STEM help / Distributable STEM

7.1.3 Comparing conventional and distributable authorisation

The copy-protection scheme for STEM is based on the concept of establishing the appropriate authorisation in order to run a model.  To fully understand the impact and power of D-STEM, it is helpful to compare the authorisation strategies used for conventional and run-time models.  The term model engine is used in the following sections to refer to the software component which is used to run a model and to generate the corresponding results.

Conventional authorisation

The C-STEM model engine always looks for authorisation when a model is run, so only licensed STEM users can run a conventional model, and only with a dongle.

Figure 1: Conventional model engine requires a dongle

Distributable authorisation

The D-STEM Editor has an additional facility which enables a licensed D-STEM user to ‘freeze’ the structure of a conventional model into an exported binary run-time model file.  This process is authorised by the presence of a D-STEM dongle, and this authority is ‘stamped’ into the run-time model at export time.  It is this digital stamp which identifies the model as a run-time model, and which authorises it to be re-run subsequently without a dongle, subject to limited modifications.

Figure 2: Distributable authorisation in run-time model

The scope of allowed modifications is selected by the D-STEM user at export time, but never extends to creating, renaming or deleting elements: the structure of a run-time model is fixed.  Subject to these constraints, any STEM Editor can be used to modify input assumptions without compromising the run-time status of the model.


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