Modelica is a freely available, object-oriented language for modeling of large, complex, and heterogeneous physical systems. From a user’s point of view, models are described by schematics, also called object diagrams. Examples are shown in the next figure:

A schematic consists of connected components, like a resistor, or a
hydraulic cylinder. A component has *connectors* (often also called
*ports*) that describe the interaction possibilities, e.g., an
electrical pin, a mechanical flange, or an input signal. By drawing
connection lines between connectors a physical system or block diagram
model is constructed. Internally a component is defined by another
schematic, or on “bottom” level, by an equation-based description of
the model in Modelica syntax.

The Modelica language is a textual description to define all parts of a model and to structure model components in libraries, called packages. An appropriate Modelica simulation environment is needed to graphically edit and browse a Modelica model (by interpreting the information defining a Modelica model) and to perform model simulations and other analysis. Information about such environments is available at www.modelica.org/tools. Basically, all Modelica language elements are mapped to differential, algebraic and discrete equations. There are no language elements to describe directly partial differential equations, although some types of discretized partial differential equations can be reasonably defined, e.g., based on the finite volume method and there are Modelica libraries to import results of finite-element programs.

This document defines the details of the Modelica language. It is not intended to learn the Modelica language with this text. There are better alternatives, such as the Modelica books referenced at www.modelica.org/publications. This specification is used by computer scientist to implement a Modelica translator and by modelers who want to understand the exact details of a particular language element.

The Modelica language has been developed since 1996. This document describes version 3.4 of the Modelica language. A complete summary is available in section E.1.