I have added a modified version of this to the SGML documentation, under data types.
--------------------------------------------------------------------------- bruce wrote: > Here is an new XML section for our SGML documentation. It explains the > various XML capabilities, if we support them, and how to use them. > > Comments? > > --------------------------------------------------------------------------- > > > XML Document Support > ==================== > XML support is not one capability, but a variety of features supported > by a database. These capabilities include storage, import/export, > validation, indexing, efficiency of modification, searching, > transformating, and XML to SQL mapping. PostgreSQL supports some but > not all of these XML capabilities. Future releases of PostgreSQL will > continue to improve XML support. > > Storage > ------- > PostgreSQL stores XML documents as ordinary text documents. It does not > split apart XML documents into its component parts and store each > element separately. You can use middle-ware solutions to do that, but > once done, the data becomes relational and has to be processed > accordingly. > > Import/Export > ------------- > Because XML documents are stored as normal text documents, they can be > imported/exported with little complexity. A simple TEXT field can hold > up to 1 gigabyte of text, and large objects are available for larger > documents. > > Validation > ---------- > /contrib/xml2 has a function called xml_valid() that can be used in > a CHECK constraint to enforce that a field contains valid XML. It > does not support validation against a specific XML schema. A > server-side language with XML capabilities could be used to do > schema-specific XML checks. > > Indexing > -------- > Because XML documents are stored as text, full-text indexing tool > /contrib/tsearch2 can be used to index XML documents. Of course, the > searches are text searches, with no XML awareness, but tsearch2 can be > used with other XML capabilities to dramatically reduce the amount of > data processed at the XML level. > > Modification > ------------ > If an UPDATE does not modify an XML field, the XML data is shared > between the old and new rows. However, if the UPDATE modifies a XML > field, a full modified copy of the XML field must be created internally. > > Searching > --------- > XPath searches are implemented using /contrib/xml2. It processes XML > text documents and returns results based on the requested query. > > Transforming > ------------ > /contrib/xml2 supports XSL transformations. > > XML to SQL Mapping > ------------------- > This involves converting XML data to and from relational structures. > PostgreSQL has no internal support for such mapping, and relies on > external tools to do such conversions. > > Missing Features > ---------------- > o XQuery > o SQL/XML syntax (ISO/IEC 9075-14) > o XML data type optimized for XML storage > > See also http://www.rpbourret.com/xml/XMLAndDatabases.htm > > -- > Bruce Momjian [EMAIL PROTECTED] > EnterpriseDB http://www.enterprisedb.com > > + If your life is a hard drive, Christ can be your backup. + -- Bruce Momjian [EMAIL PROTECTED] EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
