

    This section illustrates the use of Tags for event selection with Athena.

    Part 3: Using Tags with TNT

    This section introduces TNT, a Tag Navigator Tool for ATLAS, and explores its usage.

    More Information

  • The Use Case document defines and discusses the Tags with their various use cases, and is useful for background information
  • The TagForEventSelection wiki gives a good overview of how to use Tags
    • Caitriana Nicholson
    Last modified: Fri Feb 9 17:34:08 GMT 2007