17. A computer implemented method for facilitating rich customization of visualizations based upon a declarative model, comprising: receiving a data file or stream in compliance with an extensible declarative model defining a set of source descriptors, a set of transform descriptors, and a set of visualization descriptors, a source descriptor declaratively describes a data source, a transform descriptor declaratively describes an operation that acts on the data source for providing a result, and a visualization descriptor declaratively describes at least one of an appearance, a behavior, or one or more features of a visual representation of the result; accessing the data source described by the source descriptor; transforming the data source by applying the operation described by the transform descriptor; rendering the visual representation of the result described by the visualization descriptor; and displaying the visual representation in a visualization canvas.
17. A computer implemented method for facilitating rich customization of visualizations based upon a declarative model, comprising: receiving a data file or stream in compliance with an extensible declarative model defining a set of source descriptors, a set of transform descriptors, and a set of visualization descriptors, a source descriptor declaratively describes a data source, a transform descriptor declaratively describes an operation that acts on the data source for providing a result, and a visualization descriptor declaratively describes at least one of an appearance, a behavior, or one or more features of a visual representation of the result; accessing the data source described by the source descriptor; transforming the data source by applying the operation described by the transform descriptor; rendering the visual representation of the result described by the visualization descriptor; and displaying the visual representation in a visualization canvas. 18. The method of claim 17 , further comprising at least one of the following acts: constructing a set of visual elements for each of the set of source descriptors, the set of transform descriptors and the set of visualization descriptors; presenting a visual element from the set of visual elements as a selectable object in a palette; populating a design canvas with objects selected from the palette; or configuring the visualization descriptor based upon the objects selected from the palette.