ABSTRACT
This chapter introduces a core metaphor that drives the interaction of code and data in computer programming: objects. It presents a simple inheritance relationship between line-like geometric elements. The chapter provides more elaborate examples, including a family of geometric types that manage access to a collection of Points. Modern object-oriented programming presents a more detailed model for the structure of data, and a more profound set of implications for conceptualizing software development. In contrast to values that are represented by objects that reside within the active model, a literal is a value that is explicitly defined in code. The evaluation of a statement begins with the most basic elements of expressions, sometimes termed atoms, which includes both the interpretation of literals and the retrieval of variables. Expressions are formed of chains of object references and operators which combine into larger statements, typically within a single line of code.
