The ALMA Science Data Model

New aspects with ALMA:

The Science Data Model:


Some technical design properties:

Design strategy:

Whatever the language used, the strategy is the same, Decomposing too much a problem may lead to poor performances.

It may be necessary to find compromizes:
Adopted design:
Some technical detail about implementations:
Archiving in XML

Contexts and Perspectives:

The model is intended for radio-telescopes in general (single-dish, interferometers).

It is migrating from the ALMA SDM (ASDM) to the SDM (the plan is to use it for the eVLA).

Toward a standard for the radioastronomy? (VO?).

The ALMA project must be able to provide data using an export data format (TBD).

Extension of the data model for the heuristics and data analysis:

The SDM can be considered as a classic relational model:
R&D is required to extend the SDM to be able to manage the informations contained in the astronomical data themselves at the level of the database itself.

The most direct approach is to search for schemes in the Fourier domain for the cross-correlations for the observed visibilities and the image-plane for the auto-correlations.

It requires extending the relational model for similarity queries (as opposed to exact matching) to be able to handle scoring functions.

For some schemes extensive simulations will be required to help understanding the high level of abstraction in the data characterization.


Example using the brightness distribution of a simulated compressive turbulence

Consider the distribution of the phase increments and define the entropy in its distribution:

The entropy for a Kolmogorov distribution is:

The amount of structure present in the distribution could be defined by:

The histogram of the phase increment can be fitted by a van Mises distribution:

In this context this quantity of structure is given by (F. Levrier):

and we may consider to introduce this as an attribute of the data model, a property of the cross-correlation data themselves at some level in the project structure.

Francois Viallefond
Last modified: Wed May 11 12:34:40 CEST 2005