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Bonsai

Each of us would have encountered decision trees and rule engines of various kinds in our software journeys. Rule engines are typically structured as a set of rules that are evaluated against a Context. Bonsai is a data structure that models such engines as a tree of knots and edges. The kicker here is that the tree can be recursively nested, allowing you to represent really complex rules as simple nested forest of trees.

What is Bonsai?

Bonsai is a decision forest. It is Java Library for data selection based on conditions. It enables you to:

  1. Create a forest of trees with key-to-data mappings
  2. Build complex decision trees with conditional branching
  3. Represent nested, hierarchical rule structures
  4. Evaluate rules against a context to traverse the tree and select the right data element. The Context and Rules are represented by a combination of JsonPath and Query-DSL
  5. Modify trees dynamically with delta operations
  6. Maintain versioning of tree components
  7. Plug any storage implementations

Why Bonsai?

While there are several rule engine options out there, none bridge the gap between data selection and rule definition in a nice way. They are either too heavy or are workflow systems being termed as rule engines.

Consider a scenario where data elements are configurations, and different variations of these configurations are to be selected based on a set of conditions. What started off as a small rule engine for Frontend App configurations, Bonsai as a library powers a large number of use-cases internally in PhonePe. It is either used directly as a light-weight library, or wrapped in a service that provides a UI to create and manage trees. One such prominent service is an internal feature flagging and configuration system, which powers the page structure, and launch / placement of most widgets on the PhonePe app.

Visual Representation

Bonsai Representation

Note

The above image is just a manually created representation, not to be confused with any UI kit, this library does not come with one.

License

Bonsai is licensed under the Apache License 2.0. See the LICENSE file for details.