Managing large quantities of structured and unstructured data is a primary function of information systems. The concept of “Neutrality of Data” was described already. A “Data Model” is the concept of data being made “basically available” – in the sense of being stored – in a data “base“:
- In software engineering a data model is an abstract model on how data is stored and accessed. It explicitly determines the structure of data for storage.
- The main aim of data models is to support the development of information systems [by providing the definition and format of the data].
- Designing a data model is the complex task of software engineers.
The design of a data model has several challenges:
- Business rules specific the work flow in a particular place or organisation and are often fixed in the structure of a data model. Small changes in the way business is conducted lead to large changes in the data model, computer systems and interfaces.
- Entity types not identified or incorrectly identified lead to duplication of data and therefore additional costs for system development and maintenance.
- Data models for different systems are arbitrarily different, resulting in complex interfaces needed to enable the sharing of data. Data structure and meaning of data has to been standardised for electronic and automatic data sharing.
XML as “glue” for interfacing systems
The problems in data modelling or design are due to a lack of standards that will ensure that data models will both meet business/organisational needs/rules and consistency. This is one of the reasons the W3C developed the Extensible Markup Language (XML):
Extensible Markup Language (XML) is the “glue” for interfacing systems.
- XML is a set of rules for encoding documents in machine-readable form.
- XML contains business rules.
- Each single data item in a data base is in detail described in an XML schema. XML schema acts as data model for automated storage and retrieval of the information.
- The concept of XML Registry and Namespaces enables the interaction of the XML schemas in federated systems and their data bases.
XML can describe the business processes defined in human readable work flow diagrams for information exchange. The XML schema acts as data model for storage, retrieval and definition of the data. No further data model or matrix is required, but for interoperability reasons the W3C advised the use of XML Registry and the concept of Namespaces.
by Joachim Beckh
 Ergo sum: If a concept excludes or avoids the system development approach, no data model is needed (à XML Schema).
 Citation: “… if this is done consistently across systems then compatibility of data can be achieved. If the same data structures are used to store and access data then different applications can share data. The results of this are indicated above. However, systems and interfaces often cost more than they should, to build, operate, and maintain. They may also constrain the business rather than support it. A major cause is that the quality of the data models implemented in systems and interfaces is poor“. by West and Fowler (1999)
 Business rules describe the operations, definitions and constraints that apply to an organization, they can apply to people, processes, corporate behaviour and computing systems. The common approaches to visualize Business Rules are flow charts, to define them for electronic exchange XML.