You are a seasoned backend architect with 10+ years of experience building scalable and reliable systems.  A new startup, &#8220;InnovateTech,&#8221; is developing a SaaS application for managing project workflows. They need a robust backend system capable of handling a projected 10,000 concurrent users within the first year.  Their current technical stack includes Node.js, PostgreSQL, and Redis.  They require a detailed plan outlining the backend logic, including data modeling, API design, database schema, and crucial considerations for scalability and security.  Your task is to create this plan, addressing the following: </p>
<p>**I. Data Modeling:** Define the core entities (e.g., users, projects, tasks, teams) and their relationships.  Include attributes for each entity and specify data types. Consider normalization and potential future scalability needs.</p>
<p>**II. API Design:** Design RESTful APIs to handle CRUD operations for each entity.  Specify endpoints, HTTP methods, request/response structures (using JSON), and error handling strategies.  Consider API versioning and authentication/authorization mechanisms.</p>
<p>**III. Database Schema:**  Translate the data model into a detailed PostgreSQL schema, including table definitions, indexes, and foreign keys.  Explain your choices regarding data types and indexing strategies.</p>
<p>**IV. Scalability and Security:**  Outline strategies for ensuring scalability (e.g., load balancing, caching, database sharding) and security (e.g., input validation, authentication, authorization, data encryption).  Justify your recommendations.</p>
<p>**V. Technology Choices:**  Explain your reasoning behind using Node.js, PostgreSQL, and Redis for this project.  Would you recommend any additional technologies or libraries to enhance performance or functionality?  Justify your choices.</p>
<p>Deliver your plan as a structured document with clear headings and subheadings.  Use bullet points and concise language where appropriate.  Prioritize clarity and practicality.  Your plan should be sufficient for a development team to begin implementing the backend system.