VAST takes advantage of visual programming paradigm, which enables you to develop software by assembling and connecting reusable components called parts.

The construction from parts technology is based on well-established techniques from other industries such as manufacturing. Just as electronic chips can be combined to form a functional board, and functional boards can be combined to form a computer, software parts can be combined to form composite parts, and then further combined to form applications.

In VAST, a part is a self-contained software object with a well-defined public interface that establishes the features of the part.

There are three types of parts that you work with in VAST:

A part's public interface determines how it can interact with other parts. The public interface of a part consists of the following types of features:

Parts placed inside of other parts are called subparts. A part that contains other parts is called a composite part. All parts can be reused as subparts of composite parts.

A Properties view provides a way to display and set the attributes and other options associated with a part or connection. In addition to part-specific properties, you can set data validation, layout, drag and drop, and help information. For example, you can add an OK push button and define it as the default push button by opening the properties view for the Push Button part and setting the value of the showAsDefault property to true. A part's properties view is displayed using the Properties window for a part.

Connections define how parts interact with each other as well as how parts interact with scripts. You can make connections between parts, scripts, and other connections. A connection has a source and a target. The point at which you start the connection is called the source; the point at which you end the connection is called the target.

There are seven types of connections:

For more details about the different types of connections, see Connecting parts.

VAST includes a powerful object-oriented language named Smalltalk that you can use to extend your application logic. In VAST, a script is a series of Smalltalk statements that implement an action for a part.

You create and edit scripts using the Script Editor, which gives you direct access to the Smalltalk language. Scripts are associated with the parts in which they were created. VAST enables you to organize the scripts you write into categories.

Using Smalltalk code, you can easily extend the behavior of a VAST part. The following terms introduce you to some of the more common object oriented concepts you will encounter when using VAST. For an introduction to writing Smalltalk code, see the power of Smalltalk. For a more thorough understanding of this very robust programming language, refer to the Programmer Reference in the online documentation and VAST Platform publications found at Library web page.

A class specifies an object, including its data and behaviors. Methods, which are called scripts in VAST, are executable code that implements the behavior or logic of a particular class.

A VAST part is simply a class with some predefined data and behaviors that enables it to be edited visually in the Composition Editor.