Low-level design (LLD) for an inventory management system:

1. Product catalog: The system will need to store information about the products in the inventory, such as the product name, SKU, description, and current quantity. This will likely involve creating a database or data structure to store this information.

2. Order processing: The system will need to allow users to place orders for products and update the inventory accordingly. This will involve creating forms and handling the associated server-side logic to process the orders and update the inventory.

3. Stock management: The system will need to track the current stock levels and alert users when the stock is running low or has run out. This will involve implementing logic to monitor the inventory and generate alerts when necessary.

4. Reporting and analytics: The system will need to provide reports and analytics on the inventory, such as sales data and product popularity. This will involve implementing functions to query and analyze the data, as well as creating views to display the results.

5. User accounts and authentication: The system will need to allow users to create accounts, log in, and log out. We will also need to implement measures to ensure the security of user accounts, such as password hashing and potentially two-factor authentication.

6. User interface: Finally, the system will need to design the user interface for the service, including the layout, navigation, and any necessary graphics or styling. This will involve creating wireframes and mockups, as well as implementing the front-end code to bring the design to life.

Here is a possible low-level design for an inventory management system in Java:

public class Product {
    private long id;
    private String name;
    private String description;
    private double price;
    private int quantity;

    public Product(String name, String description, double price, int quantity) {
        this.id = IdGenerator.generateId();
        this.name = name;
        this.description = description;
        this.price = price;
        this.quantity = quantity;
    }

    public long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getDescription() {
        return description;
    }

    public double getPrice() {
        return price;
    }

    public int getQuantity() {
        return quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
}

public class Order {
    private long id;
    private Customer customer;
    private Map<Product, Integer> products;
    private LocalDateTime createdAt;
    private OrderStatus status;

    public Order(Customer customer, Map<Product, Integer> products, LocalDateTime createdAt) {
        this.id = IdGenerator.generateId();
        this.customer = customer;
        this.products = products;
        this.createdAt = createdAt;
        this.status = OrderStatus.PENDING;
    }

    public long getId() {
        return id;
    }

    public Customer getCustomer() {
        return customer;
    }

    public Map<Product, Integer> getProducts() {
        return products;
    }

    public LocalDateTime getCreatedAt() {
        return createdAt;
    }

    public OrderStatus getStatus() {
        return status;
    }

    public void setStatus(OrderStatus status) {
        this.status = status;
    }
}

public enum OrderStatus {
    PENDING,
    PROCESSING,
    SHIPPED,
    DELIVERED,
    CANCELLED
}

public class Customer {
    private long id;
    private String name;
    private String email;
    private String phone;
    private String address;

    public Customer(String name, String email, String phone, String address) {
        this.id = IdGenerator.generateId();
        this.name = name;
        this.email = email;
        this.phone = phone;
        this.address = address;
    }

    public long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    public String getPhone() {
        return phone;
    }

    public String getAddress() {
        return address;
    }
}

public class InventoryManagementSystem {
    private Map<Long, Product> products;
    private Map<Long, Order> orders;
    private Map<Long, Customer> customers;

    public InventoryManagementSystem() {
        this.products = new HashMap<>();
        this.orders = new HashMap<>();
        this.customers = new HashMap<>();
    }

    public void addProduct(Product product) {
        products.put(product.getId(), product);
    }

    public Product getProduct(long id) {
        return products.get(id);
    }

    public void updateProductQuantity(long productId, int quantity) {
        Product product = products.get(productId);
        if (product != null) {
            product.setQuantity(quantity);
        }
    }

    public void placeOrder(Order order) {
        orders.put(order.getId(), order);
    }

    public Order getOrder(long id) {
        return orders.get(id);
    }

    public void updateOrderStatus(long orderId, OrderStatus status) {
        Order order = orders.get(orderId);
        if (order != null) {
            order.setStatus(status);
        }
    }

    public void addCustomer(Customer customer) {
        customers.put(customer.getId(), customer);
    }

    public Customer getCustomer(long id) {
        return customers.get(id);
    }
}