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Lemson, G., Dowler, P., & Banday, A. J. 2003, in ASP Conf. Ser., Vol. 314 Astronomical Data Analysis Software and Systems XIII, eds. F. Ochsenbein, M. Allen, & D. Egret (San Francisco: ASP), 472

A Unified Domain Model for Astronomy

Gerard Lemson
Max-Planck-Institut für extraterrestrische Physik, Garching, Germany

Patrick Dowler
National Research Council Canada, Victoria, BC, Canada

A. J. Banday
Max-Planck-Institut für Astrophysik, Garching, Germany


We propose a framework for constructing a unified, conceptual domain model for astronomy. We believe such a model to be an essential ingredient for a future Virtual Observatory (VO). We also give a high level, skeleton proposal for this VO domain model. We indicate where details must be filled in for more specialized models. We describe one detailed base level model, a component model for Quantity, which is a generalisation of previous informal proposals. Our domain model puts it in a larger context that includes such concepts as measurement, error, and units.

1. Introduction

Standard methodologies (see Fowler 1997, Booch 1994, Halpin 2001) identify various phases in the software development process. The first phase analyses the universe of discourse (UoD), that is the world that we are interested in talking about in the context of a particular project (Halpin 2001). The goal is to come to a comprehensive domain model containing all the relevant concepts and their interrelations. There are reasons why such a model is an essential ingredient for the development of a Virtual Observatory (VO). It will provide a common grammar and vocabulary for expressing the varied data products existing in distributed astronomical databases. It will define the set of concepts that a user of the VO can use in queries to these archives. Without such a common, ``Esperanto'' data model it will not be possible to achieve true interoperability between different archives. In different terms, we believe the conceptual model arising from the standard analysis phase to be equivalent to an ontology.

2. Modelling Domain

We define the UoD for the VO as ``the work that astronomers, astrophysicists and support scientists do and the results they have obtained''. Our motivation for this choice is that we believe that users of the VO are ultimately interested in the results of the work done by other astronomers. Users are not ``just'' interested in getting access to images, simulation results or other physical results of astronomical research, stored in some astronomical archive, but will want to know what is actually represented by these results, how they were obtained, what experiments were executed and how. The latter is what we mean by the term ``work''.

When we say that we believe VO users will be interested in the experiments that produced the results, we mean that they should be interested in them. One of the main tasks of the VO is to enable other astronomers to do rigorous science with the results and services that are made available through it by their colleagues. It is obvious that results can only be interpreted through knowledge of the process that produced the results - the ``provenance''. We believe the VO has both the chance and duty to formalize the concepts underlying this provenance by including them explicitly in the modelling effort.

3. Modelling Concepts

Here we list some of the core concepts we believe need to be modelled explicitly to give a proper description of the world of astronomy, the UoD of the VO. In the full model (, these have been translated into UML classes and worked out in more detail.

Figure 1: A detail of the domain model, dealing with measurements and values.

4. Model Detail: Measurement and Quantity

Modelling quantitative values with units and errors has received considerable attention in the IVOA data modelling working group. In Figure 1 we propose a model for this area. The main difference between this and other proposals (see for IVOA Quantity data modeling resources ) is that we believe that the core concept is the measurement, which we define as the act of assigning a value plus error to a property, not the quantity itself. We further generalize the Quantity concept to values and classifiers. To see how this model fits within the large scale framework we refer the reader to the full diagram (


This work was undertaken as part of a Canadian Virtual Observatory (,
CVO) and German Astrophysical Virtual Observatory (, GAVO) collaborative research project. CVO is sponsored by the National Research Council (NRC) and the Canadian Space Agency (CSA). GAVO is sponsored by the German Federal Ministry for Education and Research (BMBF).


Grady Booch 1994, Object-oriented Analysis and Design, 2nd edition, Addison-Wesley

Martin Fowler 1997, Analysis Patterns, Addison-Wesley

NIST 1999, SI Specification,

Terry Halpin 2001, Information Modelling and Relational Databases, Morgan Kaufmann

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