[Halld-offline] Minutes of the August 10 GlueX Offline Meeting

[Mark M. Ito]

  Find the minutes posted at 
http://www.jlab.org/Hall-D/software/wiki/index.php/GlueX_Offline_Meeting%2C_August_10%2C_2010#Minutes 
and reproduced below.

GlueX Offline Meeting, August 10, 2010
Minutes

JLab: Mark Ito (chair), Richard Jones, David Lawrence, Sascha Somov,
Simon Taylor, Beni Zihlmann

Announcements

* New release, sim-recon-2010-07-28. Mark mentioned the [25]new
release, announced almost two weeks ago. No comments on usability
one way or another (no news = good news?).
* b1pi analysis in cron job. Mark showed the plots that are now
produced automatically on a weekly basis. They show momentum
distributions for positive pions, negative pions, protons and
photons as well as angular distributions for the the same set of
particles in b[1]π events. Both the script to do the reconstruction
and the ROOT macro to make the plots are from David. Mark asked
whether there was sentiment for mailing out the plots to the
collaboration for review regularly; there was not. Does not mean
that he won't do it anyway.


Review of minutes from the last meeting

* OSG Toolkit installation. The IT Division has still not opened the
ports necessary for the OSG client programs to work at the Lab.
Mark will ping them on the issue.
* Software Workshop. David reported that the proposal to the JSA
Initiatives Fund for the Software Workshop was submitted. We will
have to wait until the first part of November before we hear a
response.
+ Richard noted that he has noticed some inconsistencies in the
handling of JSA Initiative Fund proposals that include money
for experimental equipment.
* Event Display. Andrew Blackburn will give an update of his work at
the next Online Meeting.


Hall-D File Formats

David gave a overview of various event file formats, how we are using
them, and how we should be using them. See [28]his slides for the
details. The slide titles were:
* HDDM
* XML vs. C++
* EVIO
* Banks vs. C++
* Why make a HDDM to EVIO converter?
* Why not make hdgeant write Most of the software written for Hall-D
will be

based on C++ objects in memory.out EVIO formatted data?
* Why File Format is mostly a non-issue
* Arguments for switching to a single format
* Hall-D Data Flow

Discussion was wide ranging and went on for the better part of two
hours. We talked about ROOT, C++, JAVA, Service oriented architectures,
web services, object persistency, crates, slots, channels, and private
jets. The only standard topic omitted was Vaseline®.

David's position on file formats can be summarized in items from two of
his slides:
* Why file format is mostly a non-issue. Two of the bullets in this
slide state:
+ Most of the software written for Hall-D will be based on C++
objects in memory.
+ Framework was designed from day 1 to accommodate multiple
formats so that ALL DANA programs would be file format
agnostic
* Arguments for switching to a single format. These are described as
falling into two categories, "unsound" and "invalid".

As long as the objects are the primary things that we need to worry
about, a data format needs only express the information that passes
from object to object. The important thing is that messages get sent
with good fidelity, not so much how they are written. We just need to
have front-ends that understand a variety of formats.

Mark argued on the other side: that we need to be careful about how
event data is expressed outside of running programs or during
interprocess communication and further that objects in memory only
exist for a short period of time, and are usually difficult to
reproduce (weeks, months, years later) in detail. Standardization on a
format makes it possible for other tools to be used to analyse the same
data using a different set of objects or even a different language. In
this view the objects operate on the data and are not the fundamental
"things".

In summary the conflict is between a data-centric vs. object-centric
view. HDDM represents a data-centric view. JANA represents a
object-centric view. We did not resolve which philosophy we should
adopt as collaboration policy.

New Action Items

1. Ping IT Division on Globus ports -> Mark

Retrieved from
"http://www.jlab.org/Hall-D/software/wiki/index.php/GlueX_Offline_Meeting%2C_August_10%2C_2010"

References

25. https://mailman.jlab.org/pipermail/halld-offline/2010-July/000335.html
28. 
http://www.jlab.org/Hall-D/software/wiki/images/8/82/20100810_fileformat.pdf