The quality of the XML Web

We collect evidence to answer the following question: Is the quality of the XML documents found on the Web sufficient to apply XML technology like XQuery, XPath and XSLT? XML collections from the Web have been previously studied statistically, but no detailed information about the quality of the XML documents on the Web is available to date. We address this shortcoming in this study. We gathered 180K XML documents from the Web. Their quality is surprisingly good; 85.4% are well-formed and 99.5% of all specified encodings is correct. Validity needs serious attention. Only 25% of all files contain a reference to a DTD or XSD, of which just one-third are actually valid. Well-formedness errors and validity errors are studied in detail. Our study is well-documented, easily repeatable and all data is publicly available [21], (Grijzenhout, 2010) [52]. This paves the way for a periodic quality assessment of the XML Web.