The second is the Data Set. For our purposes, the Data Set will contain a description
of the data we want to retrieve, such as SQL queries or custom code that will
populate the data in a scripted Data Source. At run time, the Data Set will actually
contain the data that is described by the SQL query. This is where it gets confusing.
In reality, The Data Set description and Data Set instance are two separate things;
however, for the purpose of report development, we don't need to concern ourselves
with that just yet.
The way this works is that Data Sets are dependent on Data Sources. Without a valid
Data Source, the Data Set has no way to retrieve data. That Data Source can contain
information on any number of different Data Sources, such as databases, flat text
files, XML data files, a special kind of Data Source called a scripted Data Source (that
lets BIRT know we will build our own Data Source by hand using Java or JavaScript),
or a custom data driver built using the Eclipse ODA framework. The Data Source
does the work because it knows how to communicate with the Data Source back end;
the Data Set tells the Data Source what to retrieve and then stores the results.
There are a couple of other data components in BIRT. The Report Parameter is a
way the report developer can interact with the report user.
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