Import node pre processing

Status

Discsusion

Proposed by: Adam Gibson (11-25-2021)

Discussed with: Paul Dubs

Context

Nd4j's model import framework supports different protobuf based frameworks for importing and executing models. This was introduced in 0003-Import_IR.md One problem with importing models is compatibility between different versions of frameworks. Often,migrations are needed to handle compatibility between versions. A node pre processor is proposed that: when combined with the model import framework allows for annotation based automatic upgrades of graphs.

Decision

In order to handle preprocessing a node to handle things like upgrades. An end user can specify a pre processor via a combination of 2 interfaces:

An annotation for specifying a class that implements a relevant rule for processing. This will automatically be discoverable via annotation scanning similar to other frameworks. This annotation looks as follows:

annotation class NodePreProcessor(val nodeTypes: Array<String>, val frameworkName: String)

The information include the nodeTypes which are the operation types to scan for when doing upgrades on a graph. The framework name: relevant if multiple import modules are on the classpath. Filters rules by their intended framework for import.

The necessary pre processing hook that will handle processing the node and may modify the graph. Graph modification maybe necessary if we need to add new nodes to compensate for modification of a node such as an attribute moving to being an input.


interface NodePreProcessorHook<NODE_TYPE : GeneratedMessageV3,
        TENSOR_TYPE : GeneratedMessageV3,
        ATTRIBUTE_TYPE : GeneratedMessageV3,
        ATTRIBUTE_VALUE_TYPE : GeneratedMessageV3, DATA_TYPE>
        where  DATA_TYPE: ProtocolMessageEnum {


            fun modifyNode(
                node: IRNode<NODE_TYPE, TENSOR_TYPE, ATTRIBUTE_TYPE, ATTRIBUTE_VALUE_TYPE, DATA_TYPE>,
                graph: IRGraph<GeneratedMessageV3, GeneratedMessageV3, GeneratedMessageV3, GeneratedMessageV3, GeneratedMessageV3, GeneratedMessageV3, ProtocolMessageEnum>
            ): IRNode<NODE_TYPE, TENSOR_TYPE, ATTRIBUTE_TYPE, ATTRIBUTE_VALUE_TYPE, DATA_TYPE>

}

Discussion

Consequences

Advantages

An automatic way of extending support for model import by providing users a hook mechanism for handling graph modification
Extends the model import process to handle nodes in an op specific way allowing a way of handling op specific interactions simplifying maintenance of other aspects of the import framework

Disadvantages

Adds a 3rd kind of hook for model import, thus more for users to learn
Can be difficult to implement if user doesn't know how to work with graphs
May have unforeseen consequences of testing due to graph modification after creation

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