The document, XMLConProp.pdf, presents a model and XML encoding that helps bridge the flexibility gap currently experienced between XML Schema and RDF Schema users. The section below describes the overall approach and goals for the work. Please refer to the document for details. We've also provided xmlInstanceHierarchy.pdf document that presents some very early work, referenced by the XMLConProp.pdf document.
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What are Constrained Properties?
Modeling information as a set of properties, defined on demand, that then may have values restricted by constraints is a well known technique used throughout the information and computer science communities. For example, well back in early 1980s, researchers were using such notions when describing conceptual models for copiers as part of their Trillium project [6] for investigating methods to enable dynamic user interfaces that could better expose the capabilities of those copiers.
Our proposed variant of the model focuses on five core building blocks:
· Flexible definitions for classes of properties
· Support for use-oriented membership of properties within those classes
· Suggestion-based typing of values for those properties in use, including the ability to create potential options for those values (think code lists)
· Powerful expressiveness for defining constraints on the values of a given property and for values amongst properties
· Late binding for both property definitions and suggested value types
While dynamic binding of both types and values can cause headaches for those embarking on trying to define structure and format for computer consumption, an encoding for the conceptual model can address some of the vagueness and ambiguity through the introduction of a framework that helps connect the various pieces. Such a framework is a core part of our effort in that it is an essential part for supporting XML-enabled validation.
An Example
Business Entity: Consider a service offered by the USPS that delivers packages in 3 days within the contiguous 48 states and within 5 days for all other national deliveries, provided the package size is limited to a length and girth of 108 inches and a weight of 70 lbs. To specify this service, its description needs to specify what packages are acceptable and differentiate the two potential service times.
ConceptualModel: In one representation, two types of property classes would be defined: one for describing the physical properties for the package and another that includes properties about the delivery for the package. The former would include the properties "Length," "Girth" and "Weight" while the latter would include "DeliveryTime" and "DeliveryScope." Suggested value types for the physical properties would be a distance measurement, a distance measurement, and a weight measurement, respectively. Suggested types the package delivery properties would be a time duration and a set of codes including, e.g., "WithinContigousStates" and "BeyondContiguousStates." Constraints would be placed on "Length," "Girth," and "Weight" limiting values to less than 108 in, 108 in, and 70 lb, respectively. In addition, a pair of constraints would be defined for "DeliveryScope" indicating that if the value is set to "WithinContigousStates," then the value of the "DeliveryTime" would be 3 days. If it is set to "BeyondContiguousStates," then the value would be 5 days.
