XMLReader

Short Description

XMLReader reads data from XML files using DOM technology. It can also read data from compressed files, input port, and dictionary.

Which XML Component?

Generally, use XMLExtract. It is fast and has GUI to map elements to records. It is based on SAX. XMLReader can use more complex XPath expressions than XMLExtract, e.g. it allows you to reference siblings. On the other hand, this XMLReader is slower and needs more memory than XMLExtract. XMLReader is based on DOM. XMLReader supersedes the original XMLXPathReader. XMLXPathReader can use more complex XPath expressions than XMLExtract. XMLXPathReader uses DOM.

COMPONENT	DATA SOURCE	INPUT PORTS	OUTPUT PORTS	EACH TO ALL INPUTS	DIFFERENT TO DIFFERENT OUTPUTS	TRANSFORMATION	TRANSF. REQ.	JAVA	CTL	AUTO-PROPAGATED METADATA
XMLReader	XML file	0-1	1-n	x	✓	x	x	x	x	x

XMLReader, XMLExtract and XMLXPathReader send data to ports as defined in their Mapping or Mapping URL attribute.

Ports

PORT TYPE	NUMBER	REQUIRED	DESCRIPTION	METADATA
Input	0	x	For port reading. See Reading from Input Port in Supported File URL Formats for Readers.	One field (byte, cbyte, string).
Output	0 ... n-1	✓	For correct data records. Connect more than one output ports if your mapping requires that.	Any
	1-n	x	Error port	Restricted format. See Metadata here below.

Metadata

Metadata Propagation

XMLReader does not propagate metadata.

Metadata Templates

XMLReader has metadata templates on the error port. There are two templates: XMLReader_TreeReader_ErrPortWithoutFile and XMLReader_TreeReader_ErrPortWithFile.

FIELD NUMBER	FIELD NAME	DATA TYPE	DESCRIPTION
0	port	integer	The number of the output port where errors occurred.
1	recordNumber	integer	Record number (per source and port).
2	fieldNumber	integer	Field number
3	fieldName	string	Field name
4	value	string	The value which caused the error
5	message	string	Error message
6	file	string	Source name. This field is optional

Requirements on Metadata

Input metadata has one field with datatype byte, cbyte or string. The metadata on each of the output ports does not need to be the same. Each of these metadata can use Autofilling Functions. If you intend to use the last output port for error logging, metadata must have a fixed format. Field names can be arbitrary, field types must be same as from the template.

XMLReader Attributes

ATTRIBUTE	REQ.	DESCRIPTION	POSSIBLE VALUES
Basic
File URL	Yes	Specifies which data source(s) will be read (XML file, input port, dictionary). See Supported File URL Formats for Readers.
Charset		Encoding of records that are read. When reading from files, the charset is detected automatically (unless you specify it yourself). Important: if you are reading from a port or dictionary, always set Charset explicitly (otherwise errors will occur). There is no autodetection as in reading from files.	ISO-8859-1 (default) |
Data Policy		Determines what should be done when an error occurs. For more information, see Data Policy.	Strict (default) | Controlled | Lenient
Mapping	[1]	The mapping of the input XML structure to output ports. For more information, see Defining the Mapping below.
Mapping URL	[1]	An external text file containing the mapping definition. For more information, see Defining the Mapping below.
Implicit mapping		If true, map element values to the fields having a same name in record. Example: An element (salary) is automatically mapped onto field of the same name (salary).	If true, map element values to the fields having a same name in record. Example: An element (salary) is automatically mapped onto field of the same name (salary).
Advanced
XML features		A sequence of individual true/false expressions related to XML features which should be validated. The expressions are separated from each other by a semicolon. For more information, see XML Features.

[1] One of these must be specified. If both are specified, Mapping URL has higher priority.

Details

Records and fields to be send out to the output ports are specified using XML elements and attributes. Each Context element corresponds to one output port attached. Each Mapping element defines a mapping to one field. See the example below.

Example 21. Mapping in XMLReader

<Context xpath="/employees/employee" outPort="0">
    <Mapping nodeName="salary" cloverField="basic_salary"/>
    <Mapping xpath="name/firstname" cloverField="firstname"/>
    <Mapping xpath="name/surname" cloverField="surname"/>
    <Context xpath="child" outPort="1" parentKey="empID" generatedKey="parentID"/>
    <Context xpath="benefits" outPort="2" parentKey="empID;jobID" generatedKey="empID;jobID"
            sequenceField="seqKey" sequenceId="Sequence0">
        <Context xpath="financial" outPort="3" parentKey="seqKey" generatedKey="seqKey"/>
    </Context>
    <Context xpath="project" outPort="4" parentKey="empID;jobID" generatedKey="empID;jobID">
        <Context xpath="customer" outPort="5" parentKey="projName;projManager;inProjectID;Start"
                generatedKey="joinedKey"/>
    </Context>
</Context>

The nested structure of <Context> tags is similar to the nested structure of XML elements in input XML files. However, the Mapping attribute does not need to copy whole XML structure, it can start at the specified level inside the whole XML file.

Defining the Mapping

• The Mapping definition is specified in the Mapping URL attribute or in the Mapping attribute.

• Every Mapping definition consists of <Context> tags. Each <Context> tag defines a mapping of particular XML subtree to record being sent to the specified output port.

• Each <Context> tag can surround a series of nested <Mapping> tags. These allow to map XML elements or attributes to Data Shaper fields.

• Each of these <Context> and <Mapping> tags contains some Context Tag Attributes and Mapping Tag Attributes, respectively.

XMLReader Context Tags and Mapping Tags

• Empty Context Tag (Without a Child) <Context xpath="xpathexpression" /> See Context Tag Attributes.

• Non-Empty Context Tag (Parent with a Child) <Context xpath="xpathexpression"> (nested Context and Mapping elements (only children, parents with one or more children, etc.) </Context> See Context Tag Attributes.

• Empty Mapping Tag (Renaming Tag) - xpath is used: <Mapping xpath="xpathexpression" /> - nodeName is used: <Mapping nodeName="elementname" /> See Mapping Tag Attributes.

XMLReader Context Tag Attributes

• xpath Required The xpath expression can be any XPath query. Example: xpath="/tagA/…​/tagJ"

• outPort Optional The number of an output port to which data is sent. If not defined, no data from this level of Mapping is sent out using such level of Mapping. Example: outPort="2"

• parentKey Both parentKey and generatedKey must be specified. The sequence of metadata fields on the next parent level separated by a semicolon, colon, or pipe. Number and data types of all these fields must be the same in the generatedKey attribute or all values are concatenated to create a unique string value. In such a case, the key has only one field. Example: parentKey="first_name;last_name" Equal values of these attributes assure that such records can be joined in the future.

• generatedKey Both parentKey and generatedKey must be specified. The sequence of metadata fields on the specified level separated by a semicolon, colon, or pipe. Number and data types of all these fields must be the same in the parentKey attribute or all values are concatenated to create a unique string value. In such a case, the key has only one field. Example: generatedKey="f_name;l_name" Equal values of these attributes assure that such records can be joined in the future.

• sequenceId When a pair of parentKey and generatedKey does not insure a unique identification of records, a sequence can be defined and used. Id of the sequence. Example: sequenceId="Sequence0"

• sequenceField When a pair of parentKey and generatedKey does not insure a unique identification of records, a sequence can be defined and used. A metadata field on the specified level in which the sequence values are written. Can serve as parentKey for the next nested level. Example: sequenceField="sequenceKey"

• namespacePaths Optional Default namespaces that should be used for the xpath attribute specified in the <Context> tag. Pattern: namespacePaths='prefix1="URI1";…​;prefixN="URIN"' Example: namespacePaths='n1="http://www.w3.org/TR/html4/";n2="http:\//ops.com/"'.

Note: Remember that if the input XML file contains a default namespace, this namespacePaths must be specified in the corresponding place of the Mapping attribute. In addition, namespacePaths is inherited from the <Context> element and used by the \ elements.

XMLReader Mapping Tag Attributes

• xpath Either xpath or nodeName must be specified in the <Mapping> tag. XPath query. Example: xpath="tagA/…​/salary"

• nodeName Either xpath or nodeName must be specified in the <Mapping> tag. Using nodeName is faster than using xpath. XML node that should be mapped to Clover field. Example: nodeName="salary"

• cloverField Required A Clover field to which XML node should be mapped. The name of the field in the corresponding level. Example: cloverField="SALARY"

• trim Optional Specifies whether leading and trailing white spaces should be removed. By default, it removes both leading and trailing white spaces. Example: trim="false" (white spaces will not be removed)

• namespacePaths Optional Default namespaces that should be used for the xpath attribute specified in the <Mapping> tag. Pattern:¨namespacePaths='prefix1="URI1";…​;prefixN="URIN"' Example: namespacePaths='n1="http://www.w3.org/TR/html4/";n2="http:\//ops.com/"'

Note: Remember that if the input XML file contains a default namespace, this namespacePaths must be specified in the corresponding place of the Mapping attribute. In addition, namespacePaths is inherited from the <Context> element and used by the \ elements.

XMLReader Input Mapping Attributes

• cloverField Required Output Clover field to input should be mapped. Example: cloverField="SALARY"

• inputField Required Input field to be used. Example: inputField="SALARY"

Reading Multivalue Fields

You can read only lists, however (see Multi-value Fields).

Note that reading maps is handled as reading pure string (for all data types as map’s values).

Example 22. Reading lists with XMLReader An example input file containing these elements (just a code snippet):

...
<attendees>John</attendees>
<attendees>Vicky</attendees>
<attendees>Brian</attendees>
...

can be read back by the component with this mapping:

<Mapping xpath="attendees" cloverField="attendanceList"/>

where attendanceList is a field of your metadata. The metadata has to be assigned to the component’s output edge. After you run the graph, the field gets populated by XML data like this (this will be seen in View data):

[John,Vicky,Brian]

Mapping Input Fields

If you use input port reading in discrete or source mode, you can map particular input fields to output fields using the inputField attribute.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<Context xpath="/rootPath" outPort="0">
 	<Mapping cloverField="field2" inputField="field2"/>
</Context>

Examples

Reading an XML File

This example shows the basic usage of XMLReader. You have a retail.xml file with data about your retail sale.

<?xml version="1.0" ?>
<orders>
    <order id="1">
        <firstname>John</firstname>
        <surname>Smith</surname>
        <emails>
            <email>[e-mail]</email>
            <email>[e-mail]</email>
        </emails>
        <item>
            <goodName>table</goodName>
            <items>1</items>
        </item>
    </order>
    <order id="2">
        <firstname>Ellen</firstname>
        <surname>Smith</surname>
        <emails>
            <email>[e-mail]</email>
        </emails>
        <item>
            <goodName>chair</goodName>
            <items>3</items>
        </item>
        <item>
            <goodName>tablecloth</goodName>
            <item>2</item>
        </item>
    </order>
</orders>

Create a list containing order_id, customer first name, surname and email(s).

Solution Create a metadata having 4 fields: order_id (integer), name (string), surname (string), email (string[]). Set up the attributes File URL, Implicit mapping and Mapping.

ATTRIBUTE	VALUE
File URL	${DATAIN_DIR}/retail.xml
Mapping	See the xml below
Implicit mapping	true

If you set Implicit mapping to true, fields name and surname are populated by values of corresponding elements. Content of the Mapping attribute:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<Context xpath="/orders/order" outPort="0">
    <Mapping cloverField="order_id" xpath="@id"/>
    <Mapping cloverField="email" xpath="./emails/email"/>
</Context>

The XMLReader will send following 2 records to its first output port.

1  John   Smith  [[e-mail], [e-mail]]
2  Ellen  Smith  [[e-mail]]

Mapping Input Fields to Output

This example shows reading an input file while some input fields are mapped to an output. Given a list of customers and paths to the files with orders.

C001|./file001.xml
C002|./file002.xml

Each file can contain one or more products:

<?xml version="1.0" ?>
<products>
    <product>A</product>
    <product>B</product>
</products>

Create a list with customers and products:

C001|A
C001|B
C002|E

Solution Use the File URL, Charset and Mapping attributes.

ATTRIBUTE	VALUE
File URL	port:$0.filename:source
Charset	UTF-8
Mapping	See the code below

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

<Context xpath="/products/product" outPort="0">
    <Mapping cloverField="productID" xpath="."/>
    <Mapping cloverField="customerID" inputField="ID"/>
</Context>

Sending Nested Elements to Different Output Ports

This example shows reading of an input file with nested elements. The nested elements on different levels are sent out to the different output ports. The input file countries-and-counties.xml contains a list of countries. Each country has a name and contains several counties. Each county has a name.

<?xml version="1.0"?>
<countries>
    <country>
        <name>England</name>
        <county>
            <name>Bristol</name>
        </county>
        <county>
            <name>Cumbria</name>
        </county>
        <county>
            <name>Devon</name>
        </county>
    </country>
    <country>
        <name>Scotland</name>
        <county>
            <name>Edinburgh</name>
        </county>
        <county>
            <name>Fife</name>
        </county>
    </country>
</countries>

Make a list of countries, and a list of counties with corresponding countries.

Solution Assign metadata country with the field countryName to the edge on the first output port. Assign metadata county with the fields countryName and countyName to the edge on the second output port. Use the File URL, Charset and Mapping attributes.

ATTRIBUTE	VALUE
File URL	${DATAIN_DIR}/countries-and-counties.xml
Charset	UTF-8
Mapping	See the code below

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<Context xpath="/countries/country" outPort="0">
    <Mapping cloverField="countryName" xpath="name"/>
    <Context xpath="./county" outPort="1">
        <Mapping cloverField="countryName" xpath="../name" />
        <Mapping cloverField="countyName" xpath="name"/>
    </Context>
</Context>

The records sent to the first output port are:

England
Scotland

The records sent to the second output port are:

England	 | Bristol
England  | Cumbria
England  | Devon
Scotland | Edinburgh
Scotland | Fife

Reading XML with Namespace

This example shows you how to read XML that contains different namespaces. A web page contains SVG graphics and links to other web pages. The links (<a>) are of two namespaces: xhtml and svg. Get URLs of the links from SVG image.

<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
    </head>
    <body>
        <svg width="1024" height="768"
            xmlns="http://www.w3.org/2000/svg" version="1.1">
            <a href="http://www.primeur.com">
                <circle cx="512" cy="384" r="80"/>
            </a>
        </svg>
        <p>
            <a href="http://www.example.com">www.example.com</a>
        </p>
    </body>
</html>

Solution Use the File URL, Charset and Mapping attributes.

ATTRIBUTE	VALUE
File URL	${DATAIN_DIR}/page.xhtml
Charset	UTF-8
Mapping	See the code below

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<Context xpath="/xhtml:html//svg:a"
         namespacePaths='xhtml="http://www.w3.org/1999/xhtml";svg="http://www.w3.org/2000/svg"'
         outPort="0">
    <Mapping cloverField="field1" xpath="@href"/>
</Context>

The output contains URL: http://www.primeur.com.

Best Practices

Implicit Mapping

To avoid typing lines like: <Mapping xpath="salary" cloverField="salary"/> Switch on the implicit mapping (see XMLReader Attributes) and use explicit mapping only to populate fields with data from distinct elements.

Avoid Unnecessary Context Elements

The <Context> element should be used only if you intend to send record corresponding to subtree to the output. Use

<Context xpath="/elem1/elem11" outPort="0">
    <Mapping cloverField="field1" xpath="elem111"/>
</Context>

instead of

<Context xpath="/elem1">
    <Context xpath="elem11" outPort="0">
        <Mapping cloverField="field1" xpath="elem111"/>
    </Context>
</Context>

Specify Charset

We recommend users to explicitly specify Charset.

See also

JSONReader XMLExtract XMLXPathReader XMLWriter Common Properties of Components Specific Attribute Types Common Properties of Readers