# Overview

Today’s software applications are more capable and easier to use than ever before. Yet as their feature sets have grown in complexity and size, they have become increasingly difficult and costly to engineer, maintain, and upgrade. Adding new features always runs the risk of introducing new, sometimes intractable bugs and endangers backward compatibility with earlier versions. In addition, most applications are monolithic, providing rich sets of features but no easy way to add missing features or remove unneeded ones. Applications that do support adding and removing features in the form of plug-in components may expose their services to sibling applications from the same vendor but rarely to those from entirely different vendors. As a result, applications from different vendors typically work together poorly or not at all.

Operating systems have a related set of problems. Because most operating systems are not sufficiently modular, upgrading, replacing, or overriding existing services in a clean, flexible way is difficult. Like application developers, systems vendors face the difficult choice of foregoing or compromising needed improvements in order to maintain backward compatibility, or disenfranchising existing users in order to move the technology forward. These are choices that serve no one.

Software developers have recognized for some time that object-oriented programming offers promising solutions to several of these problems. By encapsulating data and functions in a single entity, then providing access to this rich content through a single reference, or pointer, object-oriented programming makes it possible to break down monolithic applications into functional modules, or components, that can be added or removed as they are needed. Moreover, object-oriented programming can potentially reduce the expense of implementing new objects by enabling them, through mechanisms such as inheritance, polymorphism, and aggregation, to make use of the capabilities built into already-existing objects.

Even so, object-oriented programming has yet to reach its full potential because no standard framework has existed through which software objects created by different vendors could interact with one another within the same address space, much less across process, machine, and network boundaries. Once you have broken down software into manageable, interchangeable components, you need some way for those components to communicate. That’s where OLE comes in.

OLE provides a standard conceptual framework for creating, managing, and accessing object-based components that provide services to other objects and applications. OLE components can exist as parts of an operating system or application, or as stand-alone entities, and the services they provide can be most anything that operating systems and applications currently supply. You can use OLE components to expose both data and services to programs created by other vendors and write your own applications in such a way as to take advantage of services provided by others. You can also extend or customize basic OLE services to suit the needs of your objects and applications while guaranteeing that they continue to work with other OLE components.