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The implementations of components above, either individual or composite, all form reusable units that can be run multiple times in different environments (in much the same way as you have multiple instances of a Java class). A component or composite becomes . A composite, with its configuration information, gets packaged into a deployable unit called a contribution which gets contributed to the domain. An SCA Domain represents the SCA runtime. Domain configuration is the overall configuration for service dependencies, properties, policies. A domain is a logical view of the running applications or a coherent grouping of components that are working together, connected to each other using SCA wiring. The composites get instantiated when it is actually used in an SCA environment. This is done by using it as part of the assembly of an SCA Domain.

SCA Domains can vary in size from the very small to the very large:

• a very small domain could be one within a test environment inside an IDE
• a medium sized domain could be a single server or small cluster supporting a single application
• a large domain could describe all the services within a department or company

A domain is a logical view of running applications or a coherent grouping of components that are working together, connected to each other using SCA wiring. In a large domain there may be all sorts of policies about where components can run and how they connect to each other or to external services. However, during development one is not concerned with all this. The code is packaged and made available for deployment. Tuscany provides some build-time tools to help with packaging. For example, a war Maven plugin to package a self contained web application.

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you develop an app and package it as a contribution. The app may consist of one or more composites.
Contribution is an installable piece. So, you then install the contribution and then activate the deployed composites in the contribution. The SCA domain is the logical view of running applications that can span multiple SCA runtimesSCA Java supports contributions in the form of JAR or filesystem.