Schemas are important validation tools which can ensure data is valid and well formed for use. There are different varieties that can be used to verify a document and ensure conformance to standards. Some use a tree hierarchy and others just simple constructs. Lee and Chu (2000) note the following in their paper; DTD, XSD, SOX, Schematron and DSD. Fawcett et al (2012) mention Schematron, DTD, RELAX NG, and XSD. I will discuss some of these in comparison to DTD and XSD which are follow-ons from this week’s Schema discussions.
This Schema type on uses attributes and elements and follows a hierarchy in structure type. It is very simplistic and uses few attribute definitions, and does not follow XML type syntax. However, despite its simplistic nature, it is the most widely used standard according to Lee and Chu (2000).
The true XML Schema Definition is very different from DTD in that it can be very granular in its descriptive elements and ...view middle of the document...
(2012) as well as the need to deal with identification of data in the document help prior to run-time. Although not a widely used as XSD it seems easier to implement and understand, while still improving some of the failings in the DTD model.
Where the previous types of validation used a strict comparison model, the Schematron model uses an appearance directive which is closer in comparison to HTML structuring (Fawcett et al. 2012). Furthermore Schematron allows the author to define quantity, configuration and nature of document rules. However this method is reliant on XSLT to transform the syntax form the document and the rule set and compare them for conformance. This allows for a strong focus on constraints. (Lee and Chu, 2000)
Mentioned lightly by Lee and Chu (2000) this method follows a DTD format with emphasis on an object oriented way. This allows for an extension of the DTD model to include inheritance of elements and increasing the amount of available data types. (Lee and Chu, 2000)
As a model focusing on constraints of elements, this model more closely resembles the Schematron methodology. It uses context dependant descriptions and is akin to XSLT in expressive power, according to Lee and Chu (2000).
These validation models are similar in some of their functionality, but vastly different in either improvement on previous technologies or method of delivery. DTD, SOX are simpler methods of non XML type syntax, in contrast XSD, DSD, RELAX NG and Schematron use XML or XSLT translational elements for setting rules. Schematron seems the least restrictive in directives, where SOX would seem the most restrictive because of the object oriented methodologies. Either choice will allow for the presentation of data that should present in a more compatible manner for other applications use.
Fawcett, J., Quin, L.R.E. & Ayers, D., 2012. Beginning XML. 5th ed. Indianapolis, IN: John Wiley & Sons, Inc.
Lee, D. & Chu, W.W., 2000. Comparative Analysis os Six XML Schema Languages. ACM SIGMOD Record, 29(3), pp.76-87.