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Ab initio Parameters

Parameters

A parameter is a value that you specify to control some part of an object’s behaviour.
The object can be a project, component, graph, subgraph, plan, and so on. You type in a value for a parameter (or click a button or select a value from a list), and thus specify the aspect of the object’s behaviour identified by the parameter’s name.

Every parameter has two main parts:
* the declaration of its name
* the definition of its value

Parameters also have attributes that specify various details about what type of value it can hold, whether the parameter is input or local.

The normal way to edit a component’s parameters is through the Parameters tab of the component dialog.

Graph, subgraph and project parameters are edited through the Parameters Editor.
Component parameters too can be edited with the Parameters Editor. Usually component parameters are edited through the components’ own dialogs (with Description, Parameters, Ports, and other tabs).

Parameter sets

Every object (component, graph, project, plan) has a parameter set consisting of all that object’s parameters.
The parameter set completely controls the object’s behaviour. It’s like turning the knobs on a piece of equipment: each parameter is like one knob, controlling one detail of the object’s behaviour.

When editing a graph in the GDE, you can view the complete parameter set of any component in the graph by selecting the component in the Parameters Editor’s left pane. A graph by default has no parameters of its own.

The complete component parameter set you see in the editor includes parameters not shown in the component dialog’s Parameters tab.

The GDE allows you to create files containing sets of values for a given graph’s input parameters (as well as any input parameters in the graph’s sandbox or common sandboxes). Such a file is called an input pset.

A component’s full parameter set includes all the values that can be set for it, in any of its tabs in its GDE dialog.

The component’s Description, Layout, Port and other tabs allow more convenient access to these values than would be possible by showing them as parameters in the Parameters tab. Nevertheless, all these values are parameters.

Parameter interpretation

The Interpretation you specify for a given parameter determines what kind of expression you can use to define its value. Above all, it determines how you can make references to other parameters in its definition.

Most of the interpretation methods offer, at a minimum, some form of $ substitution: by specifying the name of another parameter, preceded by a $, you effectively substitute the value of that parameter in the expression:

The big difference between the different interpretation methods is what they allow you to do in addition to simply referencing other parameters:

* Parameter Definition Language (PDL) interpretation
A full-featured notation that allows you to specify parameter references with $ or ${ } substitution, as needed. Also allows you to use inline DML or Korn shell expressions in parameter definitions.

* shell interpretation
Allows you to use shell syntax to construct parameter definitions (along with $ or ${ } substitution). Shell interpretation is not as versatile as PDL; PDL includes the capability of using shell interpretation along with other features that shell interpretation does not offer.

* $ substitution interpretation
Allows you to reference other parameters by specifying them in the $name form in the definition.

* ${ } substitution interpretation
Allows you to reference other parameters by specifying them in the ${name} form in the definition.

* constant interpretation
Declares that everything appearing in the parameter’s definition is to be interpreted literally; no substitution occurs at all.

In the GDE, we specify a parameter’s Interpretation method first by selecting it in the Parameters tab. Then we select the interpretation you want in the Interpretation box at the bottom of the tab.

In the Parameters Editor, we can set or change a parameter’s interpretation method by selecting the parameter and then editing the Interpretation attribute’s value in the editor’s right-hand pane.

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