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The CWM Foundation, in its DataTypes package, provides metamodel types supporting definition of data types required by data
sources, data targets, and tools that implement transformations between them. Although these metamodel types are sufficient
to permit the definition of most data types, they do not themselves actually create definitions of data types. This is because
the metamodel types are M2 level types whereas data type definitions are M1 level definitions.
This approach to the creation of data types was chosen because the specific data type needs of individual transformation tools
and source and target data systems are sufficiently different that their interchange cannot be specified fully in advance.
Unfortunately, data type incompatibility is often true even for systems that claim to support the same data language (consider,
for example, the many variants of “SQL?).
Even though some tools and systems may enjoy compatibility for commonly used data types (such as integer and string), systems
that are compatible across the full range of their data types are indeed rare.
Data type incompatibilities between systems result from a number of factors including specific characteristics of hardware
implementation platforms, software vendors’ desire to differentiate their products in the marketplace, and other, largely
historical, causes. These factors combine to make definition of a common set of data types supporting the diverse, and frequently
incompatible, needs of existing and future CWM-compliant tools impossible in any practical way. Consequently, modelers of
software systems in CWM may find it necessary to create both data type definitions compatible with their tools and to create
TypeMapping instances to indicate mappings between their tools’ data types and the native data types of systems with which
they interchange data.
Nevertheless, the CWM recognizes the importance of shared data types -- especially those based on industry standards such
as CORBA IDL, SQL and Java -- as a means of promoting data interchange between disparate systems. Consequently, this chapter
provides a set of data type definitions for several widely used industry specifications. These data type definitions serve
two purposes within the CWM:
• Provide a pre-defined basis for data interchange among diverse tools and systems that support a selection of standard data types.
• Provide examples of the appropriate use of the CWM Foundation’s metamodel types for creating tool-specific data type definitions.
To further promote understanding of the appropriate use of other CWM Foundation metamodel types, this chapter also contains
examples showing how tool-specific expressions can be mapped into the CWM Foundation’s expression metamodel types.
In general, the CWM packages only support data type attributes that are considered necessary for interchange of information
between systems; attributes that are thought to be system specific are left to tool modelers. When such attributes must be
represented, modelers may create model-specific types that derive from supplied CWM types and house the necessary attributes
therein.
The information and definitions in this chapter, while considered important to accomplishing the overall goals of CWM, are
supplementary in nature and are not considered a normative part of the CWM specification.