SQL SERVER AS A PLATFORM FOR WEB SERVICES required for full functionality. Not only is TDS a proprietary protocol, but it needs some special firewall configuration to work over the Internet. A specific network port (port 1433 in the default case) needs to be open on any firewall in order to communicate through TDS over TCP/IP. In addition, later versions of SQL Server use integrated security using NTLM or Kerberos security systems. NTLM will not pass through firewalls, and Kerberos will only with great difficulty. Most firewall administrators, with good reason, won t open the ports needed for users to connect directly to SQL Server over the Internet. Web Services expose a standard mechanism for communication that uses standard protocols and a common message format. The network protocol most often used is HTTP. The message format is known as SOAP. Web Services can be produced and consumed by any platform with an HTTP stack and an XML stack. It has become a popular means of communication among unlike systems and may displace proprietary protocols over time. SQL Server 2000 allowed communication via HTTP by using Internet Information Server and an ISAPI DLL. This DLL allowed users to issue HTTP requests (subject to security, of course) to well-known endpoints exposed with XML-based files known as templates. The ISAPI application parses the template and uses TDS to talk to SQL Server. These templates could use SQL or XPath queries, embedded in SQL. The result of these queries was XML in a well-known format, and this XML could also be postprocessed with XSLT inside the ISAPI DLL. In addition, with the proper configuration of the ISAPI application, users could enter endpoints that corresponded to SQL or XPath queries via a URL parameter. Through a number of post SQL Server 2000 Web releases, known as SQLXML, the functionality of the ISAPI application was expanded to support direct posting of updates in XML formats (known as DiffGrams and Update- Grams) and producing the XML output on the client side, allowing additional postprocessing capabilities. SQLXML 3.0 expanded the capability of the ISAPI DLL to include the production of SOAP packets, therefore exposing SQL Server through IIS as a Web Service. Any stored procedure, user-defined function, or template query can be exposed as a SOAP endpoint. Output is available in a variety of formats, some optimized for the .NET consumer, but all using the SOAP protocol. The ISAPI application was also expanded to produce Web Service Description Language (WSDL), a standardized dialect of XML that describes the format and location of a Web Service. This allowed any

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