mapleFU opened a new issue, #126:
URL: https://github.com/apache/iceberg-cpp/issues/126
Iceberg [1] and iceberg-rust [2] both have expression system. There are some
design trade-off:
## Bind
Both iceberg and iceberg-rust have concept of "bind". I guess this concept
is from database query compiler. Specifically, it means bind the reference ( we
name it as "term" later ) from "name" to a iceberg `Schema` with
`case_sensitive` setting.
In the iceberg java and iceberg-rust's code, the expression itself doesn't
need to Bind from expr naming to a specific structure.
## Term
In Java's implementation, `Term` has the derivation below:
```
interface Term;
interface Unbound {
Bounded Bind(Schema, caseSensitive);
NamedReference<?> ref();
}
class UnboundTerm : Term, Unbound;
class BoundedTerm : Term;
class NamedReference : UnboundTerm;
class UnbounedTransform : UnboundTerm;
class UnbounedExtract : UnboundTerm;
class BoundReference : BoundTerm;
class BounedTransform : BoundTerm;
class BounedExtract : BoundTerm;
```
The rust also has bind and Transform, but it uses different way to handle
this:
```
type Term = UnboundedTerm;
```
Instead, it uses `InclusiveProjection` to convert the `PartitionSpec` to a
expression, rules may like [3][4]:
1. Create `InclusiveProjection`
2. Each `Transform` has a `project` method, with project the partition
expression to the normal expression, and return a `Predicate` ( unbounded
filter )
## Reference
In java and rust, `Reference` implements use similiar way:
1. `Unbounded` has a "name"
2. `Bounded` is has `(name, accessor, ..)`
The accessor of `Schema` is like "index of vector".
## Expression
Expression itself doesn't have any bind logic, it just bind all subfields
## Evaluator
TBD
[1]
https://github.com/apache/iceberg/tree/e5541de0fd1e850f188ff89cac1417b3ae3500a4/api/src/main/java/org/apache/iceberg/expressions
[2]
https://github.com/apache/iceberg-rust/tree/f1e79c0d9c76e90cb4ceb1f2c409ef8d1b68b273/crates/iceberg/src/expr
[3]
https://github.com/apache/iceberg-rust/blob/f1e79c0d9c76e90cb4ceb1f2c409ef8d1b68b273/crates/iceberg/src/expr/visitors/inclusive_projection.rs#L85
[4]
https://github.com/apache/iceberg-rust/blob/f1e79c0d9c76e90cb4ceb1f2c409ef8d1b68b273/crates/iceberg/src/spec/transform.rs#L471
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