Architecture

Services

Memo Service - Stores memos and accepts live streams of voice data from clients. The voice stream is then transcribed into texts. When a summary of the memos is requested, the service then sends required data to Summary Service asynchronously. Memo Service uses MongoDB as a database because it can accept data as streams.
Elastic Search - Finds memos by spoken words in recorded voices, using full-text search techniques.

We use MongoDB because it can stream data into a document which SQL db can not achieve this.