Microsoft SQL Server XML and Web Application Architecture.
Microsoft SQL Server 2000 has has added many new features that SQL Server 7 did not have, among them a series of new XML technologies called SQL Server XML. This technology suite contains many improvements, enhancements, and features that make SQL Server a more Web-friendly application.
SQL Server XML can be used to extend, enhance, or even replace the architecture of a Web application. The new features are comprised of two main components: .
1. Database components, that allow the database to read, process, and write XML .
2. SQL Server XML Internet Server API (ISAPI) application, which allows access to the database over HTTP .
With XML support in SQL Server 2000, you can query SQL over HTTP with a URL, bring the data down to the browser, and manipulate it on the client machine. By using Internet Explorer 5.0 and XSL to convert the XML to HTML, it is possible to lighten the load on the database server. Going one step further, by using Vector Markup Language one can create drawings on the fly using the data from your SQL queries.
Two architectures are always at work: the logical architecture, which is an organizing concept that drives the factoring of the application, and the physical architecture, which represents the way the application is implemented. The physical architecture appropriate for any given logical design will vary according to the situation.
One type of logical architecture is based on Microsoft n-tier guidelines. This architecture is composed of common operations performed by Web applications.
Figure 1. Logical architecture.
Using this logical architecture, the application is divided into five layers. Farthest from the client is the data layer, which stores the information needed by the application. Directly above the data layer is the data access layer, which abstracts the data from its representation in the database and contains routines common to all database operations.