Day 4 Summary Codex AI Architect Technical Design

Day 4. Technical design (API design and interface definition) training summary

It contains key summary information on the state-of-the-art interface collaboration architecture that creates an API Contract, which is a promise to connect planning and development, based on the requirements definition and screen definition, identifies inconsistencies and missing items between each document, and automates analysis and testing of UI and API dependency impacts due to changes.

Part 1. Introduction background
Part 2. Practice objectives
Part 3. Follow along
Part 4. How it works
Part 5. Training Guide
Part 6. Final Task

Bottleneck in technical design

Errors in understanding between planning, design, and development at the project site directly lead to database omission and loss of consistency. Find out why ensuring consistency at the design stage is important.

understanding error

Because the fields of the planning document or screen design and the actually distributed API spec are different, communication errors or defects in which certain values ​​do not appear on the screen occur one after another.

vocabulary error

Fields are defined and developed only through verbal agreements between front-end and back-end developers, but the names (Camel vs. Snake Case) and format do not match, so the meeting is repeated every time.

shared error

Even if a single business requirement, such as price or order stage, changes, a huge analysis cost is incurred to check the scope of modifications to the API, front screen, and test code connected to it.

ChatGPT vs Codex Client (Workspace-based)

Unlike ChatGPT, which is limited to a single conversation context, we compare the characteristics of Codex Client, which recognizes the entire folder structure and dependency relationships between multiple files.

Compare items ChatGPT (General Conversational AI) Codex Client (Workspace-based AI)
Context awareness Cross-verification of actual field mapping and functional compliance between plan, screen design, and backend API specification file By tracking the properties of multiple outputs from planning-screen-API, three-dimensional detection of ratings, missing error codes, etc.
API mismatch detection Only roughly configures a one-time API code template Self-recommendation of consistent standard naming and DB column names based on project standard terminology dictionary
Scope of Impact Analysis Level of suggestions for fragmentary schema errors or hypothetical table modifications Reverse inference on list of API specifications and screen modification areas according to subtle changes in schema (e.g. column addition)

Summary of final results to be created today

A list of the final products the learner produces during the Day 4 session and the purpose of those products.

Task 01. Data structuring

Entities and relationships are extracted and rendered from the natural language plan. Mermaid ERD scripts and statements (Output: erd-schema.md)

Task 02. API mismatch detection

Fragmented Korean/English planning terms defined in standard English column format Project Standards Glossary (Output: project-glossary.md)

Task 03. Analysis of API change impact

API and screen modification list according to addition of reservation approval system (WAIT_APPROVE) Change impact analysis report (Output: change-impact-report.md)

Mission 01. Design record

Archives the reasons for normalization and data design decisions and rejected alternatives. Design Decision Log (DDL) (Output: design-decision-log.md)

Mission 02. Create API test scenario

Contains DB improvement measures for concurrent payment errors, referential integrity loss of withdrawal, and transaction rollback. Edge Case Analysis Report (Output: edge-case-analysis.md)

Input / Output data pipeline

This is a mapping between the input values used in the practice stage and the results generated through Codex Workspace inference.

01
data structure
02
Terminology standardization
03
Impact of change
M1
decision making
M2
Exception scenario
Task 01. Create API contract
πŸ“₯ Input (planning meeting minutes)
β€’ day4_meeting_notes.md (meeting minutes) - User flow scenario and reservation process content in the form of irregular lines
Codex Workspace βž”
πŸ’Ύ Output (ERD specification)
erd-schema.md with Mermaid ERD code - Visualization of Primary Key/Foreign Key relationships of User, Expert, Reservation, and Payment entities

STEP 1. Task 01 - Create API contract

Enter meeting scenario lines to derive precise normalization relationships (1:N, 1:1) and Mermaid codes.

πŸ” Codex request prompt (data structuring)

Based on the provided requirements definition and screen definition, please derive a list of required APIs and create a standard API contract by defining the types of Request and Response fields and English variable names.
  • Check whether the PK and FK settings of the four major entities, User, Expert, Reservation, and Payment, do not conflict with the scenario logic.
  • When rendering a Mermaid diagram (`erDiagram`), check that the cardinality notation is correct.

STEP 2. Task 02 - API mismatch detection

We build a master dictionary of domain terms by comparing and analyzing the gap between Figma planning terms and DB development specifications.

πŸ” Codex request prompt (generating a glossary of terms)

Please cross-check the provided day4_requirements.md, day4_screen_definition.md, and day4_api_specification_v1.md files to find any API endpoints and fields that are inconsistent or missing from the planning requirements or screen UI design and create a review report.
  • Check whether the English standard naming and column type information that matches the business domain are presented correctly.

STEP 3. Task 03 - Analysis of API change impact

Understand the scope of API and table impact when a release plan change adds an 'Approval' step to the scheduling process.

πŸ” Codex request prompt (understand scope of influence)

Analyze the contents of the provided API change request (day4_api_change_request.md) to derive a list of other system areas and documents affected when modifying the reservation request API, and prepare an API impact analysis that can be immediately shared with team members.
  • Check whether status changes in the Reservations table, new API specifications, and button state transition chain effects on the planning screen have been detected.

STEP 4. Mission 01 - API review and improvement (Design Decision Log)

Log rejection reasons and agreements regarding normalization decisions, physical separation decisions for reservation history, etc.

πŸ” Codex request prompt (decision record)

Please review the provided API specification of day4_api_specification_v1.md, analyze improvements based on REST API design standards (HTTP Method usage, URL naming), consistent error handling structure, and extensibility, and write an API review report.
  • Check whether the background of the decision to separate history tables (DEC-003) and the alternatives (performance degradation when unifying tables) are clearly logged.

STEP 5. Mission 02 - Create an API test scenario (Edge Case)

We audit system vulnerabilities to prevent referential integrity violations (withdrawals) and transaction collapses.

πŸ” Codex request prompt (Edge case derivation)

Based on the currently defined reservation and payment API specifications, please create an API test scenario and verification checklist that includes both the normal registration flow (Happy Path) and exception cases such as missing required parameters, date format errors, limit exceeded, and permission expiration.
  • Check the plan to maintain reference consistency and distributed transaction rollback response by introducing soft delete (logical deletion).

How it works and its core mechanisms

Schema context-aware reasoning

Beyond simple text matching, it identifies the referential integrity (FK) relationships and transaction life cycle of entities and automatically deduces natural language proposals into Data Definition Language (DDL) queries and state machine rules.

Meta term clustering

We derive a master dictionary of enterprise terms by semantically clustering differently written terms (customer name vs. nickname), and synchronize the consistency of the data dictionary based on this.

Technical design synergy of five Tasks/Missions

We check how the data and analysis information derived from each step goes through the technical design loop to maximize quality.

[API interface contract] (Task 01. Derive specifications)
β–Ό
[Planning-API discrepancy verification] (Task 02. Consistency audit)
β–Ό
[Automatic tracking of design change aftermath] (Task 03. Impact management)
β–Ό
[Improvement of REST architecture quality] (Mission 01. Structure review)
β–Ό
[Happy/Sad Path Test Coverage] (Mission 02. Scenario Defense)

This interface verification pipeline removes all errors and design inconsistencies before writing a single line of code, ensuring high-quality interface so that the front and backend can successfully build integration at once.

πŸ’‘ Educational design specifications

  • Difficulty level: β˜…β˜…β˜…β˜…β˜† (Advanced - includes database design normalization and distributed transaction concepts)
  • Estimated lab time: 1 hour 30 minutes ~ 2 hours (comprehensive design practice)
  • Practical usability: β˜…β˜…β˜…β˜…β˜…

Learner questions/discussion topics

This is a list of topics that are great for discussion during training or to use as interview questions.

Q1. Membership Withdrawal Strategy

β€œWhen an error occurs, what are the pros and cons from a microservice architecture (MSA) perspective between the custom error of unconditionally sending the HTTP Status as 200 OK and displaying a detailed error code in the body (Custom Error) and using the HTTP standard Status (4xx, 5xx)?”

Q2. Terminology Debt

β€œWhen a project progresses to mid-way without creating an API mismatch detection dictionary, how does the β€˜terminology debt’ cost incurred within the development team affect the actual schedule?”

Planning and design stage final training task

This is a diagram of the overall practice tasks and missions covered on Day 4.

Task topic How to use AI
Task 01 Create an API contract Automatically derive RESTful API contract specifications by analyzing the plan and screen design
Task 02 API mismatch detection Automatically detects discrepancies (missing ratings, etc.) between planning specifications and API specifications and generates reports
Task 03 API change impact analysis Track chain effects of screens and specifications that need to be linked when API parameters or status change
Mission 01 API reviews and improvements API Review Report that standardizes noun URLs, error code exception schemas, etc. to come up with improvement plans
Mission 02 Create an API test scenario Derive an exception test matrix that responds to missing essential keys and format errors as well as normal operation flow
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