XML Input Format Fields

The structure of the input records generated by the XML input format is determined at run time, depending on the document being parsed, and on the values specified for the input format parameters.

The XML input format parses an XML document by "visiting" the nodes in the document, and the input record fields are the attributes and values of the nodes that are visited by the XML input format.

By default, nodes are visited from the document root, that is, the single top-level node in an XML document that contains all the other nodes in the document.
However, by supplying an XPath in either the from-entity or as a value of the rootXPath parameter, users can specify that the document nodes are to be visited starting from the node(s) selected by the XPath.

Before parsing the XML document and return the input records, the XML input format initially examines the nodes found along the paths from the root node or from the node(s) selected by the user-supplied root XPath to the first n leaf nodes, where n is the value of the dtNodes parameter.
During this phase, the XML input format creates a representation of the tree structure ("schema" tree) by merging nodes with the same name and hierarchical position. When completed, the schema tree contains one single instance of each node type, and each node contains an attribute set equal to the union of all the attributes found in the nodes of that type.
At this moment, an input record field is created for each attribute belonging to a node type and for each node type having a value.

Once the schema tree has been determined and the input record structure has been created, the XML input format parses the XML document and generates input records, visiting the document nodes and extracting their values and attributes.
The XML input format implements three different algorithms to decide how document nodes will be visited. The three algorithms represent three different ways in which the information contained in an XML document can be retrieved, and the choice of an algorithm depends on the structure of the document and on the structure of the information that needs to be extracted.
Since different algorithms visit different sets of nodes, the choice of an algorithm affects which fields (i.e. which node attributes and values) will be contained in the input records.
Users can specify the algorithm to use through the fMode ("field mode") parameter, which can be set to "Branch", "Tree", or "Node".

Branch Field Mode

This mode is appropriate for documents in which each hierarchical level consists of nodes of the same type, as depicted in the following diagram:

In this structure, the root node contains only nodes of type "A", and each "A" node contains only nodes of type "B".
For example, the root of the following XML document contains "Continent" nodes only; each "Continent" node contains "Country" nodes only, and each "Country" node contains "City" nodes only:

<?xml version="1.0" ?> 
<World> 

  <Continent ContinentName='North America'> 

	<Country CountryName='USA'> 
	<City> Redmond </City> 
	<City> San Francisco </City> 
	</Country> 

	<Country CountryName='Canada'> 
	<City> Vancouver </City> 
	<City> Toronto </City> 
	</Country> 

  </Continent> 

  <Continent ContinentName='Europe'> 

	<Country CountryName='Italia'> 
	<City Population='3350000'> Roma </City> 
	<City> Milano </City> 
	</Country> 

  </Continent> 

</World> 

The schema tree extracted from this example document specifies that the document root node contains nodes of the "Continent" type, and that nodes of this type have a "ContinentName" attribute. "Continent" nodes, in turn, contain nodes of the "Country" type, with a "CountryName" attribute; finally, "Country" nodes contain nodes of the "City" type, and nodes of this type have a value, and a "Population" attribute.
The input records generated after the schema tree would thus contain four fields: "ContinentName", "CountryName", "City", and "Population".

When using the "Branch" field mode, the XML input format generates an input record for each path from the document root node or from the node(s) selected by the user-supplied root XPath to all the leaf nodes. Each input record contains the attributes and values of the nodes encountered along the path:

Record 1	Record 2
Record 3	Record 4
Record 5

ContinentName CountryName City		Population
------------- ----------- ------------- ----------
North America USA		 Redmond	 -
North America USA		 San Francisco -
North America Canada	Vancouver	 -
North America Canada	Toronto	 -
Europe		Italia	Roma		3350000
Europe		Italia	Milano		-

Tree Field Mode

This mode is appropriate for documents in which a specific hierarchical level contains child nodes all having different types, as depicted in the following diagram:

In this structure, the root node contains only nodes of type "A"; each "A" node however contains nodes all having different types (a single "B" node, a single "C" node, and a single "D" node).
For example, the root of the following XML document contains "Message" nodes; each "Message" node contains a single "From" node, a single "To" node, and a single "Body" node:

<?xml version="1.0" ?> 
<Messages>

  <Message Date='2004-05-28T12:24:05'>
	<From> Gabriele </From>
	<To> Monica </To>
	<Body> How's going? </Body>
  </Message>

  <Message Date='2004-05-28T13:01:14'>
	<From> Monica </From>
	<To> Gabriele </To>
	<Body> Fine, thanks. </Body>
  </Message>

</Messages>

The schema tree extracted from this example document specifies that the document root node contains nodes of the "Message" type, and that nodes of this type have a "Date" attribute. "Message" nodes, in turn, contain nodes of the "From", "To", and "Body" types, each type having a node value.
The input records generated after the schema tree would thus contain four fields: "Date", "From", "To", and "Body".

When using the "Tree" field mode, the XML input format generates an input record for each subtree that includes all nodes of distinct types. Each input record contains the attributes and values of the nodes found in the subtrees, together with the attributes and values of the nodes encountered along the paths from the document root node or from the node(s) selected by the user-supplied root XPath to the subtree root nodes:

Record 1

Record 2

Date				From	 To	 Body
------------------- -------- -------- -------------
2004-05-28 12:24:05 Gabriele Monica   How's going?
2004-05-28 13:01:14 Monica   Gabriele Fine, thanks.

While parsing an XML document in "Tree" mode, if a subtree is found containing multiple instances of the same node type, that subtree is "replicated" combinatorially to generate all the possible subtrees containing one single instance of each node type.
The following diagram depicts an XML document in which a subtree contains multiple instances of the same node type:

In this diagram, the "A" node contains one instance of the "B" node type, two instances of the "C" node type, and two instances of the "D" note type.
For example, the "Message" node in the following XML document contains a single "From" node, two "To" nodes, and two "Body" nodes:

<?xml version="1.0" ?> 
<Messages>

  <Message Date='2004-05-28T12:24:05'>
	<From> Gabriele </From>
	<To> Jeff </To>
	<To> Steve </To>
	<Body Language='ENU'> Review ready? </Body>
	<Body Language='ITA'> E' pronta la review? </Body>
  </Message>

</Messages>

• From "Gabriele" to "Jeff" in the "ENU" language;
• From "Gabriele" to "Jeff" in the "ITA" language;
• From "Gabriele" to "Steve" in the "ENU" language;
• From "Gabriele" to "Steve" in the "ITA" language;

When using the "Tree" field mode, these "Message" subtrees are replicated combinatorially to generate all the possible subtrees containing one single instance of each of the "From", "To", and "Body" node types:

Record 1	Record 2
Record 3	Record 4

Date				From	 To	Body				 Language
------------------- -------- ----- -------------------- --------
2004-05-28 12:24:05 Gabriele Jeff  Review ready?		ENU
2004-05-28 12:24:05 Gabriele Jeff  E' pronta la review? ITA
2004-05-28 12:24:05 Gabriele Steve Review ready?		ENU
2004-05-28 12:24:05 Gabriele Steve E' pronta la review? ITA

Node Field Mode

This mode is appropriate for situations in which the information to be retrieved is associated with a specific node type only.
For example, the relevant information in the document depicted by the following diagram might be associated with "B" node types only:

When using the "Node" field mode, the XML input format generates an input record for each root node, either the document root or the node(s) selected by the user-supplied root XPath. Each input record contains the attributes and values of that node only:

Record 1

Record 2

CountryName
-----------
USA
Canada
Italia

Field Types

• If all the non-empty field values (node values or attribute values) encountered while constructing the schema tree are formatted as decimal numbers, then the field is assumed to be of the REAL type.
• If all the non-empty field values (node values or attribute values) encountered while constructing the schema tree are formatted as integer numbers, then the field is assumed to be of the INTEGER type.
• If all the non-empty field values (node values or attribute values) encountered while constructing the schema tree are formatted as timestamps in the format specified by the iTsFormat parameter, then the field is assumed to be of the TIMESTAMP type.
• Otherwise, the field is assumed to be of the STRING type.

As an example, the following help command displays the input record structure determined by the XML input format when parsing the previous "Cities" example XML document:

C:\>LogParser -h -i:XML Cities.xml

Fields:

  ContinentName (S)	 CountryName (S)	 City (S)	 Population (I)

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