Object-Based Programming

Abstract

Distributed systems can be naturally modeled in Maude as multisets of entities, loosely coupled by some suitable communication mechanism. An important example is object-based distributed systems in which the entities are objects, each with a unique identity, and the communication mechanism is message passing.

Core Maude supports the modeling of object-based systems by providing a predefined module CONFIGURATION that declares sorts representing the essential concepts of object, message, and configuration, along with a notation for object syntax that serves as a common language for specifying objectbased systems. In addition, there is an object-message fair rewriting strategy that is well suited for executing object system configurations. To specify an object-based system, the user can import CONFIGURATION and then define the particular objects, messages, and rules for interaction that are of interest. In addition to simple asynchronous message passing, Maude also supports complex patterns of synchronous interaction that can be used to model higherlevel communication abstractions. The user is also free to define his/her own notation for configurations and objects, and can still take advantage of the object-message rewriting strategy, simply by making the appropriate declarations. All this is explained in detail below.

Furthermore, Maude also supports external objects, so that objects inside a Maude configuration can interact with different kinds of objects outside it. At present, the external objects directly supported are internet sockets; but through them it is possible to interact with other external objects. In addition, sockets make possible distributed programming with rewrite rules. External objects are discussed in Section 11.4. A substantial case study using sockets to build a mobile language is presented in Chapter 16.

As discussed in Chapter 19, Full Maude provides additional support for object-oriented programming with classes, subclassing, and convenient abbreviations for rule syntax.