## ADDED Requirements
### Requirement: Abstract Base Dataset Handler
An abstract base class `BaseDatasetHandler` SHALL be created to define common interface and shared implementations for dataset operations.

#### Scenario: Base class provides common functionality
- **GIVEN** both PyArrow and DuckDB backends inherit from BaseDatasetHandler
- **WHEN** common operations are called on either backend
- **THEN** shared implementations SHALL be used automatically
- **AND** backend-specific operations SHALL be properly delegated

### Requirement: Shared Merge Utilities
Common merge logic SHALL be extracted into shared utilities in `fsspeckit.core.merge` module.

#### Scenario: Eliminated code duplication
- **GIVEN** merge operations in both PyArrow and DuckDB backends
- **WHEN** code is examined after refactoring
- **THEN** duplicate merge logic SHALL be removed from individual backends
- **AND** both backends SHALL use shared utilities from core.merge

### Requirement: Shared Compaction and Optimization
Common compaction and optimization logic SHALL be extracted into shared functions.

#### Scenario: Reusable maintenance operations
- **GIVEN** compaction and optimization operations in both backends
- **WHEN** these operations are performed
- **THEN** shared implementations SHALL handle the common logic
- **AND** backend-specific optimizations SHALL be applied as needed

## MODIFIED Requirements
### Requirement: Backend Implementation Structure
Backend-specific implementations SHALL inherit from base class and only override necessary methods.

#### Scenario: Cleaner backend implementations
- **GIVEN** PyArrow and DuckDB backend classes
- **WHEN** implementation structure is examined
- **THEN** both backends SHALL inherit from BaseDatasetHandler
- **AND** only backend-specific methods SHALL be overridden
- **AND** common functionality SHALL use inherited implementations

## REMOVED Requirements
### Requirement: Duplicate Implementation Code
Duplicate code between PyArrow and DuckDB backends SHALL be eliminated.

#### Scenario: No code duplication
- **GIVEN** the refactored codebase
- **WHEN** similar functionality is searched across backends
- **THEN** no significant duplicate code SHALL exist
- **AND** all shared functionality SHALL use common utilities
