The goal of UNO (Universal Network Objects) is to provide an environment for network objects across programming language and platform boundaries. UNO objects run and communicate everywhere. UNO reaches this goal by providing the following fundamental framework:
- UNO objects are specified in an abstract meta language, called UNOIDL (UNO Interface Definition Language), which is similar to CORBA IDL or MIDL. From UNOIDL specifications, language dependent header files and libraries can be generated to implement UNO objects in the target language. UNO objects in the form of compiled and bound libraries are called components. Components must support certain base interfaces to be able to run in the UNO environment.
- To instantiate components in a target environment UNO uses a factory concept. This factory is called the service manager. It maintains a database of registered components which are known by their name and can be created by name. The service manager might ask Linux to load and instantiate a shared object written in C++ or it might call upon the local Java VM to instantiate a Java class. This is transparent for the developer, there is no need to care about a component's implementation language. Communication takes place exclusively over interface calls as specified in UNOIDL.
- UNO provides bridges to send method calls and receive return values between processes and between objects written in different implementation languages. The remote bridges use a special UNO remote protocol (URP) for this purpose which is supported for sockets and pipes. Both ends of the bridge must be UNO environments, therefore a language-specific UNO runtime environment to connect to another UNO process in any of the supported languages is required. These runtime environments are provided as language bindings.
- Most objects of Apache OpenOffice are able to communicate in a UNO environment. The specification for the programmable features of Apache OpenOffice is called the Apache OpenOffice API.
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