DTDs versus XML schema

Geert Jan Bex, Frank Neven, Jan Van den Bussche
2004 Proceedings of the 7th International Workshop on the Web and Databases colocated with ACM SIGMOD/PODS 2004 - WebDB '04  
Among the various proposals answering the shortcomings of Document Type Definitions (DTDs), XML Schema is the most widely used. Although DTDs and XML Schema Defintions (XSDs) differ syntactically, they are still quite related on an abstract level. Indeed, freed from all syntactic sugar, XML Schemas can be seen as an extension of DTDs with a restricted form of specialization. In the present paper, we inspect a number of DTDs and XSDs harvested from the web and try to answer the following
more » ... s: (1) which of the extra features/expressiveness of XML Schema not allowed by DTDs are effectively used in practice; and, (2) how sophisticated are the structural properties (i.e. the nature of regular expressions) of the two formalisms. It turns out that at present real-world XSDs only sparingly use the new features introduced by XML Schema: on a structural level the vast majority of them can already be defined by DTDs. Further, we introduce a class of simple regular expressions and obtain that a surprisingly high fraction of the content models belong to this class. The latter result sheds light on the justification of simplifying assumptions that sometimes have to be made in XML research.
doi:10.1145/1017074.1017095 dblp:conf/webdb/BexNB04 fatcat:5ceckj5e2fet3dhe2s4flyucty