The current 'composition' mechanism does not enable complex choreographies to be composed, nor 
does it support the specification of recursive choreography definitions.

The current 'perform' activity only allows the inclusion of simple 'atomic' choreographies that need to 
complete before the performing choreography can proceed. Generally complex choreographies will 
have a requirement to interact between the composed choreographies, to enable more complex higher 
level choreographies to be defined. 

In other words what is missing are appropriate and simple language constructs that enable recursive 
patterns to be defined as well as behavioral composition to be employed. The latter being what is 
needed to model more complex patterns of interaction using composed choreographies.

The current 'perform' activity is similar to the concept of (functional/alpha) replacement of a 
choreography definition, although it has a restriction that does not permit circular dependencies. 
Therefore it would not be possible for a perform activity to reference the choreography definition in 
which it is contained (or one of its parents). This recursive definition pattern would enable complex 
business interactions to be defined in a more abstract (simplified) manner. The only way that such a 
pattern could be modeled currently is through the use of variables and some form of repetition, which 
is really an implementation issue, whereas the CDL specification should provide a simplified 
representation of the business intent.

Where a particular CDL pattern needs to be generated into a specific implementation pattern at an 
endpoint, the CDL specification should include the definition of these endpoint generation rules - which 
can also be used to determine the impact on model checking of the implementation of a CDL 
specification.