With Access 2002 or later, you can export a schema of the Access object, either embedded in the XML data file or as a separate XML Schema Definition (XSD) file. XML schemas are used to describe the structure of data in a common format that customers, other Web browsers, and any number of XML-enabled software programs can recognize. Specifically, schemas define 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. Access supports the XSD. XSD is a proposed World Wide Web Consortium (W3C) standard designed as a basic infrastructure for describing the type and structure of XML documents.

By using a schema, you can insure that the application receiving an Access-generated XML document understands the data and the defined structure of the document. Other organizations and applications can also provide their schemas to you so that you will know how to structure any data that you provide to them. Access 2002 does not support importing schemas.

XML syntax (the tags and their placement in a document) defines and describes the data in an XML document but doesn't indicate how the data should be displayed. In earlier applications and in some current uses, Cascading Style Sheets (CSS) were used to tell browsers how to display the XML data. However, a CSS isn't always a good choice because they are written in a specialized language which means that the developer has to use another language in order to write, modify, or understand the structure of the style sheet. A CSS merely allows you to specify the formatting of each XML element without much control over the output.

On the other hand, an Extensible Stylesheet Language (XSL) style sheet is considerably more flexible than a CSS file. It allows you to precisely select the data that will be displayed, to specify the order or arrangement of the data and to modify or add information. Additionally, it is written in a style similar to an XML document using a combination of XML-like tags and HTML to create a template for a specific style of output. You can export data using a XSL style sheet by choosing the Export Presentation option from the Export XML dialog box. Additional information about XSL style sheets can be found on the MSDN Web site.

You can export a database object as an XML document in several ways:

• You can export just the data from a table, query, datasheet, form, or report into an XML file. This data is saved to a file named <filename>.xml.
• You can export just the schema (data structure) of a table, query, datasheet, form, or report to an XML schema file. An XML schema file is a formal specification of the rules for an XML document, providing a series of element names, as well as which elements are allowed in the document and in what combinations. If you select to save the schema as XSD, the file is saved as <filename>.xsd.
• If selected, you can also can save the structure of a table, query, datasheet, form, or report into a file that describes the presentation and connection information. For forms and reports, this file is saved in an XML-based language called ReportML which provides presentation data as well as a data model for creating a data access page. For tables, queries/views, and datasheets, the presentation file is a spreadsheet-like template. This file is saved as <filename>_report.xml.
• In addition, when you choose to save the data as XML, you can specify that the data be transformed to a custom display format by using an existing .xsl file. If no .xsl file is specified, the data is saved in standard XML format. Note that if no data is selected for export then a presentation format is also unavailable. The file is saved as <filename>_report.xml.

ReportML is a "markup language" developed by Microsoft and specific to Access 2002 which can be used to describe Access database objects in XML. The ReportML language is made up of a set of tags that describe a form, report or data access page's properties, events, and attributes. When you export data from Access to an XML file by using the ExportXML method and set the appropriate flag, you can choose to save the structure of a form or report into a ReportML format. The ReportML file created by Access could be used to create a data access page.

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

• 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, there is a corresponding end tag. Empty elements can be denoted by a special shorthand tag. Again, XML tags are case-sensitive.

   Note   Access ReportML will not write out any empty tags.

• Elements do not overlap. In other words, start and end tag must be properly nested within other elements.
• Certain reserve characters are part of the XML syntax and will not be interpreted as themselves if used in the data portion of an element. You need to substitute a special character sequence (called an "entity" by XML) as follows:

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

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

where:

<?xml version="1.0"?>

<DATAROOT>

<CUSTOMER>

</CUSTOMER>

Notice that each tag set, such as

<CUSTOMER></CUSTOMER>

White space can be used throughout the document to enhance readability.

If a schema is specified while exporting from Access, then the XML documents created are considered to be valid XML document. This means that in addition to being well-formed, the documents conform to a defined schema.