Facing issues when Tensorflow model involves a String as input/output to serving function

[chaitanya-basava]

Hi,
I am testing out a tensorflow model which takes a string as input and returns the spell corrected version of this string and it's confidence score. The signature_def retuned for the model using saved_model_cli is as following

signature_def['serving_default']:
  The given SavedModel SignatureDef contains the following input(s):
    inputs['query'] tensor_info:
        dtype: DT_STRING
        shape: (-1)
        name: serving_default_query:0
  The given SavedModel SignatureDef contains the following output(s):
    outputs['corrected_query'] tensor_info:
        dtype: DT_STRING
        shape: ()
        name: StatefulPartitionedCall_5:0
    outputs['score'] tensor_info:
        dtype: DT_DOUBLE
        shape: unknown_rank
        name: StatefulPartitionedCall_5:1
  Method name is: tensorflow/serving/predict

But when loading the model on DJL, the loaded model is only identifying score as model output. corrected_query is not getting returned when checking with model.describeOutput().keys() and only score is getting returned upon model prediction call.

Any support or document around solving this issue would be really helpful.

Thanks

[frankfliu]

@chaitanya-basava

This is current limitation in DJL. We filtered out String tensor in the output (https://github.com/deepjavalibrary/djl/blob/master/engines/tensorflow/tensorflow-engine/src/main/java/ai/djl/tensorflow/engine/TfSymbolBlock.java#L120). Since we added String Tensor support, should be able to add String tensor support. Can you share your model or point to a similar model, so we can add a test for this type of model.

[chaitanya-basava]

@frankfliu thanks for the response. I won't be able to share the exact model file, so have created this dummy model which has similar input and output signatures, except it would be returning the query string as corrected_query and score=0.0

model.zip

Hope this will be helpful.

Wanted to clarify one more thing would there be a similar behaviour (of string output's getting filtered out) when using other model types like onnx and pytorch as well?

[frankfliu]

@chaitanya-basava

You can try nightly snapshot build once this PR is merged.
The ONNX and PyTorch engine should not have this issue. This tensorflow behavior is more like a bug (we forget to remove this limit when we added String tensor support).