Modeling Issues

This section identifies some general modeling issues encountered and the OMS approach to resolving the issues.  The approach selected has been pragmatic (given limited time and resources) and is not advocated as a general approach.

Business Rules.  There are a number of tools and methods for identifying and documenting business rules, but these tools are oriented towards extending.  Some rules fit naturally into an Object Oriented Model (e.g., pre and post conditions on methods, derivations as methods).  However, some rules do not fit (e.g., invariants, definitions).  Should business rules be defined in a central repository or defined as part of individual classes? For OMS, the analysts are defining derivations and pre and Post conditions as part of the class definition.  data Invariants are being defined in the database.  However, no central repository of business rules will be captured. 

Long Lived Transactions.  Applications for loans and insurance go through a complicated process (verification of information, several levels of approval, different types of clearances, final acceptance).  This process may also have several financial effects( obligating and de-obligating funds, transfer to the applicant, transfer to reserve account).  In OMS, this processes is modeled as a combination of workflow, as set of usage scenarios and class definitions.  However, there is a need for some higher level concept to map to the application process. 

Interfaces versus Objects.  OMS is using OMT which identifies object types.  However, the OMS target architecture will implement services as sets of related interfaces.  Should interfaces be defined during modeling or are they an implementation specific construct?  How difficult is it to map from object types and instances to interfaces?  OMS has decided that this issue is a design consideration.

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