Towards declarative XML querying

Extracting data from XML documents is an important issue for XML research and development. However, how XML documents are viewed determines how they can be queried. We first describe a natural way of viewing XML documents as in complex object data models so that we can easily comprehend XML data from a database point of view. We then illustrate how to use logical variables to extract data from XML documents. We also describe a rule-based declarative query language for XML. We demonstrate that our rule-based language provides a uniform framework that has the following advantages over other XML query languages including XQuery. First, it provides a natural way of separating querying and result constructing using the body and head respectively. Second, several rules can be used for the same query so that complex queries can be expressed in a simple and natural way. Also, its use of logical variables and rules makes many functions and operators in XQuery and XPath unnecessary or definable constructively. Finally, it provides natural and direct support for recursion as in deductive databases and has logical foundations that have played a significant role in database research in the past.