SSM files with no mapping entries causes crash during instantiation

[AxelMatstoms]

Description

Empty SSM files seem to cause OMS to bypass some of the logic that normally allows values in SSV files with no corresponding parameters in the system.

Steps to reproduce the behavior

SSP file demonstrating issue. In this case we have an SSV file with some parameters with no corresponding parameter in the system.

<?xml version='1.0' encoding='utf-8'?>
<ssv:ParameterSet xmlns:ssc="http://ssp-standard.org/SSP1/SystemStructureCommon" xmlns:ssv="http://ssp-standard.org/SSP1/SystemStructureParameterValues" version="2.0" name="parameters">
  <ssv:Parameters>
    <ssv:Parameter name="t_start">
      <ssv:Real value="0.0" unit="None"/>
    </ssv:Parameter>
    <ssv:Parameter name="t_end">
      <ssv:Real value="10.0" unit="None"/>
    </ssv:Parameter>
  </ssv:Parameters>
</ssv:ParameterSet>

and an SSM file with no entries:

<?xml version='1.0' encoding='utf-8'?>
<ssm:ParameterMapping xmlns:ssc="http://ssp-standard.org/SSP1/SystemStructureCommon" xmlns:ssm="http://ssp-standard.org/SSP1/SystemStructureParameterMapping" version="2.0">
</ssm:ParameterMapping>

SSP file:
example.zip

from OMSimulator import SSP

ssp = SSP("example.ssp")

instantiated_model = ssp.instantiate()

instantiated_model.setResultFile("out.csv")
instantiated_model.setStopTime(10)
instantiated_model.setFixedStepSize(0.05)

instantiated_model.initialize()
instantiated_model.simulate()
instantiated_model.terminate()
instantiated_model.delete()

When simulating this with latest version of OMS OMSimulator v3.0.0.post164-g33c40b0-linux i get the following error:

error:   [setReal] Unknown signal "model.root.t_start"
Traceback (most recent call last):
  File "/home/axema/Documents/oms3-ssv-example/sim.py", line 5, in <module>
    instantiated_model = ssp.instantiate()
                         ^^^^^^^^^^^^^^^^^
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/ssp.py", line 438, in instantiate
    return self.activeVariant.instantiate(self.resources, self.temp_dir)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/ssd.py", line 273, in instantiate
    return InstantiatedModel(json_desc, self.system, resources)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/instantiated_model.py", line 253, in __init__
    self.setStartValuesFromSSV(self.system.parameterResources, self.system.name)
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/instantiated_model.py", line 291, in setStartValuesFromSSV
    self.setStartValues(ssv.value, systemName, ssm)
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/instantiated_model.py", line 370, in setStartValues
    self.apply_start_value(value_path, source_value, type)
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/instantiated_model.py", line 384, in apply_start_value
    self._setReal(value_path, float(value_))
  File "/home/axema/Documents/OMSimulator/install/lib/x86_64-linux-gnu/OMSimulator/instantiated_model.py", line 489, in _setReal
    raise RuntimeError(f"Failed to set value for {mapped_cref}: {status}")
RuntimeError: Failed to set value for model.root.t_start: Status.error
info:    0 warnings
info:    1 errors

Adding a dummy entry to the SSM file, e.g:

<ssm:ParameterMapping xmlns:ssc="http://ssp-standard.org/SSP1/SystemStructureCommon" xmlns:ssm="http://ssp-standard.org/SSP1/SystemStructureParameterMapping" version="2.0">
  <ssm:MappingEntry source="dummy" target="dummy2"/>
</ssm:ParameterMapping>

makes the SSP work again.

Expected behavior

SSP is able to be instantiated and should be able to simulate.

Version

• OMSimulator v3.0.0.post164-g33c40b0-linux
• Ubuntu 24.04

[arun3688]

@AxelMatstoms the issue is fixed with this commit 5847ede, The code is raising error for unknown signals which can be part of ssv or ssm files, right now warning is generated and continue with simulation, please test it from the master

[AxelMatstoms]

@arun3688 Jorge and I have done some additional testing on our side. I think we end up in the wrong branch inside setStartValues with an empty SSM file.

    ## apply ssm mapping if exist and apply start values from mapped parameters
    if ssm and ssm.mappingEntry:

But if there are no entries, ssm.mappingEntry is an empty defaultdict which evaluates to False. But we should use that branch whenever there is an SSM file, even if it is empty. From SSP v1.0.1 ch 7.1:

All parameters of the parameter source which are not referenced in a mapping entry will not be applied. All parameters that are referenced in a mapping entry will only be applied using the name they are mapped to, i.e. any original name is disregarded for applying parameters.

This should apply even when the SSM file is "empty", and in that case the consequence should be that nothing is mapped. Is there any reason we can't just change the condition to ssm is not None?

[arun3688]

@AxelMatstoms you are correct, we should not check for ssm.mappingEntry, we just need to check for ssm file is referenced, please feel free to change the condition as you said if ssm:

[AxelMatstoms]

I tried this approach in #1634. It was not as simple as just changing the condition. Because the condition is almost always true, because empty SSM objects are used as default values in System and Component. Currently there is no way to differentiate between the empty SSM object that was set as a default value and an empty SSM that was parsed from XML. Without a way to differentiate between these states, the first branch is always taken, meaning SSV files with names that do not require mapping never work.

Possible approaches:

• Use None as a default value. Requires lots of None checks wherever parameterMappings is accessed or modified.
• Implement a default state for SSM that indicates it does not represent an empty SSM file. For example mappingEntry = None. Some actions should set mappingEntry = defaultdict(list) if not already set: importFromSSM, mapParameter. But the user also needs a way to create an SSM object that represents an empty SSM.

[arun3688]

@AxelMatstoms i can look into it tomorrow and try to fix it

[arun3688]

@AxelMatstoms the issue is fixed with this commit 8ce1f2d, the solution was very simple than expected, check for ssm.filename for ssm files and ssm.mappingEntry for inline parameter mapping and it should handle the case of empty ssm files. please pull the latest changes from master and test it

[AxelMatstoms]

@arun3688 Nice! We've tested the latest commit from master, and your solution works well for our use-case. Thanks!