Summary

Event providers are components that connect SQL-NS applications to real-world event sources. SQL-NS provides three built-in event providers: the FileSystemWatcherProvider, the SQLProvider, and the AnalysisServicesProvider. SQL-NS also includes a set of APIs you can use to build your own custom event providers.

Event providers can run as components inside the SQL-NS engine or as standalone programs. Event providers running in the SQL-NS engine are called hosted event providers. Those that run as standalone programs are called standalone (or nonhosted) event providers.

To use an event provider in your application, you either choose one of the built-in event providers, or build a custom event provider. You then configure your application to use the event provider by declaring it in the <Providers> section of your ADF.

If you're building a custom hosted event provider, you can implement it either as a continuous event provider or as a scheduled event provider that the SQL-NS engine invokes periodically. Both types involve writing a class that implements a SQL-NS interface and then providing the configuration information required for the SQL-NS engine to load this class at runtime.

You can build a standalone event provider as a dedicated program, as part of a bigger program with another primary purpose, or as SQL code that runs in the database. The particular form you choose for your application depends largely on the event source.

In this chapter, we looked at several ways to build event providers for the music store application. Some of these made more sense than others for this particular application, but it was important to look at all of them. In future chapters, we will use only one event provider with the music store application.