Model elements

Model elements are the basic building blocks of models. There are three types:

• Tools: Geoprocessing tools are the basic building blocks of workflows in a model. Tools perform various operations on geographic or tabular data. When tools are added to a model, they become model elements.
• Variables: Variables are elements in a model that hold a value or a reference to data stored on disk. There are two types of variables:
  • Data: Data variables are model elements that contain descriptive information about data stored on disk. Properties of data that are described in a data variable include field information, spatial reference, and path.
  • Values: Value variables are values such as strings, numbers, Booleans (true/false values), spatial references, linear units, or extents. Value variables contain anything but references to data stored on disk.
• Connectors: Connectors connect data and values to tools. The connector arrows show the direction of processing. There are four types of connectors:
  • Data: Data connectors connect data and value variables to tools.
  • Environment: Environment connectors connect a variable containing an environment setting (data or value) to a tool. When the tool is executed, it will use the environment setting.
  • Precondition: Precondition connectors connect a variable to a tool. The tool will execute only after the contents of the precondition variable are created.
  • Feedback: Feedback connectors connect the output of a tool back into the same tool as input.

The diagram below shows how model elements are classified in ModelBuilder:

Element	Image	Description
Data variable		Existing data added to a model. Typically, data variables are the result of specifying a tool's input parameter. This existing data is sometimes referred to as project data.
Derived or output data variable		Derived or output data is new data created by a tool in the model. When a tool is added to a model, a variable for the tool's derived data is automatically created and connected to the tool. The tool creates a new dataset that is written to disk when the model is executed. The tool alters the input data when the model is executed. By default, the in/out derived data variable will have the same name as the input data but with a unique number appended at the end.
Value variable		Values that are input to a tool.
Value variable		Values that are the result of a tool. Derived values can be inputs to other tools. The Calculate Value tool, for example, outputs the result of a logical or mathematical calculation.
Tool		Built-in tool. These tools are built using ArcObjects and a compiled programming language like .NET. Built-in tools are typically system tools (those installed with ArcGIS) Iterators are tools that repeat the same operation or loop through a set of input data or values. Iterators work only within ModelBuilder, not in scripting. Learn more about iterators in ModelBuilder Model only tools functionally enhance ModelBuilder and only work within ModelBuilder, not in scripting. Learn more about Model Only tools The tool with this symbology is the Stop (Model Only) tool. This tool is only different than other Model Only tools in symbology in the model (looks like a red stop sign).
Tool		Script tool. These tools are created using the Script tool wizard and they run a script file on disk, such as a Python file (.py), AML file (.aml), or executable (.exe or .bat).
Tool		Model tool. A model is a collection of many tools connected together representing a workflow. A model tool can be run from its tool dialog box or added and used in another model or a script.

Description of model elements