XML in 6.5 and 7.0?
In October, Microsoft released a technology preview for XML. If you're familiar with the Internet Database Connector (IDC) approach to working with Web sites and databases, you'll quickly be saying, "Here we go again."
In this preview, Microsoft lets you use a browser to either pass a SQL operation as a parameter or specify a template file that contains the operation you want to perform. To call the XML interface, you use a URL that passes the SQL statement to a parser. The parser sends the statement to SQL Server and sends back XML-formatted data.
In addition to this query process ability, Microsoft lets you build and specify an output template file that is used to format the output as needed by the client making the call. This procedure is just like the HTML Extension files (HTX) of yore, the formatting files used in the early days of Microsoft databases on Web sites.
Although I respect Microsoft for implementing XML because XML provides connectivity to SQL Server 6.5, 7.0, and beyond, I'm concerned that this XML implementation will reintroduce many of the problems that still plague users who embraced the concept of IDC and HTX database integration for Web sites before. Too many Web sites still use the IDC approach to access databases, despite the fact that this approach is slow, difficult to manipulate, and not very dynamic.
The Basics of XML
Here are several key features of XML, specifically Microsoft's implementation—the technology preview—of XML for SQL Server. You can use the Microsoft preview to help you understand the following XML elements:
- Grams are commands that you send to the database engine, such as INSERT, UPDATE, and DELETE. You can send multiple statements in a single gram. You use special tags in the gram, including Before, After, and Sync. Sync is what's now known as a transaction; all items within a sync section are considered a single transaction. You use the Before and After tags to indicate what needs to be done (after) and what the data should look like before the change (before). Think of the Before tag as a WHERE clause.
- You use a URL to issue standard SELECT statements. In this URL, you can pass in the SELECT statement and indicate the formatting of the data output. By default, the data will come back as a block of text in XML format that your client application can use.
- You can see the output of the statements, and you can work with available formatting options.
I recommend that you download, install, and use the XML technology preview from Microsoft's SQL Server Web site (http://msdn.microsoft.com/ workshop/xml/articles/xmlsql/), but I can't stress enough that you should use this preview only to learn XML and its use. Don't use this technology preview in a production environment. We all build sample applications that turn out to be so helpful that people use them in production. Don't go there with this preview. Use it as Microsoft presents it, as a learning and testing tool for your environment.
Future of XML
I'm concerned that XML, Extensible Style Language (XSL), and other facets of XML will introduce additional developer overhead. Developers already use OLE DB and ODBC to code SQL statements. At best, introducing XML adds a new layer to the process. At worst, XML adds a layer that won't be fully integrated into the database engine. This lack of integration will shift responsibility for the database language elements back to the developer, which is the situation Microsoft tried to avoid by introducing ODBC and OLE DB. I hope that Microsoft will make the true XML interface (not the technology preview) easier to use without giving up the middleman layers provided by OLE DB and such.
XML is here to stay. It's an easy way to exchange information between sources, and it will enhance the usability of many tools, such as reporting tools, because the tools will know more about the data being passed to them. The SQL Server community is in the foundational stages of using XML. We're learning the language, seeing it in action, putting it through its paces, and trying to understand it.
Here's one last thought about XML. Assuming that XML is truly a success and breaks down the barrier between the client and server software (and the tiers in between), what will XML do to the database server wars? If the data and the interface to that data are identical between engines, you'll need to remove a level of variables from the database engine selection criteria for a given project. Now that will be interesting.
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