On XML integrity constraints in the presence of DTDs

Abstract

The article investigates XML document specifications with DTDs and integrity constraints, such as keys and foreign keys. We study the consistency problem of checking whether a given specification is meaningful: that is, whether there exists an XML document that both conforms to the DTD and satisfies the constraints. We show that DTDs interact with constraints in a highly intricate way and as a result, the consistency problem in general is undecidable. When it comes to unary keys and foreign keys, the consistency problem is shown to be NP-complete. This is done by coding DTDs and integrity constraints with linear constraints on the integers. We consider the variations of the problem (by both restricting and enlarging the class of constraints), and identify a number of tractable cases, as well as a number of additional NP-complete ones. By incorporating negations of constraints, we establish complexity bounds on the implication problem, which is shown to be coNP-complete for unary keys and foreign keys.

On Reasoning about Structural Equality in XML: A Description Logic Approach

“…In particular, constraints that resemble a form of keys and functional constraints have been considered in [2,3,8,17]. However, there still remains the problem of reasoning about arbitrary structural equality between (sub)documents with unstructured components.…”

Types and Constraints: From Relational to XML Data

“…Although XML schemas allow to specify keys or references in terms of Xpath [18], such style of specification is rather intricate especially when it comes to reasoning about constraints. Indeed, constraints for semi-structured data and XML [38,39], keys and foreign keys for XML [26,27] have received a lot of attention from the database community. Update anomalies and normal forms for XML documents have been investigated in [14].…”

Consistency management with repair actions

“…Repair actions that make a document consistent with respect to some xlinkit constraint, but at the same time violate the document's grammar should not be permitted -the grammar of a document is a lower-level mechanism and takes precedence. It is not possible to statically compare our constraints against a DTD or Schema to predict whether this behaviour must necessarily occur [7], but it should be possible to incrementally revalidate a document after executing each action and to retract the action if it violates the grammar.…”