# Build Event Log (BEL)
Purpose: Store build events and define views summarizing databuild application state, like partition catalog, build
status summary, job run statistics, etc.

## Architecture
- Uses [event sourcing](https://martinfowler.com/eaaDev/EventSourcing.html) / 
  [CQRS](https://www.wikipedia.org/wiki/cqrs) philosophy.
- BEL uses only two types of tables:
  - The root event table, with event ID, timestamp, message, event type, and ID fields for related event types.
  - Type-specific event tables (e.g. task even, partition event, build request event, etc).
- This makes it easy to support multiple backends (SQLite, postgres, and delta tables are supported initially).
- Exposes an access layer that mediates writes, and which exposes entity-specific repositories for reads.

## Correctness Strategy
- Access layer will evaluate events requested to be written, returning an error if the event is not a correct next. 
  state based on the involved component's governing state diagram.
- Events are versioned, with each versions' schemas stored in [`databuild.proto`](../databuild/databuild.proto).

## Write Interface
See [trait definition](../databuild/event_log/mod.rs).

## Read Repositories
There are repositories for the following entities:
- Builds
- Jobs
- Partitions
- Tasks

Generally the following verbs are available for each:
- Show
- List
- Cancel