--- title: "Point of sale class diagram" subject: "Object Oriented Analysis and Design" chapter: 2 key: "semester_6/object_oriented_analysis_and_design:pos-class-diagram-multiplicity" source: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/pos-class-diagram-multiplicity site: BCT Engineering --- # Point of sale class diagram Object Oriented Analysis and Design · Chapter 2: Object Oriented Analysis - Asked in: 2069 Poush, 6 marks - Video: [UML class diagrams](https://www.youtube.com/watch?v=6XrL5jXmTwM) — Lucid Software - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/pos-class-diagram-multiplicity - Whole chapter: https://www.bctengineer.com/md/semester_6/object_oriented_analysis_and_design/chapter-2 ## Question Draw a class diagram for point of sale system with association and multiplicity. ## Short answer A Store has 1..* Registers; each Register records many Sales. Each Sale consists of 1..* SalesLineItems pointing to a ProductSpecification. A Sale is paid by exactly 1 Payment. A Cashier handles many Sales. Composition: SalesLineItems are part of a Sale. ## Answer A **Point of Sale (POS)** system records sales and payments at a store checkout. The class diagram below is based on Larman's classic POS domain. **Assumptions:** one store with several registers; one cashier handles each sale; each sale is paid by a single (cash) payment. ```text +-------+ 1 1..* +----------+ | Store |----------| Register | +-------+ houses +----------+ | 1 | records | * +---------+ 1 * +-----------+ 1 1 +---------+ | Cashier |--------| Sale |-------| Payment | +---------+handles |-----------| paid |---------| | date,time | by | amount | | total() | +---------+ +-----------+ | 1 (composition) | 1..* +-----------+ | SalesLine | | Item | | quantity | +-----------+ | * | 1 +-----------+ | Product | Store 1 ---- * ProductSpec | Spec | (store stocks products) +-----------+ ``` #### Multiplicity table | Association | Multiplicity | Meaning | |---|---|---| | Store - Register | 1 to 1..* | A store has one or more registers | | Register - Sale | 1 to * | A register records many sales over time | | Sale - SalesLineItem | 1 to 1..* | A sale has at least one line item | | SalesLineItem - ProductSpecification | * to 1 | Many lines refer to the same product | | Sale - Payment | 1 to 1 | A sale is paid by one payment | | Cashier - Sale | 1 to * | A cashier handles many sales | | Store - ProductSpecification | 1 to * | A store stocks many products | Composition: `Sale` is composed of `SalesLineItem`s (a line item cannot exist without its sale). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the POS diagram, what is the Store to Register multiplicity? A. 1 to 1..* B. 0..1 to * C. * to 1 D. 1 to 1 Answer: A. A store houses one or more registers. (Key point: Store-Register multiplicity) 2. Sale and SalesLineItem are related as: A. Sale inherits from SalesLineItem B. Each sale has exactly one line item C. Sale composes 1..* line items; a line item cannot exist without the sale D. Line items are independent of any sale Answer: C. Composition: the part's life depends on the whole, and a sale has at least one line. (Key point: Sale-SalesLineItem) 3. Why is SalesLineItem to ProductSpecification many-to-one? A. Each product can be sold only once B. A line holds many products C. A product has many stores D. Many lines can refer to the same product Answer: D. Many line items across sales may refer to the same product specification. (Key point: SalesLineItem-ProductSpecification) 4. Under the stated assumption, Sale to Payment is: A. * to * B. 0..1 to * C. 1 to 1 D. 1 to * Answer: C. Each sale is paid by one (cash) payment. 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