Boxed Context

This icon in the top right corner of the Decision or Business Knowledge (BKM) Model element indicates that it is implemented as Boxed Content. A Boxed expression is typically used in the circumstance that a Literal Expression would result in complex and difficult to understand logic. Like the Decision Table its tabular form makes it easier for business managers and other non-technical stakeholders to understand.

Fundamentally a Boxed Context is a collection of context entries, presented in the form of a table, followed by a final result expression. These context entries consist of a variable paired with a value expression, and can be thought of as intermediate results that can be used within the value expression of any subsequent context entry.  This allows for complex expressions to be decomposed into a series of simple expressions, with the final result being evaluated in a much simpler form.

This image shows the key parts of the DMN Expression window for the definition of Boxed Context. Recall that there are three other types of value expression, and the window will appear differently for each of them.

The value expression of a context entry can be either a Literal Expression or an Invocation and can make use of any available inputs, such as parameters (to a BKM element), InputData or decision results, as well as any previously defined context variables. The final result of a Boxed Context is determined by working through each context entry in turn, evaluating the value expression and assigning its result to the variable, then finally evaluating the result expression. The result expression can also make use of any input or local variable, but it must be able to be evaluated to provide a result.