XML for Data Exchange

The need to generate XML data from a variety of data sources is becoming increasingly important to a wide variety of data processing environments. Interoperability and data exchange between mainframe systems and other systems running on a variety of hardware and software platforms is essential.

XML—EXtensible Markup Language—is a way to generically describe data to facilitate interchange of data between applications. Our support for XML output is important for organizations that have the need to exchange mainframe data with applications/products running on different platforms or written in different languages.

With UltraQuest Reporter, users can generate output as XML documents. Within Reporter, the user can choose the new output type of XML and then generate the XML output based on the CREATE XML command of NOMAD version 7.50. By default, UltraQuest Reporter will generate hierarchical XML output for importing into those products or applications that understand one-to-many relationships. Simple or flat XML documents can also be created for SQL, row-oriented DBMS products such as SQL Server or Oracle.

An XML Schema can also be generated for those products that require more information about the structure and content of the XML data file being imported. The older version of the XML structured definition file or DTD (Document Type Definition) can be generated but will be included as part of the XML data file itself.

With UltraQuest Applications, developers can use the CREATE XML command to generate the types of XML documents discussed above.

The CREATE XML feature allows creation of valid XML documents in XML formats specified by the developer using mainframe data described by a 4GL schema. The XML output can be retained on the mainframe or transmitted to other platforms, where it can be used directly by a client process or transformed to a format usable by other systems. CREATE XML produces well-defined, self-contained, and understandable XML output that can be used by Java, Visual Basic, and other XML-enabled processes.

CREATE XML is a robust facility that combines XML support with the powerful data retrieval and data manipulation capabilities of the CREATE command. It is a marriage of full support of XML with CREATE functionality.

	CREATE XML benefits from existing capabilities: It allows generation of XML output using data sources described by 4GL schemas, and lets the user easily reference data from multiple data sources through a single schema. It leverages the full functionality of the CREATE command to retrieve, sort, summarize, join, and manipulate data. It lets the user define dynamic calculations (virtual columns) based upon database data. It translates hierarchical and relational data into the specified format, in this case, XML. It takes advantage of the CREATE command's ability to dynamically generate hierarchical XML documents (output).   Additional features specific to XML are provided with CREATE XML: A wide range of XML structures, such as elements, attributes, tag names, XML Schema, and DTD can be generated. XML attributes, like tag names, can be permanently defined for a given database or can be dynamically defined as needed for various XML applications. CREATE infers a default XML structure based upon the context of the request with tags that can be easily overridden by the user. Data collected by the 4GL is mapped into an XML hierarchical document structure. Complex XML element types can easily be represented within a CREATE request. CREATE’s default behavior can be overridden through system variables designed for XML use.

Generating XML data can be as simple as adding the XML keyword to an existing CREATE request. In cases where XML data must be produced to meet specific application needs, CREATE XML allows generation of a variety of complex XML structures.

Let’s look at this simple example of a CREATE XML request, which generates total income for each video store:

	create xml by storename sum(income);

This is the XML document file that is generated:

	<?xml version="1.0"?> <root> <node> <storeName>VIDEOHEAVEN</storeName> <incomeAmount>119152.63</incomeAmount> </node> <node> <storeName>VIDEO MADNESS</storeName> <incomeAmount>50300.24</incomeAmount> </node> <node> <storeName>VIDEO MAGIC</storeName> <incomeAmount>725580.55</incomeAmount> </node> </root>

The file includes default XML tags, like <node>, that indicate data structure, as well as custom XML tags, like <StoreName>, provided through the database metadata (schema).

Flat and Hierarchical XML

Generally, the CREATE XML command produces XML documents structured in one of two ways—flat and hierarchical. The following sections show simple examples of each type of document. The following examples show some simple XML document files produced by CREATE to show the difference between flat and hierarchical XML data.In some cases, an XML document may be a combination of hierarchical and flat structures.

A Flat XML Document

A flat XML document is very simplistic and is comparable to an external flat file, such as a QSAM file. It has a very simple XML structure. <row> tags enclose each data record. A flat XML document is geared for data import into products like spreadsheets or SQL tables, which do not have hierarchical structure. Flat XML documents are generic and suitable for use in a variety of products without the need to provide specific metadata to accompany the file.

This is an example of a flat XML document generated by CREATE XML. It shows video stores by state locations New Jersey and New York. Notice how the state value NY is repeated for each store within New York:

	<?xml version="1.0"?> <root> <row> <state>NJ</state> <storeName>VideoHeaven</storeName> </row> <row> <state>NY</state> <storeName>VideoMagic</storeName> </row> <row> <state>NY</state> <storeName>Video Madness</storeName> </row> <row> <state>NY</state> <storeName>Video Rentals</storeName> </row> </root>

A Hierarchical XML Document

By default CREATE XML produces a hierarchical XML document file. The intent of hierarchical XML is to preserve the data relationships produced by the CREATE request. A sort key represents a parent value, and the objects being sorted represent children of the parent key. A <node> tag indicates a break in the hierarchical structure. <node> tags are generated for sort breaks caused by BY items (sort keys) used in the request. Each set of records within a sort break is enclosed by an opening <node> tag and a closing </node> tag. Also, immediately after each sort value, <node> tags enclose each separate child record associated that sort value.

This is an example of a hierarchical XML document generated by CREATE XML. As in the flat example above, it shows video stores by state locations New Jersey and New York. In contrast to flat XML, sort values for the key State are not repeated for each store. The state value NY appears once for all stores within New York, and the <state> element is the parent of the <storeName> elements:

	<?xml version="1.0"?> <root> <node> <state>NJ</state> <node> <storeName>Video Heaven</storeName> </node> </node> <node> <state>NY</state> <node> <storeName>Video Magic</storeName> </node> <node> <storeName>VideoMadness</storeName> </node> <node> <storeName>VideoRentals</storeName> </node> </node> </root>

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