The principle of a run-time model is that an end-user should be able to make limited modifications and still be able to run that model (without a dongle) with a run-time model engine. The run-time status of a model will always be revoked if the end-user creates, renames or deletes a model element, thus ensuring that the structure of the model remains fixed. However, within this absolute constraint, the D-STEM user can choose (at export time) how much flexibility the end-user will have. The following sections discuss the various export options available in the Export Run-Time Model dialog.
External links
The easiest way to present and limit the key parameters for a model is to link them from a spreadsheet or database. Select Allow Update to enable a model to be updated with respect to revised assumptions in such external files.
Selecting Copy External Files simply automates the process of copying files referenced by (relative) external links into the export directory.
Opaque models
If you are presenting the key inputs to a model in a spreadsheet, then it may well be easier for end-users who aren’t familiar with STEM if you design the model to be updated and run from that spreadsheet, using the Implied Logic STEM add-in for Microsoft Excel – see 7.3.6 Running STEM from Excel – which is one of the optional distributable software components.
The extent to which you would like the actual structure and assumptions in a model to be apparent depends very much on whether the intended end-user is a colleague or a customer. Even if you are happy for your customer to see inside a model, you may not be so happy for your customer’s alternative suppliers to (potentially) have this insight!
In order to avoid a model being exported with greater visibility than is intended, the default Editor Access setting protects your intellectual property by determining that the exported run-time copy cannot be loaded into the STEM Editor at all.
This option is designed to be used with a model which can be run from an external file, and treats STEM rather like a black box. Any attempt to load such a model will be rejected by the Editor as follows:
Note: If a model is exported with Editor Access = None, all structural detail is suppressed from the .dtl file, and the corresponding .icp file is not copied to the export directory at all.
The Results Program can still be used to browse the results of an opaque model, but only at the Network level. Any attempt to display results for individual elements will be rejected as follows:
Read-only models
If you are keen to communicate the structure of a model which is driven from pre-defined and limited assumptions in an external file, then selecting Editor Access = Read-only will allow the model to be loaded into the Editor in such a way that any modification within the Editor will revoke the model’s run-time status. When the model is first loaded, the words ‘Read-Only Run-Time’ will appear after the model name in the main Editor window caption, as shown below.
Any modification to the model whatsoever will result in the end-user being asked to confirm the imminent loss of run-time status.
If the end-user proceeds, then the copy of the model in memory will cease to have run-time status. In order to reduce the risk of overwriting the original run-time model, the Editor will prompt for a new name if the model is subsequently saved.
Modifiable models
If you are confident that an end-user is familiar with STEM, then it may be appropriate to unlock the power of the Editor by selecting Editor Access = Modifiable, so that any assumptions in a run-time model can be changed directly without revoking the model’s run-time status.
When the exported model is first loaded into the Editor, the words ‘Original Run-Time’ will appear after the model name in the main Editor window caption, as shown below.
Modifying the assumptions will not alter the run-time status of the model; but the first time an end-user alters the value of an input, the word ‘Original’ will be removed from the caption in order to draw attention to the fact that the model may no longer contain the same assumptions as those exported by the originator.
Again, the Editor will prompt for a new name if the model is subsequently saved, in order to reduce the risk of overwriting the original run-time model.
Note: The run-time status of even a modifiable model will be revoked if the end-user creates, renames or deletes a model element, thus ensuring that the structure of the model remains fixed.
Password protection
If you have the slightest concern that a copy of a run-time model could be distributed further than you intended, or if you are simply concerned to limit access to an appropriately skilled group of individuals within an organisation, then you can set a password in the Export Run-Time Model dialog. On export, the Editor will verify this password by asking you to re-type it.
The Editor will then prompt for this password whenever an end-user attempts to load the run-time model; and will only load the model if the correct password is supplied.
Note: This password only restricts Editor access and is not required when running a model via the STEM add-in for Microsoft Excel.