XML Functions

Articolo
11/14/2006

You can more easily implement data exchange through XML formatting by using functions such as XMLUPDATEGRAM( ), CURSORTOXML( ), and XMLTOCURSOR( ). Whether you import XML data using XMLTOCURSOR( ) or export data using CURSORTOXML( ), your XML documents are valid when they are well-formed.

Note The MSXML parser is required to use XML functions in Visual FoxPro.

Well-Formed Documents

Any XML document produced by Visual FoxPro is well-formed, which means that it conforms to the basic rules of XML:

Each XML document must have a unique root element (an element encompassing the entire document).
All start and end tags match. XML tags are case-sensitive.
For each start tag, a corresponding end tag exists. Empty elements can be denoted by a special shorthand tag.
Elements do not overlap. In other words, start and end tags must be properly nested within other elements.

Certain reserved characters are part of the XML syntax and are not interpreted as themselves if used in the data portion of an element. You need to substitute a special character sequence, referred to as "entity" in XML, as follows:

Character	Data type	Entity encoding
& (ampersand) < (left angle bracket) > (right angle bracket) " (quotation mark) ' (apostrophe)	String String String String String	Replace with & Replace with < Replace with > Replace with " Replace with '

For other data types, entity encoding follows these rules:

Data type	Character and entity encoding
Date	Must follow the ISO 8601 format
Numbers	Punctuation must use U.S. English rules. For example, you must use a period as a decimal separator. Numbers can include exponents.
Boolean	False = 0, True = 1. (SQL XML returns 0 and1)
BLOB	Use MIME Base64 encoding

The following is an example of a well-formed XML document:

<?xml version="1.0"?>
<Data>
<ORDER>
 <CUSTOMER>Nancy Davolio</CUSTOMER>
  <ITEM>Mom&apos;s Boston Crab Meat</ITEM>
 <PRICE>$10.00</PRICE>
 <QUANTITY>1 Bottle</QUANTITY>
 </ORDER>
</Data>

where:

<?xml version="1.0"?>
Specifies a declaration that this is an XML document and gives the version number. The declaration is optional, but recommended in any XML document.
<ORDER>
Specifies the root element, which encompasses the entire document.
<CUSTOMER> ... </CUSTOMER>
Specifies a start tag and an end tag set, which together describes an element of data, in this case, the customer's name.

Note Each tag set, such as <CUSTOMER> ... </CUSTOMER>, has both start and end tags, is case sensitive, and is properly nested. Also notice the entity ' which will be transformed to an apostrophe (') when the data is imported by the receiving application. The apostrophe has a special purpose in an XML document, and can be misinterpreted if used directly in the text. The converted data will be displayed as Mom's Boston Crab Meat.

You can use white space throughout the document to enhance readability.

If you specify a schema while exporting from Visual FoxPro, the exported XML documents are considered to be valid XML. This means that in addition to being well-formed, the documents conform to a defined schema.

When you import XML using XMLTOCURSOR( ), Visual FoxPro uses an external or internal schema to determine the cursor or table structure. When no schema is provided, Visual FoxPro uses a "best guess" method to interpret XML data. This involves two passes through the XML, one to determine data structure and one to perform the actual conversion. Note that the XML, in addition to being well-formed, must generally conform to a format that can be interpreted as a table. Well-formed XML that is not easily deconstructed into a table format will fail to import.

Schemas

Schemas describe the structure of data in a common format that customers, other Web browsers, and any number of XML-enabled software programs can recognize. The description defines the rules of an XML data document including element names and data types, which elements can appear in combination, and which attributes are available for each element. Schemas provide a model for an XML data document which defines the arrangement of tags and text within all documents referencing the schema. Visual FoxPro supports XML Schema Definition (XSD), a basic infrastructure for describing the type and structure of XML documents.

By using a schema you can ensure that any XML document that is used to import or export data contains specific data and conforms to a defined structure. You can also provide the schema to other businesses and applications so that they can structure any data they provide to you and they, in turn, can provide their schema to you.

Visual FoxPro supports the W3C XSD schema format. Following is an example of XSD schema as output by CURSORTOXML( ) function:

<?xml version = "1.0" encoding="Windows-1252" standalone="yes"?>
<xsd:schema id="VFPSchema" targetNamespace="https://microsoft.com" xmlns="https://microsoft.com" xmlns:xsd="http://www.w3.org/2000/10/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata" elementFormDefault="qualified">
   <xsd:element name="atxm">
      <xsd:complexType>
         <xsd:all>
            <xsd:element name="ikey" minOccurs="0" type="xsd:int"/>
            <xsd:element name="nc00" minOccurs="0">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:decimal">
                     <xsd:precision value="10"/>
                     <xsd:scale value="4"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:element>
            <xsd:element name="mc03" minOccurs="0">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                     <xsd:maxLength value="2147483647"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:element>
            <xsd:element name="cc04" minOccurs="0">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                     <xsd:maxLength value="128"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:element>
            <xsd:element name="lc05" minOccurs="0" type="xsd:boolean"/>
            <xsd:element name="fc06" minOccurs="0" type="xsd:double"/>
            <xsd:element name="yc07" minOccurs="0" type="xsd:decimal"/>
            <xsd:element name="ic08" minOccurs="0" type="xsd:int"/>
            <xsd:element name="bc09" minOccurs="0" type="xsd:double"/>
            <xsd:element name="dc10" minOccurs="0" type="xsd:date"/>
            <xsd:element name="tc11" minOccurs="0" 
type="xsd:timeInstant"/>
            <xsd:element name="ts12" minOccurs="0">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:binary">
                     <xsd:encoding value="base64"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:element>
         </xsd:all>
      </xsd:complexType>
   </xsd:element>
   <xsd:element name="VFPData" msdata:lsDataSet="true">
      <xsd:complexType>
         <xsd:choice maxOccurs="unbounded">
            <xsd:element ref="atxm"/>
         </xsd:choice>
      </xsd:complexType>
   </xsd:element>
</xsd:schema>

The XSD schema format is based on the May 2, 1991 W3C Recommendation of the XSD Schema specification: "Primer, Structures, and Datatypes". For details, see http://www.w3.org/TR/2001/REC-xmlschema-0-20010502/ and related documents.

Currently, Visual FoxPro exports XML in the following formats:

**Element-centric **Each field in a resulting or source cursor or table is represented by a subelement of the top-level element.

<?xml version="1.0" encoding="Windows-1252" standalone="yes" ?>
<!-- Note targetNamespace in root (VfpData) element. If set to default (""), xmlns attrib is not written -->
<VfpData xmlns="https://www.microsoft.com">
   <alltypesxm>
      <ikey>2</ikey> 
      <nc00>1.1111</nc00> 
      <mc03>H1111111111111111111</mc03> 
      <cc04>H111111111111111111</cc04> 
      <lc05>true</lc05> 
      <fc06>-1111000</fc06> 
      <yc07>-111111111.1111</yc07> 
      <ic08>-11111111</ic08> 
      <bc09>-111111111111.1</bc09> 
      <dc10>1999-03-02T08:00:00</dc10> 
      <tc11>1999-03-02T09:01:01</tc11> 
      <ts12>AAAAAAAAAr8=</ts12>
   </alltypesxm>
</VfpData>

Attribute-centric The cursor is identified by the keyword "VFPData" and each field in a resulting or source cursor or table is represented by an attribute of the VFPData element.

<?xml version="1.0" encoding="Windows-1252" ?>
<!-- Note targetNamespace in root element -->
<VFPData xmlns="https://www.microsoft.com">
   <atxm_attr ikey="2" nc00="12345.1111" 
      mc03="H1111111111111111111" cc04="H111111111111111111" lc05="1" 
      fc06="-1111000.0000" yc07="-111111111.1111" ic08="-11111111" 
      bc09="-111111111111.100000" dc10="1999-03-02" 
      tc11="1999-03-02T01:01:01" ts12="AAAAAAAAAr0=" /> 
   <atxm_attr ikey="3" nc00="2.1111" mc03="H2222222222222222222"
      cc04="H222222222222222222" lc05="1" fc06="22220000.0000"
      yc07="2222222222.2222" ic08="222222222"
      bc09="222222222222.2200000" 
      tc11="2000-10-03T02:02:02" ts12="AAAAAAAAAr8=" /> 
</VFPData>

Raw Each row in a resulting or source cursor or table is represented by an XML element with the generic identifier "row", and each column value is mapped to an attribute of the row element where the attribute name is equal to the column name. This format is identical to Attribute-centric except for "row" as the name of the top-level element.

<?xml version="1.0"?>
<!-- Note no targetNamespace in root element -->
<VFPData>
   <row CustomerID="CACTU" CompanyName="Cactus Comidas para llevar"
      ContactName="Patricio Simpson" ContactTitle="Sales Agent"
      Address="Cerrito 333" City="Buenos Aires" PostalCode="1010"
      Country="Argentina" Phone="(1) 135-5555" Fax="(1) 135-4892"/> 
</VFPData>

Data Type Mapping

The following table describes the mapping of Visual FoxPro data to XSD types.

Visual FoxPro type	XSD type	Comments
Character	String with restriction `<xsd:maxLength value="128"/>`
Currency	Decimal
Numeric	Decimal with restriction `<xsd:precision value="10"/> <xsd:scale value="4"/>`	Precision is the number of digits excluding the decimal point.
Float	Decimal with restriction `<xsd:precision value="10"/> <xsd:scale value="4"/>`
Date	date
DateTime	timeInstant
Double	double
Integer	int
Logical	boolean
Memo	String with restriction `<xsd:maxLength value="2147483647"/>`
General	Not supported
Character (binary)	Binary with restriction `<xsd:encoding value="base64"/>`
Memo (binary)	Binary with restriction `<xsd:encoding value="base64"/>`

Condividi tramite

XML Functions

Well-Formed Documents

Schemas

Data Type Mapping

See Also

Risorse aggiuntive