[GitHub] [arrow] westonpace commented on a change in pull request #10934: [RFC] Arrow Compute Serialized Intermediate Representation draft for discussion

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westonpace commented on a change in pull request #10934:
URL: https://github.com/apache/arrow/pull/10934#discussion_r698867003



##########
File path: format/experimental/computeir/Expression.fbs
##########
@@ -0,0 +1,351 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+include "../../Schema.fbs";
+include "Literal.fbs";
+include "InlineBuffer.fbs";
+
+namespace org.apache.arrow.computeir.flatbuf;
+
+/// Access a value for a given map key
+table MapKey {
+  key: string (required);
+}
+
+/// Struct field access
+table StructField {
+  /// The position of the field in the struct schema
+  position: uint32;
+}
+
+/// Zero-based array index
+table ArraySubscript {
+  position: uint32;
+}
+
+/// Zero-based range of elements in an array
+table ArraySlice {
+  /// The start of an array slice, inclusive
+  start_inclusive: uint32;
+  /// The end of an array slice, exclusive
+  end_exclusive: uint32;
+}
+
+/// Field name in a relation
+table FieldName {
+  position: uint32;
+}
+
+/// A union of possible dereference operations
+union Deref {
+  /// Access a value for a given map key
+  MapKey,
+  /// Access the value at a struct field
+  StructField,
+  /// Access the element at a given index in an array
+  ArraySubscript,
+  /// Access a range of elements in an array
+  ArraySlice,
+  /// Access a field of a relation
+  FieldName,
+}
+
+/// Access the data of a field
+table FieldRef {
+  /// A sequence of field names to allow referencing potentially nested fields
+  ref: Deref (required);
+  /// For Expressions which might reference fields in multiple Relations,
+  /// this index may be provided to indicate which Relation's fields
+  /// `path` points into. For example in the case of a join,
+  /// 0 refers to the left relation and 1 to the right relation.
+  relation_index: int;
+}
+
+/// A canonical (probably SQL equivalent) function
+//
+// TODO: variadics
+enum CanonicalFunctionId : uint32 {
+  // logical
+  And,
+  Not,
+  Or,
+
+  // arithmetic
+  Add,
+  Subtract,
+  Multiply,
+  Divide,
+  Power,
+  AbsoluteValue,
+  Negate,
+  Sign,
+
+  // date/time/timestamp operations
+  DateSub,
+  DateAdd,
+  DateDiff,
+  TimeAdd,
+  TimeSub,
+  TimeDiff,
+  TimestampAdd,
+  TimestampSub,
+  TimestampDiff,
+
+  // comparison
+  Equals,
+  NotEquals,
+  Greater,
+  GreaterEqual,
+  Less,
+  LessEqual,
+}
+
+table CanonicalFunction {
+  id: CanonicalFunctionId;
+}
+
+table NonCanonicalFunction {
+  name_space: string;
+  name: string (required);
+}
+
+union FunctionImpl {
+  CanonicalFunction,
+  NonCanonicalFunction,
+}
+
+/// A function call expression
+table Call {
+  /// The kind of function call this is.
+  kind: FunctionImpl (required);
+
+  /// The arguments passed to `function_name`.
+  arguments: [Expression] (required);
+
+  /// Parameters for `function_name`; content/format may be unique to each
+  /// value of `function_name`.
+  metadata: InlineBuffer;
+}
+
+/// A single WHEN x THEN y fragment.
+table CaseFragment {
+  when: Expression (required);
+  then: Expression (required);
+}
+
+/// Case statement-style expression.
+table Case {
+  cases: [CaseFragment] (required);
+  /// The default value if no cases match. This is typically NULL in SQL
+  //implementations.
+  ///
+  /// Defaulting to NULL is a frontend choice, so producers must specify NULL
+  /// if that's their desired behavior.
+  default: Expression (required);
+
+  /// Parameters for `function_name`; content/format may be unique to each
+  /// value of `function_name`.
+  metadata: InlineBuffer;
+}
+
+table Cast {
+  /// The expression to cast
+  expression: Expression (required);
+
+  /// The type to cast `argument` to.
+  type: org.apache.arrow.flatbuf.Field (required);
+
+  /// Parameters for `function_name`; content/format may be unique to each
+  /// value of `function_name`.
+  metadata: InlineBuffer;
+}
+
+table Extract {
+  /// Expression from which to extract components.
+  expression: Expression (required);
+
+  /// Field to extract from `expression`.
+  field: string (required);
+
+  /// Parameters for `function_name`; content/format may be unique to each
+  /// value of `function_name`.
+  metadata: InlineBuffer;
+}
+
+/// Whether lesser values should precede greater or vice versa,
+/// also whether nulls should preced or follow values.
+enum Ordering : uint8 {
+  ASCENDING_THEN_NULLS,
+  DESCENDING_THEN_NULLS,
+  NULLS_THEN_ASCENDING,
+  NULLS_THEN_DESCENDING
+}
+
+/// An expression with an order
+table SortKey {
+  expression: Expression (required);
+  ordering: Ordering = ASCENDING_THEN_NULLS;
+}
+
+/// Boundary is unbounded
+table Unbounded {}
+
+union ConcreteBoundImpl {
+  Expression,
+  Unbounded,
+}
+
+/// Boundary is preceding rows, determined by the contained expression
+table Preceding {
+  ipml: ConcreteBoundImpl (required);
+}
+
+/// Boundary is following rows, determined by the contained expression
+table Following {
+  impl: ConcreteBoundImpl (required);
+}
+
+/// Boundary is the current row
+table CurrentRow {}
+
+union BoundImpl {
+  Preceding,
+  Following,
+  CurrentRow,
+}
+
+/// Boundary of a window
+table Bound {
+  impl: BoundImpl (required);
+}
+
+/// The kind of window function to be executed.
+enum Frame : uint8 {
+  Rows,
+  Range,
+}
+
+/// An expression representing a window function call.
+table WindowCall {
+  /// The kind of window frame
+  kind: Frame;
+  /// The expression to operate over
+  expression: Expression (required);
+  /// Partition keys
+  partitions: [Expression] (required);
+  /// Sort keys
+  orderings: [SortKey] (required);
+  /// Lower window bound
+  lower_bound: Bound (required);
+  /// Upper window bound
+  upper_bound: Bound (required);
+}
+
+/// A canonical (probably SQL equivalent) function
+enum CanonicalAggregateId : uint32 {
+  All,
+  Any,
+  Count,
+  CountTable,
+  Mean,
+  Min,
+  Max,
+  Product,
+  Sum,
+  Variance,
+  StandardDev,
+}
+
+
+table CanonicalAggregate {
+  id: CanonicalAggregateId;
+}
+
+table NonCanonicalAggregate {
+  name_space: string;
+  name: string (required);
+}
+
+union AggregateImpl {
+  CanonicalAggregate,
+  NonCanonicalAggregate,
+}
+
+table AggregateCall {
+  /// The kind of aggregate function being executed
+  kind: AggregateImpl (required);
+
+  /// Aggregate expression arguments
+  arguments: [Expression] (required);
+
+  /// Possible ordering.
+  orderings: [SortKey];
+
+  /// optional per-aggregate filtering
+  predicate: Expression;
+}
+
+/// An expression is one of
+/// - a Literal datum
+/// - a reference to a field from a Relation
+/// - a call to a named function
+/// - a case expression
+/// - a cast expression
+/// - an extract operation
+/// - a window function call
+/// - an aggregate function call
+///
+/// The expressions here that look like function calls such as
+/// Cast,Case and Extract are special in that while they might
+/// fit into a Call, they don't cleanly do so without having
+/// to pass around non-expression arguments as metadata.
+///
+/// AggregateCall and WindowCall are also separate variants
+/// due to special options for each that don't apply to generic
+/// function calls. Again this is done to make it easier
+/// for consumers to deal with the structure of the operation
+union ExpressionImpl {
+  Literal,
+  FieldRef,
+  Call,
+  Case,
+  Cast,
+  Extract,
+  WindowCall,
+  AggregateCall,
+}
+
+/// Expression types
+///
+/// Expressions have a concrete `impl` value, which is a specific operation
+/// They also have a `type` field, which is the output type of the expression,
+/// regardless of operation type.
+///
+/// The only exception so far is Cast, which has a type as input argument, which
+/// is equal to output type.
+table Expression {
+  impl: ExpressionImpl (required);
+
+  /// The type of the expression.
+  ///
+  /// This is a field, because the Type union in Schema.fbs
+  /// isn't self-contained: Fields are necessary to describe complex types
+  /// and there's currently no reason to optimize the storage of this.
+  type: org.apache.arrow.flatbuf.Field;

Review comment:
       Please take this with the usual caveat that I am no expert in this field.
   
   > A producer and a consumer that are not self-contained. This is the broadest use case and I think will be the primary way in which the IR is used. In this scenario, the producer inserts a type into this field as the output of its type system. The consumer is then required to adhere to what the producer asked for, or return an error.
   
   This sounds like the user needs to create overloads based solely on the return type.  I feel like that will be rare enough that it can be handled via the name or the call arguments/options.  For example, `add_unchecked(int32, int32) => int32` and `add_or_widen(int32, int32) => int64`.  It would be odd for me to pick which behavior I get by specifying the return type.
   
   > A producer and consumer that are self-contained. This is for a system such as a relational database (e.g., DuckDB), where the IR is being used by a system that controls both the producer and the consumer. The purpose of the type field here is to have a place for the output of a type derivation step to be stored after its derivation for later consumption.
   
   This feels like a slippery slope.  Wouldn't it be better for DuckDB in this case to extend the fbs with their own fields?
   
   




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