| Platform SDK: CDO for Windows 2000 |
Microsoft CDO for Windows 2000 enlists the use of Uniform Resource Identifiers (URIs) to qualify or scope field names and their semantic definitions. Each field accessed through a Fields collection is comprised of a namespace prefix and a local name. The namespace prefix is a URI reference used to qualify or scope the semantic definition of the property. For example, the subject field for a message has two representations: one with non US-ASCII characters encoded using the mechanism defined in RFC 1522, and another where these characters are decoded into native, UNICODE characters. By using namespaces, one can identify which semantic definition is intended when the "subject" for the message is requested. In this case, the subject field defined within the urn:schemas:mailheader: namespace is defined to be the US-ASCII string value of the field, and the subject field defined within the urn:schemas:httpmail: namespace is the native, UNICODE version.
The following URIs are used as namespaces with Microsoft CDO for Windows 2000:
http://schemas.microsoft.com/cdo/configuration/
http://schemas.microsoft.com/exchange/
http://schemas.microsoft.com/cdo/nntpenvelope/
http://schemas.microsoft.com/cdo/smtpenvelope/
urn:schemas-microsoft-com:office:office
When accessing fields within a Fields collection on an object, the full name of the property must always be used. String constants are provided for each field name to help simplify accessing fields in Fields collections. For example, to retrieve the Content-Type for a message, you would retrieve the urn:schemas:mailheader:content-type field from the Message object's IMessage.Fields collection.
Note This mechanism is based upon the World Wide Web Consortium (W3C) Namespaces in XML Recommendation and is used primarily to provide uniformity and forward-compatibility with the Microsoft CDO for Exchange 2000 COM component. Files and their associated properties stored in the Microsoft Exchange 2000 Server Information Store can be accessed using the WebDAV protocol which is a specification for extensions to the Hypertext Transfer Protocol (HTTP) Version 1.1. The WebDAV extensions define XML as the wire-transfer format for properties and it specifies URI namespace references (Namespaces in XML) as the mechanism whereby heterogeneous sets of properties for a particular resource (file or item) can be qualified and rendered unambiguous. For more information, see the Microsoft Exchange 2000 Server documentation. The latest Namespaces in XML Recommendation can be found at http://www.w3c.org/TR/REC-xml-names.