On 16.01.25 08:21, Jim Jones wrote: > On 16.01.25 07:11, Pavel Stehule wrote: >> It is better. > v2 attached updates the documentation. >> My note was related to a very different description of this >> functionality in DB2. So if you propose this function for better >> compatibility (and this function is implemented only by db2), it is >> surprising to see that this functionality is described (and probably >> implemented) very differently. Because I do not have db2 and I miss >> db2 knowledge, I don't know if differences in implementation and >> description are based on different technology (XML like graph or XML >> like string) or if it is something that is missing in this patch. > I suppose it's mostly because PostgreSQL and DB2 have different > structures for the XML data type; DB2 stores it in its native > hierarchical format rather than as text. > > Thanks for the review. > > Best, Jim
The DB2 "Document node constructors" might provide some insights into its behavior regarding well-formed XML documents [1]: "No validation is performed on the constructed document node. The XQuery document node constructor does not enforce the XML 1.0 rules that govern the structure of an XML document. For example, a document node is not required to have exactly one child that is an element node." This suggests that DB2's design reflects a different approach to handling XML, focusing less on enforcing XML 1.0 constraints. It appears to be more of a design philosophy regarding how XML is integrated into the database system as a whole, rather than just a difference in the implementation of the XMLDocument function. PostgreSQL does not support the RETURNING SEQUENCE or RETURNING CONTENT clauses explicitly. Instead, it implicitly uses RETURNING CONTENT[2] in functions that require it. Since RETURNING CONTENT implies that the output is a well-formed XML document (e.g., single-rooted), I would argue that the behavior of this patch is more intuitive and aligns best with the expectations of XML document structure. Any thoughts? Best, Jim 1 - https://www.ibm.com/docs/en/db2/11.1?topic=constructors-document-node 2 - https://www.postgresql.org/docs/17/xml-limits-conformance.html
