CWM Data Types 19 Contents This chapter contains the following topics. Topic Page “Overview” 19-1 “Organization of the CWM Data Types” 19-2 “CORBA IDL Data Types” 19-3 “J ava Data Types” 19-10 “SQL-99 Data Types” 19-11 “Type Mapping Examples” 19-15 19.1 Overview 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”). October 2001 Common Warehouse Metamodel, v1.0 19-1 19 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. 19.2 Organization of the CWM Data Types The CWM DataTypes contains definitions of data types for the CORBA IDL language [CORBA], the SQL-99 language [SQL], and the Java programming language [Java]. Because they are M1 level entities, data type definitions for these languages are expressed in a tabular form that indicate the instances of M2 level CWM metaclasses that can be created in an appropriate CWM metadata store to define the M1 level data types. The data type definitions might then be used to create M1 level models appropriate for specific tools and software systems. 19-2 Common Warehouse Metamodel, v1.0 October 2001 19 The example M1 instances define only primitive data types; structured data types are not generally defined in these examples. (However, the CORBA IDL metamodel types required to define M1 structured types are provided as an example of how this might be done, if needed.) Data types that require no additional information to complete their definition, such as SQL’s INTEGER type, are completely defined. However, data types that are in some sense “parameterized,” such as SQL’s CHARACTER(n) and FIXED(p, s) data types, are incompletely defined because it is not practical to anticipate all possible parameter values! Tools that need to declare such parameterized data types should do so as they encounter them. The data type instances in this chapter define a few parameterized data types, where appropriate, as examples. As an example of appropriate usage of the CWM Foundation’s TypeMapping metamodel to indicate preferred and non-preferred mappings between the data types of different tools and software systems, the last section of the chapter contains some example mappings between Java and CORBA IDL and between Java and SQL-99. 19.3 CORBA IDL Data Types The CORBA IDL Data Types package depends on the following packages: • org.omg::CWM::ObjectModel::Core • org.omg::CWM::Foundation::DataTypes 19.3.1 Overview A CORBA IDL metamodel extension to the CWM Foundation is required to support the CORBA IDL data types in the CWM model. It is provided here as an example of extending the DataTypes metamodel and is not a normative part of the CWM specification. The chief motivation for the creation of this metamodel is the need to provide a typeCode attribute for CORBA IDL data types. These extensions also serve as an illustration of the use of CWM Foundation metamodel types as superclasses of the metamodel types for a specific language environment. 19.3.2 Organization of the CORBA IDL Data Types Because the M1 data type instances are of primary import and because of the length of the metamodel subsection, the M1 instances are described before the metamodel types. When reviewing the M1 instances, refer to the appropriate metamodel type definitions and Figure 19-1 for more information about metamodel types. October 2001 OMG-CWM, v1.0: CORBA IDL Data Types 19-3 19 DataType (f rom Core) elementType IDLType typeCode : TypeCode TypeAlias Enumeration Uni on (f rom DataTy pes) (f rom DataTy pes) (from DataTypes) 1 1 elementType * * ArrayT ype SequenceType StringType Alias EnumT ype UnionType length : Integer length : Integer / elementType : IDLType / elementType : IDLType length : Integer E x ce p ti on T yp e StructType WstringType FixedType length : Integer digits : Integer scale : Integer Figure 19-1 CORBA IDL data type metamodel types 19.3.3 CORBA IDL Data Type Instances Data type instances for CORBA IDL non-structured data types are presented in the following table. The M1 data types instances correspond to those described in the CORBA IDL language specification. CORBA IDL Instance of Attributes Data Type any IDLType typeCode = tk_any octet IDLType typeCode = tk_octet boolean IDLType typeCode = tk_boolean char IDLType typeCode = tk_char wchar IDLType typeCode = tk_wchar short IDLType typeCode = tk_short long IDLType typeCode = tk_long long long IDLType typeCode = tk_longlong unsigned short IDLType typeCode = tk_ushort unsigned long IDLType typeCode = tk_ulong unsigned long long IDLType typeCode = tk_ulonglong 19-4 Common Warehouse Metamodel, v1.0 October 2001 19 CORBA IDL Instance of Attributes Data Type float IDLType typeCode = tk_float double IDLType typeCode = tk_double long double IDLType typeCode = tk_longdouble 19.3.4 CORBA IDL Data Types Classes CORBA IDL metamodel classes are provided to support the definition of CORBA data types that cannot be represented simply as instances of the IDLType class. This group of types includes all CORBA structured and array-like data types as well as those that also derive from the types defined in the CWM Foundation’s Data Types conceptual area. 19.3.4.1 Alias The Alias type represents CORBA IDL type aliases. Aliases must be represented by their own type so that they can have a typeCode attribute as required by the CORBA IDL definition. Superclasses IDLType TypeAlias 19.3.4.2 ArrayType The ArrayType class represents CORBA IDL array data types. Superclasses IDLType Attributes length The number of elements in the array. Multiply dimensioned arrays are treated as arrays of array in CORBA IDL. type: Integer multiplicity: exactly one October 2001 OMG-CWM, v1.0: CORBA IDL Data Types 19-5 19 References elementType The type of elements of an array. class: IDLType defined by: ArrayElementType::elementType multiplicity: exactly one 19.3.4.3 EnumType The EnumType class represents the CORBA IDL enumerated data type, enum. Superclasses IDLType Enumeration 19.3.4.4 ExceptionType The ExceptionType class represents the CORBA IDL exception data type. Superclasses IDLType 19.3.4.5 FixedType The FixedType class represent CORBA IDL fixed data types. Superclasses IDLType Attributes digits Number of digits of precision. type: Integer multiplicity: exactly one 19-6 Common Warehouse Metamodel, v1.0 October 2001 19 scale Number of implied decimal places. Scale may be either positive (implied left decimal places) or negative (implied right decimal places). type: Integer multiplicity: zero or more 19.3.4.6 IDLType The IDLType class is a common superclass for all CORBA IDL data type classes that require a typeCode. Superclasses DataType Attributes typeCode The type code value identifying a CORBA IDL data type. type: TypeCode multiplicity: exactly one 19.3.4.7 SequenceType The SequenceType class represents CORBA IDL sequence data types. Sequences are single dimensioned arrays of a user-specified type. Superclasses IDLType Attributes length The number of elements in the sequence expressed in type units.