XML, Messaging and Business Transactions Component
This column is adapted from the book Universal Meta Data Models by David Marco and Michael Jennings, John Wiley & Sons.
I n this final installment of my seven-part series on component areas of the complete meta data model managed meta data environment (MME), we conclude our examination of the complete meta data model with the XML, messaging and business transactions component area of the model and the various subject areas that compose it.
XML (extensible markup language) is a system for defining, validating and sharing document formats. It is a simplified subset of the standard generalized markup language (SGML) with a few additional syntax rules. XML is a project of the World Wide Web Consortium (W3C, www.w3c.org) originally developed to make the Web a more useful resource. Its application is critical on the Web, but its domain now covers most aspects of IT. For our meta data purpose of modeling XML document structures, the actual use of XML is difficult to quantify because it is used for so many applications. XML documents are used in a variety of places and for many processes throughout the enterprise, including data transport between applications and specifying the utilization of Web services. The structure, use and role of these documents in the enterprise must be managed to prevent redundant efforts and the creation of incompatible systems. Management of the XML artifacts is a critical part of managing enterprise information systems. Thus, the complete meta data model must address XML uses.
This component of the complete meta model contains five subject areas. The XML schema and DTDs areas describe elements that may be used in XML documents that conform to that XML schema or DTD. The XML schema serves for both structuring documents and driving applications that interpret and parse XML documents. The XML transformations (XSLT) subject area is a transformation language in XML syntax that transforms other XML documents. This is a central piece of XML technology for data transfer and manipulation in the integration of systems. The business transactions subject area describes how electronic business processes function by exchanging data packages with other processes. The processes and their interactions can be specified by XML documents. The integration of external systems and internal systems can be done with this technology. The classification scheme subject area describes how a document classification scheme is like the searchable catalog of a library. With lots of XML documents and XML schemas, locating relevant documents can be very difficult. A classification scheme is needed to help manage this task. These subject areas overlap in varying degrees. XML schema is of central importance and is referenced by the other areas.
XML schemas define the structure of valid XML documents and drive applications by describing the elements and XML types that may be used in a document. The management of the use and reuse of XML schemas is critical because of their number and complexity. To help in the management of these schemas, the meta model tracks what has been defined as the life cycle of XML schemas and how they are used. An XML document is composed of elements and their content. The elements may have attributes, and the value of the element is the content. The mapping of data sources described in earlier portions of this series (see my June column) is based on treating different types of data sources as having a uniform top-level structure. The structures within that component were called DATA PACKAGE, DATA GROUP and DATA ELEMENT. To handle this type of structure in the XML schema model, we have the associations that an XML SCHEMA is a DATA PACKAGE, an XML ELEMENT DECLARATION and XML TYPE DEF are DATA GROUPs, and XML element attributes are DATA ELEMENTs. Subtyping on the needed XML parts accomplishes the needed correspondences. XML ELEMENT DECLARATION and XML TYPE DEF are subtypes of XML DATA GROUP, which is a subtype of DATA GROUP. XML ATTRIBUTE DEF and XML SIMPLE CONTENT are subtypes of XML DATA ELEMENT. This allows the uniform treatment of XML ELEMENT DECLARATIONS and XML TYPE DEFINITIONS as DATA GROUPs and the uniform treatment of XML ELEMENT ATTRIBUTEs and ELEMENT SIMPLE CONTENT as DATA ELEMENTs. The latter is required because the difference between attributes with values and the XML simple content value is nonexistent at a purely functional level for mapping information.
DTDs cannot define types and derived types such as XML schemas, which is needed for more advanced applications. DTDs provide entity definitions, a concept that XML schemas do not have.
While DTDs are not schemas, they are used like a schema. By making DTDs a subtype of schemas, the DTD gets the uniform treatment for mappings and dependencies, although they cannot be parsed like an XML document. XML SCHEMA is a subtype of XML DOC. The schema defines both the XML ELEMENT DECLARATION and XML TYPE DEFs. The definition of those XML ELEMENT DECLARATIONs and XML TYPE DEFs may be imported from another schema, which is handled by the IMPORT SCHEMA entity. The IMPORT SCHEMA is found via a URI LOCATOR. URI LOCATORs are handled as changeable references to XML DOCs. The link between an XML document and its possible defining schemas is made through the URI LOCATOR for the XML schema as the XML DOC TO SCHEMA LINK. The rest of the subject area deals with the real internal structure of an XML schema and the parts needed for mapping information.
XSLT, a W3C standard, is a transformation programming language in XML syntax that drives an XSLT processor to transform XML documents. The complete meta model handles the structural information of XSLT and the way in which it is integrated with the other processes. An XSLT document is an XML document as well as a subtype of TRANSFORMATION GROUP from the enterprise model component (see June column). This allows the modeling of its mapping nature and the modeling of how and when it is executed. An XSLT document can define a set of parameters that drives the XSLT. XSLT documents can also import other XSLT documents for reuse.
A business transaction is the exchange of one or more electronic documents, many XML, by two or more processes. A PROCESS is a set of specified INTERACTIONs that occur in a given TRANSITION pattern. INTERACTIONs are the centering concept of this area. The INTERACTIONs may be paired with an INTERACTION on another PROCESS. INTERACTIONs are performed by a SOFTWARE MODULE (see July column); they are part of a PROCESS, sequenced by TRANSITIONs, and send and receive documents. TRANSITIONs control the sequence of the INTERACTIONs. The TRANSITIONs entity indicates the successor INTERACTIONs of a source INTERACTION. The TRANSACTION CONTROL entity handles transaction integrity for the process' interaction transitions. A DOCUMENT ENVELOPE can have one or more BUSINESS DOCUMENTs as ATTACHMENTs and each attached BUSINES DOCUMENT may have its own security control in the DOCUMENT SECURITY entity. The documents can be of any form, not just XML. The MESSAGING CONTROL entity specifies the service and protocol if messaging is used by the INTERACTION. The security control specification can be contained in an XML document that can be located via a URI. The BUSINESS DOCUMENTs and the DOCUMENT ENVELOPE may be XML documents that are defined by an XML schema that is located via a URI. Finally, the PROCESS, because it may be specified as an XML file, may also be located via a URI. The WEB SERVICES BINDING entity indicates what INTERACTIONs are surfaced at a given URL with a given name. It also indicates which WSDL XML document, through a URI LOCATOR, is specifying this Web service.
A document classification scheme is like the searchable catalog of a library. Although document classification is not related to an XML standard, it plays a critical role in information management. Much of the information contained in XML documents, XML schema parts and business transaction parts needs to be classified if it is to be useful. Classification is necessary to reuse parts and locate relevant documents. This subject area provides links to XML documents and thus to XML SCHEMAs, XML NAMESPACEs and XML DATA GROUPs, which are XML ELEMENT DECLARATIONs and XML TYPE DEFs. CLASSIFICATION SCHEME is the top level for classification and may have many CLASSIFICATION LEVELs. CLASSIFICATION ITEM is the lowest level of a classification and is a child of the CLASSIFICATION LEVEL. The CLASSIFICATION LEVEL defines the levels and CLASSIFICATION ITEM defines the members of the level.
We now have a consolidated view of all components that compose the MME and the complete meta data model. Although many companies understand the importance of the MME, few have the experience to construct the underlying data models from scratch. This is where the complete meta data model can be used to get a head start on a project by providing a foundation that can be customized for the specific business needs of the enterprise.
Please view a PDF diagram of the XML, Messaging and Business Transactions component at http://www.dmreview.com/editorial/dmreview/200410/200410_jennings_1.pdf.
You may read Jennings' entire MME series at: http://www.dmreview.com/authors/author_sub.cfm?AuthorID=31122.
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