Declarative Programming

Just as a programming language lets a programmer tell a computer how and what to produce to the end user , the RDL tells the report server what data to use and how to lay it out. Now, there is a little trick here: Most programming languages communicate a what and a how to do something. There is no way to tell ASP.NET to produce a web page just by giving it a template. However, that is what the RDL does. The RDL communicates what the output is to look like and where the source data is to come from. This leaves the application free to decide how to generate the defined look and feel, regardless of the programming language or underlying architecture. This model is called the declarative model.

A producer application is an application that is used to generate RDL files. Business Intelligence Development Studio and Report Builder fall into this category. For most users, it is helpful to have a graphical user interface (GUI), although you can develop a report purely in your favorite text editor.

A consumer application is simply one that takes the RDL from the producer and creates the desired output. In its simplest form, it queries for the data and displays the results in the specified format. This is where a lot of the custom elements come in. Using the custom elements, it is possible to send instructions for one output format, which could then be ignored by all others.