Basic XML Document Transfer

Basic transfer of XML documents refers to the transferring of an XML document from one point to another. For example, in the two previous chapters, which cover Oracle and SQL Server databases, an XML document was generated from an Oracle database. That XML document was then used to add an XML document into both the Oracle database and the SQL Server database, stored as XML data types. The stored XML document is now fully accessible by all XML capabilities that are available to both the Oracle and the SQL Server databases. The two previous chapters have already demonstrated a basic XML document transfer.

At the end of Chapter 6, a section describing XML Schema Definition (XSD) coding showed that a transformation could be applied to XML data. XML documents can be transferred as XML between two disparate platforms (in this case Oracle and SQL Server). However, one can even apply a transformation (a change) to the XML data at the source or target computers or even both the source and the target computers. So, XML data can be adapted by each of the two databases if you use something like XSD. The result is XML data conforming to both databases. Additionally, XSD can be used to apply a specific table structure to an XML document. Thus, not only is XML data transferred and transformed between two different platforms, it can even be transformed between two relational table structures. Obviously, there has to be common data content but the Oracle and SQL Server databases could actually contain two different sets of metadata. This is the power of XML.

Once again, the metadata is the data about the data. So, metadata consists of the tables, fields, and inter table relationships in each different database.

Basic XML document transfer between incompatible systems, such as two different databases, is really very primitive. In fact, the need to write custom code at either end of the transfer to convert between the two systems can be enormously time consuming. On the contrary, XML is actually an intelligent form of communication because XML contains both data and the semantics (the meaning) of that data. Continually mapping XML documents between two different points in a transfer, where those transfer points could be two completely different companies, can cause all sorts of problems. For example, even if two source and target companies dealt with similar types of data, their data structures could be completely different logically. And this is in addition to using different operating systems, different hardware platforms, or even database engines. There has to be a way to organize these data transfers so that they can be more universally understood and thus limit or completely remove the need for expensive and time-consuming custom coding.

The answer is sharing of XML data, not as just XML, but using software standards common to all platforms. The ideal result would be automated transfer of data between all kinds of computer systems without the need for any custom coding at either end. Part of this solution is realized by the inclusion of XML data types into relational databases. XML data types have been examined in both Oracle and SQL Server databases in the previous two chapters. The result is that XML documents can be stored at the end points of communication transfers, into a database, into a common format. That common format is the XML data type, which stores XML documents in their entirety. This includes all the bells and whistles such as the XML DOM. An XML document is universal in enforcement of its standardization.

Inclusion of XML data types into relational databases is a big piece of the puzzle along the path to the universal applicability of XML document communication transfers. Any type of computer system applies. How individual databases implement operations on an XML document once they are stored in a database, such as implementing SQL/XML standards, is localized to each database server. And this is also somewhat irrelevant to the topic of repetitive transfer of XML document data between two computers.

So whats next ?