Besides displaying nodes and links, your
application will need to convey qualitative information on your
business data. Although diagrams such as business processes,
electrical networks, WAN networks, UML diagrams, and supply-chain
maps are all based on nodes and links, they do not look like
similar: each case requires notations and symbols that are
application-specific.
To define the notation for a particular application, JViews Diagrammer makes use
of a powerful model-based styling mechanism that relies on style
rules. Each rule defines conditions on the data model that trigger
graphical changes in the display. For example, you can define a
rule that draws a green rectangle when the
status
property of a node equals
fine
; and another rule that turns the rectangle to red when the
status
property equals
alarm
.
When you define a notation, you create the
basic symbols to be used for default situations. In an application
that deals with business processes, these symbols represent
activities, participants, messages, and so on. In a
telecommunications application, you need symbols for the many types
of network elements. Each basic symbol is defined by at least one
style rule.
Once the basic symbols are created, you then need to modify or
annotate them to reflect specific properties that you want to
display. You may want to change the background color to
red
when the
status
of a node equals
alarm
, or you may want to add a work-in-progress icon when an activity
is currently being performed. For each situation, you define a rule
that may complement or override the graphics effects defined by
more generic rules.
The styling mechanism is also used to
declare and customize options for the diagram as a whole, like the
use of layout algorithms and their parameters, or the use of a
background map and its source file and projection.
The set of style rules is stored in a style
sheet, and you can dynamically load a new style sheet while
keeping the same data and underlying data model. This facility is
useful when you need to adapt the display to a particular situation
or user profile. For example, the technical properties of a
business process can be hidden to the business analyst, and shown
only to the software engineer in charge of implementing the
process.
The style sheet syntax conforms to the CSS
syntax—a Web standard—but you need not bother with the details of
this syntax at this point. The separation of style sheets and the
data model from the diagram component means that you can build
several components based on the same data, with the same or
different styling, see the following figure.
A family of diagram components for a
data model
JViews Diagrammer eases the process of defining a notation with a
development tool called the Designer.
Using the Designer, you define the conditions for a rule using
natural language and you define the styling effects of the rule
through an intuitive panel that lets you change graphical
properties. While you are modifying rules or adding new ones, you
can select a rule in a tree view and see how the notation is
changing within a preview window.
JViews Diagrammer comes equipped with Business Process Management
Notation (BPMN) a standard notation for business processes that is
specified by the BPMI organization (see http://www.bpmi.org). This notation
provides a comprehensive set of symbols and sophisticated
swimlanes.