Now that the xml type as per SQL:2003 is pretty much finished, one starts to wonder about what useful things one might do with it. What we have so far contains only functions to construct XML values from SQL data, but there is nothing that you can do with the type at the moment except look at it.
The basic kind of operation on XML values is XPath queries. This is the equivalent of what substring/position/length/concat/etc. does for text types, and it's also the gist of the contrib/xml2 module, and it's typically provided by other DBMS with "XML support". SQL:2003 says nothing on the matter, whereas SQL:2006 specifies XQuery support, but I don't think we can implement that at the moment because there is no library available to do it. (XPath is in libxml2.) So, while I realize that I've been arguing for a lean core recently, I want to propose that we add a small set of XPath support functions to the core. This would come down to approximately the following set xpath_boolean(query, xml) xpath_number(query, xml) xpath_string(query, xml) xpath_nodeset(query, xml) -- API and return type still unclear We also have prospects that later on we might get fancy GIN-based indexing support for XPath, which might need another xpath_matches() function or operator of some kind. As far as contrib/xml2 is concerned, I'm not going to make any efforts to make the interface compatible because that module has a rather pragmatic design, whereas I'd rather just provide the raw operations that can be assembled easily by the user to achieve some of the things that contrib/xml2 does now. Once some description of transition steps has been developed, I'd deprecate the contrib/xml2 module and probably remove it after 8.3. In the wiki we have collected some random ideas of other interesting operations on XML types (http://developer.postgresql.org/index.php/XML_Todo, near the bottom). That list at the moment says: DTD validation Relax-NG XSLT XML Canonical (to compare XML values) Pretty-printing XML (e.g., indenting) I would argue for keeping these sort of things in a non-core module or a PgFoundry repository. Comments? -- Peter Eisentraut http://developer.postgresql.org/~petere/ ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
