Constants, Variables, and Parameters

StreamBase supports the use of constants, dynamic variables, and parameters in various places in your EventFlow modules. These constructions are discussed in the following sections.

  • Using Constants. You can define constants for use in any expression in operators and adapters in a module. In EventFlow programs, define constants in the Definitions tab of the EventFlow Editor.

  • Using Dynamic Variables. You can declare dynamic variables that can be referenced by name in expressions in operators and adapters in the containing module. In the declaration, you link each dynamic variable to an input or output stream in the containing module, and the variable's value is updated when a tuple is received on or emitted from the linked stream. Define dynamic variables for EventFlow applications in the Dynamic Variables tab of the EventFlow Editor.

  • Parameter Overview. This section helps distinguish module parameters and global parameters.

  • Using Module Parameters are declared at the module level, and their scope is the containing module. In EventFlow programs, declare module parameters in the Parameters tab of the EventFlow Editor. You can reference module parameters in expressions in any operator or adapter in the containing module. You can set values for module parameters in a number of ways.

  • String Values in Parameters suggests a standard way to pass string values to expression language contexts without using escaped quotes or quotes within quotes.

  • Container Parameters are declared at the container level, and their scope is every module within that container. In EventFlow programs, container parameters are referenced with the same syntax as module parameters. Module parameters of the same name take precedence over Container parameters within a module.