{
  "format": "entitymodeler",
  "format_version": 1,
  "source": "https://entitymodel.com",
  "name": "library_management",
  "title": "Library Management System",
  "organization": "EntityModel.com examples",
  "description": "A library: books and authors (many-to-many), physical copies at branches, members, loans, holds and fines.",
  "version": "1.0",
  "author": "EntityModel.com",
  "status": "approved",
  "created_at": "2026-11-03T00:00:00.000Z",
  "updated_at": "2026-11-03T00:00:00.000Z",
  "entities": [
    {
      "name": "book",
      "display_name": "Book",
      "entity_type": "standard",
      "color_code": "#3E6A8F",
      "description": "A title in the catalog. Physical copies are separate.",
      "attributes": [
        {
          "name": "book_id",
          "label": "Book ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "4410"
        },
        {
          "name": "isbn",
          "label": "ISBN",
          "type": "STRING",
          "required": true,
          "unique": true,
          "description": "ISBN-13.",
          "example": "9780262033848"
        },
        {
          "name": "title",
          "label": "Title",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "Introduction to Algorithms"
        },
        {
          "name": "publisher_id",
          "label": "Publisher ID",
          "type": "INT",
          "example": "17"
        },
        {
          "name": "publication_year",
          "label": "Publication Year",
          "type": "INT",
          "example": "2009"
        },
        {
          "name": "language_code",
          "label": "Language Code",
          "type": "REFERENCE_ENTITY",
          "reference": {
            "entity": "language",
            "output_attribute": "language_code"
          },
          "required": true,
          "example": "en"
        },
        {
          "name": "genre_code",
          "label": "Genre Code",
          "type": "REFERENCE_ENTITY",
          "reference": {
            "entity": "genre",
            "output_attribute": "genre_code"
          },
          "example": "CS"
        }
      ],
      "struct_types": [],
      "area": "Catalog"
    },
    {
      "name": "author",
      "display_name": "Author",
      "entity_type": "standard",
      "color_code": "#7A5C8E",
      "description": "A person who wrote or edited books.",
      "attributes": [
        {
          "name": "author_id",
          "label": "Author ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "210"
        },
        {
          "name": "author_name",
          "label": "Author Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "Thomas H. Cormen"
        },
        {
          "name": "birth_year",
          "label": "Birth Year",
          "type": "INT",
          "example": "1956"
        }
      ],
      "struct_types": [],
      "area": "Catalog"
    },
    {
      "name": "publisher",
      "display_name": "Publisher",
      "entity_type": "standard",
      "color_code": "#1F6366",
      "description": "A publishing house.",
      "attributes": [
        {
          "name": "publisher_id",
          "label": "Publisher ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "17"
        },
        {
          "name": "publisher_name",
          "label": "Publisher Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "MIT Press"
        }
      ],
      "struct_types": [],
      "area": "Catalog"
    },
    {
      "name": "library_branch",
      "display_name": "Branch",
      "entity_type": "standard",
      "color_code": "#9A4A10",
      "description": "A library location that holds copies.",
      "attributes": [
        {
          "name": "branch_id",
          "label": "Branch ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "3"
        },
        {
          "name": "branch_name",
          "label": "Branch Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "Central Library"
        },
        {
          "name": "address",
          "label": "Address",
          "type": "STRING",
          "required": true,
          "example": "801 SW 10th Ave"
        },
        {
          "name": "phone",
          "label": "Phone",
          "type": "STRING",
          "example": "+1 555 0170"
        }
      ],
      "struct_types": [],
      "area": "Lending"
    },
    {
      "name": "book_copy",
      "display_name": "Copy",
      "entity_type": "standard",
      "color_code": "#4A4D52",
      "description": "A physical copy of a book, with its own barcode, kept at one branch.",
      "attributes": [
        {
          "name": "copy_id",
          "label": "Copy ID",
          "type": "BIGINT",
          "is_primary_key": true,
          "required": true,
          "example": "1004410"
        },
        {
          "name": "barcode",
          "label": "Barcode",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "unique": true,
          "example": "31234001004410"
        },
        {
          "name": "book_id",
          "label": "Book ID",
          "type": "INT",
          "required": true,
          "example": "4410"
        },
        {
          "name": "branch_id",
          "label": "Branch ID",
          "type": "INT",
          "required": true,
          "example": "3"
        },
        {
          "name": "condition",
          "label": "Condition",
          "type": "STRING",
          "example": "Good"
        },
        {
          "name": "is_available",
          "label": "Is Available",
          "type": "BOOLEAN",
          "required": true,
          "description": "Not on loan or held.",
          "example": "true"
        }
      ],
      "struct_types": [],
      "area": "Lending"
    },
    {
      "name": "member",
      "display_name": "Member",
      "entity_type": "standard",
      "color_code": "#2F5D73",
      "description": "A person with a library card.",
      "attributes": [
        {
          "name": "member_id",
          "label": "Member ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "56002"
        },
        {
          "name": "card_number",
          "label": "Card Number",
          "type": "STRING",
          "required": true,
          "unique": true,
          "pii": true,
          "example": "2900156002"
        },
        {
          "name": "full_name",
          "label": "Full Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "pii": true,
          "example": "Lee Chen"
        },
        {
          "name": "email",
          "label": "Email",
          "type": "STRING",
          "pii": true,
          "example": "lee.chen@example.com"
        },
        {
          "name": "membership_type_code",
          "label": "Membership Type Code",
          "type": "REFERENCE_ENTITY",
          "reference": {
            "entity": "membership_type",
            "output_attribute": "type_code"
          },
          "required": true,
          "example": "ADULT"
        },
        {
          "name": "joined_on",
          "label": "Joined On",
          "type": "DATE",
          "required": true,
          "example": "2024-06-11"
        },
        {
          "name": "expires_on",
          "label": "Expires On",
          "type": "DATE",
          "required": true,
          "example": "2027-06-11"
        }
      ],
      "struct_types": [],
      "area": "Lending"
    },
    {
      "name": "loan",
      "display_name": "Loan",
      "entity_type": "standard",
      "color_code": "#5C7F9E",
      "description": "A copy checked out to a member.",
      "attributes": [
        {
          "name": "loan_id",
          "label": "Loan ID",
          "type": "BIGINT",
          "is_primary_key": true,
          "required": true,
          "example": "902211"
        },
        {
          "name": "copy_id",
          "label": "Copy ID",
          "type": "BIGINT",
          "required": true,
          "example": "1004410"
        },
        {
          "name": "member_id",
          "label": "Member ID",
          "type": "INT",
          "required": true,
          "example": "56002"
        },
        {
          "name": "loaned_on",
          "label": "Loaned On",
          "type": "DATE",
          "is_label": true,
          "required": true,
          "example": "2026-10-20"
        },
        {
          "name": "due_on",
          "label": "Due On",
          "type": "DATE",
          "required": true,
          "example": "2026-11-10"
        },
        {
          "name": "returned_on",
          "label": "Returned On",
          "type": "DATE",
          "description": "Empty while on loan."
        },
        {
          "name": "renewal_count",
          "label": "Renewal Count",
          "type": "INT",
          "required": true,
          "example": "0"
        }
      ],
      "struct_types": [],
      "area": "Lending"
    },
    {
      "name": "hold",
      "display_name": "Hold",
      "entity_type": "standard",
      "color_code": "#A12F18",
      "description": "A member's request to borrow a book when a copy becomes available.",
      "attributes": [
        {
          "name": "hold_id",
          "label": "Hold ID",
          "type": "BIGINT",
          "is_primary_key": true,
          "required": true,
          "example": "33019"
        },
        {
          "name": "book_id",
          "label": "Book ID",
          "type": "INT",
          "required": true,
          "example": "4410"
        },
        {
          "name": "member_id",
          "label": "Member ID",
          "type": "INT",
          "required": true,
          "example": "56002"
        },
        {
          "name": "pickup_branch_id",
          "label": "Pickup Branch ID",
          "type": "INT",
          "required": true,
          "example": "3"
        },
        {
          "name": "placed_at",
          "label": "Placed At",
          "type": "TIMESTAMP",
          "is_label": true,
          "required": true,
          "example": "2026-10-28T12:00:00Z"
        },
        {
          "name": "status",
          "label": "Status",
          "type": "STRING",
          "required": true,
          "description": "Waiting, ready, fulfilled or cancelled.",
          "example": "WAITING"
        }
      ],
      "struct_types": [],
      "area": "Lending"
    },
    {
      "name": "fine",
      "display_name": "Fine",
      "entity_type": "standard",
      "color_code": "#3E6A8F",
      "description": "A charge for a late or lost item.",
      "attributes": [
        {
          "name": "fine_id",
          "label": "Fine ID",
          "type": "BIGINT",
          "is_primary_key": true,
          "required": true,
          "example": "7701"
        },
        {
          "name": "loan_id",
          "label": "Loan ID",
          "type": "BIGINT",
          "required": true,
          "example": "902211"
        },
        {
          "name": "amount",
          "label": "Amount",
          "type": "DECIMAL",
          "precision": 12,
          "scale": 2,
          "is_label": true,
          "required": true,
          "example": "2.50"
        },
        {
          "name": "reason",
          "label": "Reason",
          "type": "STRING",
          "required": true,
          "example": "Overdue"
        },
        {
          "name": "paid_on",
          "label": "Paid On",
          "type": "DATE"
        }
      ],
      "struct_types": [],
      "area": "Lending"
    },
    {
      "name": "book_author",
      "display_name": "Book Author",
      "entity_type": "standard",
      "color_code": "#7A5C8E",
      "description": "Links books to their authors, in credit order.",
      "attributes": [
        {
          "name": "book_id",
          "label": "Book ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "4410"
        },
        {
          "name": "author_id",
          "label": "Author ID",
          "type": "INT",
          "is_primary_key": true,
          "required": true,
          "example": "210"
        },
        {
          "name": "author_order",
          "label": "Author Order",
          "type": "INT",
          "is_label": true,
          "required": true,
          "description": "Position in the author list.",
          "example": "1"
        }
      ],
      "struct_types": [],
      "area": "Catalog"
    },
    {
      "name": "genre",
      "display_name": "Genre",
      "entity_type": "reference",
      "color_code": "#4E7C8C",
      "description": "Subject classification for books.",
      "attributes": [
        {
          "name": "genre_code",
          "label": "Genre Code",
          "type": "STRING",
          "is_primary_key": true,
          "required": true,
          "example": "CS"
        },
        {
          "name": "genre_name",
          "label": "Genre Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "Computer science"
        }
      ],
      "struct_types": [],
      "reference_values": [
        {
          "genre_code": "FIC",
          "genre_name": "Fiction"
        },
        {
          "genre_code": "MYS",
          "genre_name": "Mystery"
        },
        {
          "genre_code": "SCI",
          "genre_name": "Science"
        },
        {
          "genre_code": "CS",
          "genre_name": "Computer science"
        },
        {
          "genre_code": "HIST",
          "genre_name": "History"
        },
        {
          "genre_code": "CHILD",
          "genre_name": "Children"
        }
      ],
      "reference_values_source": "Example values"
    },
    {
      "name": "language",
      "display_name": "Language",
      "entity_type": "reference",
      "color_code": "#4E7C8C",
      "description": "Languages, by ISO 639-1 code.",
      "attributes": [
        {
          "name": "language_code",
          "label": "Language Code",
          "type": "STRING",
          "is_primary_key": true,
          "required": true,
          "example": "en"
        },
        {
          "name": "language_name",
          "label": "Language Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "English"
        }
      ],
      "struct_types": [],
      "reference_values": [
        {
          "language_code": "en",
          "language_name": "English"
        },
        {
          "language_code": "es",
          "language_name": "Spanish"
        },
        {
          "language_code": "fr",
          "language_name": "French"
        },
        {
          "language_code": "de",
          "language_name": "German"
        },
        {
          "language_code": "zh",
          "language_name": "Chinese"
        }
      ],
      "reference_values_source": "ISO 639-1 (excerpt)"
    },
    {
      "name": "membership_type",
      "display_name": "Membership Type",
      "entity_type": "reference",
      "color_code": "#4E7C8C",
      "description": "Kinds of library card, with their loan limits.",
      "attributes": [
        {
          "name": "type_code",
          "label": "Type Code",
          "type": "STRING",
          "is_primary_key": true,
          "required": true,
          "example": "ADULT"
        },
        {
          "name": "type_name",
          "label": "Type Name",
          "type": "STRING",
          "is_label": true,
          "required": true,
          "example": "Adult"
        },
        {
          "name": "max_loans",
          "label": "Max Loans",
          "type": "INT",
          "required": true,
          "example": "20"
        }
      ],
      "struct_types": [],
      "reference_values": [
        {
          "type_code": "ADULT",
          "type_name": "Adult",
          "max_loans": "20"
        },
        {
          "type_code": "CHILD",
          "type_name": "Child",
          "max_loans": "10"
        },
        {
          "type_code": "STUDENT",
          "type_name": "Student",
          "max_loans": "25"
        },
        {
          "type_code": "SENIOR",
          "type_name": "Senior",
          "max_loans": "20"
        }
      ],
      "reference_values_source": "Example values"
    }
  ],
  "relationships": [
    {
      "name": "published_by",
      "source": "book",
      "target": "publisher",
      "cardinality": "N:1",
      "forward_label": "Published By",
      "reverse_label": "Publishes",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "publisher_id"
    },
    {
      "name": "credits_book",
      "source": "book_author",
      "target": "book",
      "cardinality": "N:1",
      "forward_label": "Credits",
      "reverse_label": "Credited In",
      "bidirectional": true,
      "description": "Books and authors are many-to-many; book_author resolves it and keeps the credit order.",
      "attributes": [],
      "foreign_key": "book_id"
    },
    {
      "name": "credits_author",
      "source": "book_author",
      "target": "author",
      "cardinality": "N:1",
      "forward_label": "Credits",
      "reverse_label": "Credited In",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "author_id"
    },
    {
      "name": "copy_of",
      "source": "book_copy",
      "target": "book",
      "cardinality": "N:1",
      "forward_label": "Copy Of",
      "reverse_label": "Has Copy",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "book_id"
    },
    {
      "name": "kept_at",
      "source": "book_copy",
      "target": "library_branch",
      "cardinality": "N:1",
      "forward_label": "Kept At",
      "reverse_label": "Holds",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "branch_id"
    },
    {
      "name": "loan_of",
      "source": "loan",
      "target": "book_copy",
      "cardinality": "N:1",
      "forward_label": "Of",
      "reverse_label": "Loaned In",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "copy_id"
    },
    {
      "name": "borrowed_by",
      "source": "loan",
      "target": "member",
      "cardinality": "N:1",
      "forward_label": "Borrowed By",
      "reverse_label": "Borrows",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "member_id"
    },
    {
      "name": "hold_on",
      "source": "hold",
      "target": "book",
      "cardinality": "N:1",
      "forward_label": "On",
      "reverse_label": "Has Hold",
      "bidirectional": true,
      "description": "Holds are on the title, not a specific copy.",
      "attributes": [],
      "foreign_key": "book_id"
    },
    {
      "name": "placed_by",
      "source": "hold",
      "target": "member",
      "cardinality": "N:1",
      "forward_label": "Placed By",
      "reverse_label": "Places",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "member_id"
    },
    {
      "name": "pickup_at",
      "source": "hold",
      "target": "library_branch",
      "cardinality": "N:1",
      "forward_label": "Pick Up At",
      "reverse_label": "Pickup Point For",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "pickup_branch_id"
    },
    {
      "name": "charged_for",
      "source": "fine",
      "target": "loan",
      "cardinality": "N:1",
      "forward_label": "Charged For",
      "reverse_label": "Incurs",
      "bidirectional": true,
      "description": "",
      "attributes": [],
      "foreign_key": "loan_id"
    }
  ],
  "hierarchies": [],
  "areas": [],
  "notes": []
}