====== HDF5 File Format Meeting ======

Location & Date:
    * University of Amsterdam, The Netherlands
    * September 9-10, 2010

Overview: 
    * Quincey Koziol from the HDF5 Group visited the LOFAR crew at the UvA on Thursday-Friday (Sept. 9-10th).  The agenda is listed below.  We gave Quincey an overview of LOFAR along with an introduction to the LOFAR data format/structures from the Interface Control Documents (ICDs).  All presentations are attached below. Quincey's HDF5 presentations can also be found below.


Participants:
   * HDF5 Group Member - Quincey Koziol
   * Attendees - Anastasia Alexov, Ken Anderson, John Swinbank, Lars Baehren, Micheal Wise, Adriaan Renting, Ger van Diepen, Tom Bennett (South Africa via EVO)

==== Agenda ====
Thursday 10AM-lunch:
   * LOFAR Overview (15-30 mins) - Swinbank, {{Swinbank-HDF5-LOFAR.pdf|An Introduction to LOFAR}}
   * LOFAR Image cubes (15-30 mins) - Anderson, {{LOFAR_HDF5_SkyImage.ppt|LOFAR Sky Image Cubes}}
   * (coffee break @11AM)
   * LOFAR Beam-formed data (15-30 mins) -  Alexov, {{LOFAR-HDF5_BFoverview_20100909.ppt|LOFAR Beam-Formed Data & Pipeline Overview}}
   * LOFAR Coordinates (15-30 mins) -  Baehren, {{2010-09-09-DAL.pdf|The Data Access Library ([[engineering:software:tools:DAL]])}}
   *(lunch)

Thursday 2PM-5PM:
   * HDF5 talk/tutorial (60 min)  -  Quincey Koziol
   * Discussion on questions/concerns listed below  - All

Friday 10AM-lunch:
   * Performance questions (15-30 mins) - van Diepen, {{hdf5-casacore.ppt|HDF5 and casacore}}
   * Open discussion on performance
   * (coffee break @11AM)
   * HDF5/LOFAR-related questions - All
   * (lunch)

Friday 2PM-5PM:
   * Open discussion - All

==== HDF5 Presentations ====

    * {{HDF5_Introduction1_Model.ppt|Introduction to HDF5}}
    * {{HDF5_Introduction2_Format.ppt|Introduction to HDF5 - Session Two - Data Model Comparison; HDF5 File Format}}
    * {{HDF5_Introduction3_Software.ppt|Introduction to HDF5 - Session Three - HDF5 Software Overview}}
    * {{HDF5_Introduction4_Java.ppt|Introduction to HDF5 - Session Four - Java Products}}
    * {{HDF5_DataValuesAreKey.ppt|Introduction to HDF5 - Session Five - Reading & Writing Raw Data Values}}
    * {{HDF5_Introduction-Datatypes.ppt|Introduction to HDF5 - Session Seven - Datatypes}}
    * {{HDF5_Introduction-IOPerformance.ppt|Introduction to HDF5 - High Performance I/O}}
    * {{HDF5_Introduction-Math.ppt|Introduction to HDF5 - Introduction to Mathematical Concepts}}
    * {{HDF5_Introduction-StorageOptions.ppt|Data Storage and I/O in HDF5}}
    * {{HDF5Update.ppt|HDF5 Update}}

==== QUESTION/TOPIC for DISCUSSION: ====
   * performance benchmarks
   * access patterns
   * intelligent filtering and slicing
   * efficient data storage / chunking
   * parallel I/O
   * distributed storage
   * tools which exist for HDF5 (other than HDFView, h5py, pytables)

==== CONCERNS: ====
    * Speed when using smallish hyperslabs
    * Robustness. E.g. What happens if a system crashes after writing some hours of data? What are the chances that all data are lost? What impact has robustness on performance?
    * The future of the C++ interface.
    * Is HDF5 always backward compatible? I.e. can a file created with HDF5 1.8 always be read with newer versions, even a hypothetical version 2.1 (AFAIK HDF5 1.8 is not backward compatible with 1.6). The same for building the software.
    * Is it more efficient to store data in:
     - One table per subband (N x 1-dimensional tables in one Group)
     - One table for all subbands (1 x N-dimensional table in one Group) 
     - 1 Array per Subband (N x 1-dimensional array in one Group)
     - 1 Array for all Subbands (1 x N-dimensional array in one Group)


=== LOFAR ICD (Interface Control Documents): ===

LOFAR Interface Control Documents (ICDs): [[http://usg.lofar.org/wiki/doku.php?id=documents:lofar_data_products]]