Nevron Gauge for Reporting Services is a custom report item. In order to better understand how to work with it and bind it to data you should have a general understanding of custom report items and the data model they use.

Each custom report item has a design model and runtime state. The design model defines how it merges with the actual data, which is provided at runtime. The runtime state represents the report item when the data has been processed by reporting services and merged with the design model of the item. Custom report items are similar to the Matrix report item. Custom report items are composed by hierarchically organized row and column data groupings (see Custom Report Items Processing for a complete discussion).

Because not every Matrix model is suitable for a gauge, Nevron Gauge for Reporting Services uses a simplified model, which is better suited for this purpose. Figure 1 illustrates the design model of the gauge:

 

Figure 1 - The Gauge Data Model

There are three types of data groupings - root category, categories and gauge parts.

Collectively, the root category and the category data groupings define how data cells expand in the column direction. Category data groupings are dynamic - they represent a grouping of the data based on some expression conditions (typically a field value). At runtime, each category data grouping expands to one or more group members.

The root category is static - at runtime there is again only one root category. The root category is always present and cannot be edited. That is why the category data groupings are optional - the gauge always has one leaf column data grouping serving as a column placeholder for the gauge part data cells (see below).

The column hierarchy is simple and represents a parent-child chain. Each category data grouping has exactly one parent, except the root category, which has no parent. Each category has exactly one child category, except the last category, which has no children. For example: Category 1 is a parent of Category 2 and Category 2 is the one and only child of Category 1. Moving categories up and down from the visual interface in fact makes changes in this parent-child chain (for example: moving Category 2 up makes Category 2 the child of the root category. Category 1 becomes the only child of Category 2 and if Category 2 had a child it becomes a child of Category 1). The root category always stays on top.

Gauge part data groupings are static - at runtime exactly one data grouping member is created for each gauge part. A gauge part is a row placeholder for a data cell. Gauge parts are automatically created/destroyed for gauge axes, ranges, pointers and numeric display values. The data cell associated with a gauge part contains the needed properties for the respective gauge element (for example: a gauge part data cell created for a gauge axis will have min and max properties, a gauge part data cell created for a gauge pointer will have a value property etc.).

At runtime, the data cell for a gauge part will span all leaf category members. This generates a set (list) of values for each data cell property. The gauge element, owning the gauge part, extracts a single value from this set by using a statistical formula - see Gauge Formulas for more information.