Common Warehouse Metamodel in EMF
The Common Warehouse Metamodel (CWM) is a standard
by the Object Management Group (OMG).
The intention of CWM is to define a standard for metadata in Data Warehouses and
Business Intelligence applications.
CWM uses the Meta Object Facility (MOF)
as the underlying framework.
MOF is also used in other standards of the OMG,
for example UML.
My intention was to learn about CWM and it is very difficult to learn a data model by studying the
specifications on paper. I wanted an interactive editor.
But i did not find an open source editor in the net. I found a MOF complient database,
the Metadata Repository (MDR) (note 2011: no longer available),
but it does not have an editor.
So i decided to transform the CWM/MOF model to EMF and generate an editor from it.
The editor is in an early, but it is already usable for experiments and for learning CWM.
Mapping MOF to EMF Ecore
In [1,2] a mapping between MOF and EMF is described. These articles served as a starting point, but i did
not find the E-MORF software described in one of these articles on the net. Therefore i wrote an XSLT
transformation that implements the following mapping of MOF elements to EMF elements.
| MOF Element |
EMF Element |
EMF Tag |
| XMI.content |
ecore:EPackage |
ecore:EPackage |
| Model:Attribute |
ecore:EReference or ecore:EAttribute |
eStructuralFeatures |
| Model:Class |
ecore:EClass |
eClassifiers |
| Model:DataType |
ecore:EEnum or ecore:EDataType |
eClassifiers |
| Model:Package |
|
eSubpackages |
| Model:Reference |
ecore:EReference |
eStructuralFeatures |
I transformed the CMW 1.1 XML specification into an Ecore/EMF model.
The following screenshot shows a small extract of the resulting EMF ecore model.
An editor plugin for CWM in EMF
From the ecore model i generated an EMF Editor. The following screenshot shows the "New Wizard".
You can see that there is a model for every subpackage of CWM. The "CWM Model" is the best choice most of
the time.
The next screen shows the subpackages available and the complexity of CWM. In this example the
"relational container is chosen".
The relational package is used for information on objects in relational databases. In the next screenshot the
elements available are shown.
The editor is available per request.
There are a number of open issues.
-
The mapping from MOF to Ecore/EMF is not implemented bidirectional. That means, there is no
"Export as CWM/MOF" functionality.
-
The Ecore/EMF model should be as simple as possible. In MOF references between two classes are modeled as
reificated
Model:Association classes and these contain the referenced classes. These are
transformed to the Ecore/EMF references.
-
The CWM data model is very general in the sense that many classes are derived from the basic class
Core.ModelElement. And references often use classes that are very general and very high in
the class hierarchy. This complicates the usage of CWM in an editor.
References
Copyright © 2007-2012 Jörn Dinkla. All rights reserved.
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