In this topic I present the original schemes prepared for the book MQL5 Programming for Traders, Part 7. They have been reworked for the book by MQ's designers, but Visio's plain rendering may probably seem more readable for someone.
Diagram of links between structures by fields with identifiers from Basic concepts of the calendar
Scheme for indexing data by hashing from Transferring calendar database to tester
ORM, Object-Relational Mapping from OOP (MQL5) and SQL integration: ORM concept
ORM Class Diagram (MQL5<->SQL) from Examples of CRUD operations in SQLite via ORM objects
Communication-component diagram of an MQL program with libraries from Development and linking binary format libraries
Structure and life cycle of the project from Projects
WebSocket class diagram from WebSocket protocol in MQL5
Scheme of interaction between an MQL program and an OpenCL attachment from Built-in support for parallel computing: OpenCL