The SDM engine is one of the most important pieces of JViews Diagrammer as it
controls the data-to-graphics mapping. There are four key elements
in the data-to-graphics mapping process:
- A data model that interfaces to the data to display or edit. This data model is completely independent of the GUI, and refers only to the business objects of your application.
- Renderers that style the diagram as a whole and the graphic objects in it. Renderers apply the styles specified in the style sheets.
- A grapher in which the graphic objects representing the data model are created as nodes and links. It provides the infrastructure that is minimally necessary to draw a diagram.
- Interactors that permit user actions on graphic objects. Common requirements are for zoom, pan, select, and object creation functions.
An example of the SDM Engine and the Data-to-Graphics Mapping is
shown in The SDM Engine and the Data-to-Graphics
Mapping.
The SDM Engine and the Data-to-Graphics
Mapping
As shown in The SDM Engine and the Data-to-Graphics
Mapping, the mapping between the data model and the graphical
representation is bidirectional:
- Data model to graphics: the rendering process is controlled by the style sheet, which lets you tell the SDM engine how you want each particular kind of data object to be displayed in the grapher. The rendering process is performed by specialized renderers.
- When the data model is loaded, the SDM engine explores it and creates graphic objects representing the nodes and links defined by the data model in the grapher.
- When the state of an object in the data model changes, the SDM engine updates the graphic object representing the modified data object.
- Graphics to data model: the editing process relies on built-in editing facilities that act directly on the underlying data model. The actions in an editing application are implemented by interactors. For example:
- When the user moves a graphic object (for example, in an editor), the SDM engine updates the geometric properties of the object in the data model.
- When the user expands or collapses a node (for example, in a navigation application), the SDM engine updates the expand/collapse status of the object in the data model.
The Data Model Interface
The SDM data model is the interface that
tells the SDM engine how to get the data to be displayed. The
SDM data model is an abstract description of a set of nodes and
links between nodes. Nodes and links have a user-defined type
(also called the tag), and a set of named properties.
JViews Diagrammer
provides prebuilt data models, and you can implement the data
model interface to connect your data.