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Description
This document defines a standard modelling language, or meta-model, for
expressing data models in the IVOA. Adopting such a uniform language for all
models allows these to be used in a homogeneous manner and allows a
consistent definition of reuse of one model by another. The particular language
defined here includes a consistent identification mechanism for model which
allows these to be referenced in an explicit and uniform manner also from other
contexts, in particular from othe IVOA standard formats such as VOTable.
The language defined in this specification is named VO-DML (VO Data Modeling
Language). VO-DML is a conceptual modeling language that is agnostic of
serializations, or physical representations. This allows it to be designed to
fit as many purposes as possible. VO-DML is directly based on UML, and can be
seen as a particular representation of a UML2 Profile. VO-DML is restricted to
describing static data structures and from UML it only uses a subset of the
elements defined in its language for describing "Class Diagrams". Its concepts
can be easily mapped to equivalent data modelling concepts in other
representations such as relational databases, XML schemas and object-oriented
computer languages.
VO-DML has a representation as a simple XML dialect named VO-DML/XML
that must be used to provide the formal representation of a VO-MDL data model.
VO-DML/XML aims to be concise, explicit and easy to parse and use in code that
needs to interpret annotated data sets.
VO-DML as described in this document is an example of a domain specific
modeling language, where the domain here is defined as the set of data and
meta-data structures handled in the IVOA and Astronomy at large. VO-DML
provides a custom representation of such a language and as a side effect allows
the creation and use of standards compliant data models outside of the IVOA
standards context.
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