Defining the Configuration-Dependent Data Parameters

Parameters are introduced by using the *Features construct. The construct tag of the *Features construct identifies the parameter (or defines the parameter name, which is also referred to as the feature name).

The content of the *Features construct can consist of one or more *Option constructs. The *Option constructs define the allowed values or states that the parameter can be in. The construct tag of the *Option construct identifies an allowed value or state. This construct tag is also called the option name.

For example,you can define a parameter named Today that can take a day of the week as its value, as the following code example shows.:

*Feature: Today
{
  *Option: Sunday{}
  *Option: Monday{}
  *Option: Tuesday{}
  *Option: Wednesday{}
  *Option: Thursday{}
  *Option: Friday{}
  *Option: Saturday{}
}

In the preceding example, the Today parameter can take only one value at any given time. Today cannot be both Sunday and Tuesday. However, not all parameters are not limited to exclusive values; they can take one or more values at a time. For example, if you have a robot that can hold more than one color of pen in its hand at the same time, you can define a PenColors parameter to describe the colors that are currently in its hand. You might specify PenColors: (Red AND Green AND Yellow) and that might be perfectly valid.

The *UIType reserved directive enables you to designate whether a parameter can take only a single value at any time (PICKONE) or whether multiple values can be assigned to that parameter at a given time (PICKMANY). The *UIType directive is positioned as a child entry of the *Features construct.

Note   GDL does not allow "nothing" to be assigned to a parameter. Thus, to describe the robot holding no pens, you must declare an option called None or Off for PICKMANY parameters. The option name that is used is not important; you can designate which option is assigned this property by using the *NoneOption directive. The option that *NoneOption designates is not compatible with any of the other options.

You can define as many *Feature constructs as you have parameters. All *Feature constructs must reside at the root context. The root context has no parent construct.