A Three-Layered XML View Model: A Practical Approach Rajugan, R. 1 , Elizabeth Chang 2 , Tharam S. Dillon 1 , and Ling Feng 3 1 eXel Lab, Faculty of IT, University of Technology, Sydney, Australia {rajugan, tharam}@it.uts.edu.au 2 School of Information Systems, Curtin University of Technology, Australia Elizabeth.Chang@cbs.cutin.edu.au 3 Faculty of Computer Science, University of Twente, The Netherlands ling@ewi.utwente.nl Abstract. Since the early software models, abstraction and conceptual seman- tics have proven their importance in software engineering methodologies. For example, Object-Oriented conceptual modeling offers the power in describing and modeling real-world data semantics and their inter-relationships in a form that is precise and comprehensible to users. Conversely, XML is becoming the dominant standard for storing, describing and interchanging data among various Enterprises Information Systems and databases. With the increased reliance on such self-describing, schema-based, semi-structured data language/(s), there ex- ists a requirement to model, design, and manipulate XML data and associated semantics at a higher level of abstraction than at the instance level. But, exist- ing Object-Oriented conceptual modeling languages provide insufficient mod- eling constructs for utilizing XML schema like data descriptions and con- straints, and most semi-structured schema languages lack the ability to provide higher levels of abstraction (such as conceptual models) that are easily under- stood by humans. To this end, it is interesting to investigate conceptual and schema formalisms as a means of providing higher level semantics in the con- text of XML-related data engineering. In this paper, we use XML view as a case in point and present a three-layered view model with illustrated examples taken from a real-world application domain. We focus on conceptual and schema view definitions, view constraints, and the conceptual query operators. 1 Introduction In software engineering, many methodologies have been proposed to capture real- world problems into manageable segments, which can be communicated, modeled, and developed into robust maintainable software systems. Since the early software models, abstraction and conceptual semantics have proven their importance in soft- ware engineering methodologies. For example, in Object-Oriented (OO) conceptual models, they have the power in describing and modeling real-world data semantics and their inter-relationships in a form that is precise and comprehensible to users [17, 23]. With the emergence of semi-structured data, Semantic Web (SW) [44], web services [46], and ubiquitous systems, it is important to investigate new data models