Tuan 4 • Buoi 2 — Mo hinh hoa du lieu: ERD & Data Dictionary

Mo hinh hoa du lieu la gi va tai sao quan trong?

Sau khi hieu quy trinh (ai lam gi), BA con phai hieu du lieu (he thong luu tru cai gi, luu the nao). Mo hinh hoa du lieu giup:

• Khong sot truong du lieu trong requirement
• Phat hien mau thuan giua cac he thong (Customer ID ben A khac Customer ID ben B)
• Giao tiep ro voi developer khi thiet ke CSDL
• Lam nen tang cho API spec, data migration, bao cao

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Entity, Attribute, Relationship

Entity (Thuc the)

Mot "vat the" co y nghia nghiep vu ma he thong can luu tru. Thuong la danh tu so nhieu:

• Don_hang (Order), Khach_hang (Customer), San_pham (Product), Nhan_vien (Employee)

Attribute (Thuoc tinh)

Cac thong tin mo ta mot Entity:

• Don_hang: ma_don_hang, ngay_dat, tong_tien, trang_thai
• Khach_hang: ma_khach, ho_ten, email, so_dien_thoai, dia_chi

Primary Key (PK): thuoc tinh dinh danh duy nhat (ma_don_hang, ma_khach) Foreign Key (FK): thuoc tinh tham chieu sang entity khac (ma_khach trong Don_hang)

Relationship (Moi quan he)

Mo ta cach cac entity lien ket voi nhau:

• Don_hang dat boi Khach_hang
• Don_hang chua nhieu San_pham
• Nhan_vien xu ly nhieu Don_hang

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Cardinality (Luc luong quan he)

Luu y N-N: khi gap quan he N-N, can tao bang trung gian (junction table):

• Don_hang x San_pham → bang Don_hang_San_pham (chua ma_don, ma_sp, so_luong, don_gia)

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ERD cho he thong dat hang online (vi du Shopee)

erDiagram
    KHACH_HANG {
        int ma_khach PK
        string ho_ten
        string email
        string so_dien_thoai
        string dia_chi
    }
    DON_HANG {
        int ma_don PK
        int ma_khach FK
        date ngay_dat
        decimal tong_tien
        string trang_thai
    }
    SAN_PHAM {
        int ma_sp PK
        string ten_sp
        decimal gia
        int so_luong_ton
        int ma_danh_muc FK
    }
    DON_HANG_CHI_TIET {
        int ma_don FK
        int ma_sp FK
        int so_luong
        decimal don_gia
    }
    DANH_MUC {
        int ma_danh_muc PK
        string ten_danh_muc
    }
    KHACH_HANG ||--o{ DON_HANG : "dat"
    DON_HANG ||--|{ DON_HANG_CHI_TIET : "gom"
    SAN_PHAM ||--|{ DON_HANG_CHI_TIET : "co mat trong"
    DANH_MUC ||--o{ SAN_PHAM : "phan loai"

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Data Dictionary (Tu dien du lieu)

ERD cho ta ban do, nhung Data Dictionary cho ta chieu sau. No ghi lai chinh xac moi truong du lieu:

Data Dictionary dung de:

• Chinh dinh nghia cho developer khi code validation
• Nen tang viet test case cho QA
• Giai quyet tranh chap nghi nghia (field ngay_dat la ngay tao hay ngay giao?)

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CRUD Matrix

CRUD Matrix cho biet ai (vai tro nao) duoc lam gi (Create/Read/Update/Delete) voi du lieu nao (entity nao):

CRUD Matrix giup BA:

• Phat hien thieu permission: 'Ai cap nhat trang thai don hang?'
• Input cho Access Control / Authorization requirement
• Nen tang viet User Story: 'As a [vai tro], I can [hanh dong CRUD] [entity]'

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Tu luyen

• Cho tinh huong: He thong quan ly nhan su (HR) tai cong ty 200 nguoi. Xac dinh it nhat 4 entity chinh va ve ERD voi cardinality dung.
• Viet Data Dictionary cho entity Nhan_vien voi 6 truong — neu ro kieu du lieu, rang buoc, mo ta.
• Xay dung CRUD Matrix cho cac vai tro: Nhan_vien, Truong_phong, HR_Staff, Admin.
• Tim mot truong hop N-N trong he thong HR, de xuat bang trung gian phu hop.