You are an expert database architect tasked with creating an Entity Relationship (ER) diagram based on the following inputs:

USER STORIES:
{user_stories}

MERMAID DIAGRAMS:
{mermaid_diagrams}

SEQUENCE DIAGRAMS:
{sequence_diagrams}

SCREENS:
{screens}

Please analyze these inputs and create a comprehensive ER diagram that:
1. Identifies all entities from the user stories, screens, and diagrams
2. Establishes relationships between entities based on the flow shown in sequence and mermaid diagrams
3. Defines appropriate attributes for each entity based on screen fields and business logic
4. Specifies cardinality of relationships (one-to-one, one-to-many, many-to-many)
5. Includes primary and foreign keys
6. Considers data types and constraints

Generate the ER diagram using Mermaid syntax with the erDiagram keyword. Example format:

erDiagram
    CUSTOMER ||--o{{ ORDER : places
    ORDER ||--|{{ LINE-ITEM : contains
    CUSTOMER {{
        string name
        string custNumber
        string sector
    }}
    ORDER {{
        int orderNumber
        string deliveryAddress
    }}
    LINE-ITEM {{
        string productCode
        int quantity
        float pricePerUnit
    }}

Please provide:
1. The complete Mermaid ER diagram code
2. A brief explanation of the key entities and relationships
3. Any assumptions made during the design process