Services are method-like units of logic that operate on documents. They are executed by Integration Server. You build services to carry out work such as extracting data from documents, interacting with back-end resources (for example, submitting a query to a database or executing a transaction on a mainframe computer), and publishing documents to Universal Messaging. Integration Server is installed with an extensive library of built-in services for performing common integration tasks. Adapters and other add-on packages provide additional services that you use to interact with specific resources or applications. webMethods graphical implementation language, flow, enables you to quickly aggregate services into powerful sequences called flow services.