U

Unicode: Unicode defines a set of letters, numbers, and symbols that SQL Server™ recognizes in the nchar, nvarchar, and ntext data types. It is related to but separate from character sets. See also Unicode standard.
Unicode standard: The Unicode standard expands the number of possible values for character data. By doubling the amount of storage space used for a single character, the Unicode standard exponentially increases the number of possible character values from 256 to 65,536. With this increased range, the Unicode standard includes letters, numbers, and symbols used in languages around the world, including all of the values from the previously existing character sets.
Uniform Resource Identifier (URI): A superclass that includes both URNs and URLs. Presently, URI means URL in nearly all cases when discussing XML, although it is expected that URNs will become more numerous in the future. The URI supplies a number or name that can identify an element or attribute in a universally unique way. URIs are a slightly more general scheme for locating resources on the Internet that focuses more on the resource and less on the location. In theory, a URI could find the latest copy of a mirrored document or locate a document moved from one site to another.
Uniform Resource Locator (URL): The set of URI schemes that have explicit instructions on how to access the resource on the Internet. URLs are uniform in that they have the same basic syntax no matter what specific type of resource (Web page, newsgroup) is being addressed or what mechanism is described to fetch it.
Uniform Resource Name (URN): Identifies a persistent Internet resource. A URN can provide a mechanism for locating and retrieving a schema file that defines a particular namespace. While an ordinary URL could provide similar functionality, a URN is more robust and easier to manage for this purpose because a URN can refer to more than one URL. URNs are not location-dependent as URLs are.
Universal Data Access: A tool- and language-independent set of interfaces for providing access to a variety of information sources including relational and nonrelational databases. The Microsoft Data Access Components enable Universal Data Access. For more information, see the site http://www.microsoft.com/data.
URI: See Uniform Resource Identifier.
URL: See Uniform Resource Locator.
URN: See Uniform Resource Name.
user-defined data type: A data type, based on a SQL Server data type, created by the user for custom data storage.
user services: The part of an application's architecture that presents information to and gathers data from the user. For more information, see User Services Described.
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