--- title: "Domain modeling; attributes and associations guidelines" subject: "Object Oriented Analysis and Design" chapter: 2 key: "semester_6/object_oriented_analysis_and_design:domain-modeling-attributes-associations" source: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/domain-modeling-attributes-associations site: BCT Engineering --- # Domain modeling; attributes and associations guidelines Object Oriented Analysis and Design · Chapter 2: Object Oriented Analysis - Asked in: 2072 Asoj, 6 marks - Video: [Domain Modeling Crash Course](https://www.youtube.com/watch?v=bduWjKNrnAg) — Tobias Olsson - Page: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/domain-modeling-attributes-associations - Whole chapter: https://www.bctengineer.com/md/semester_6/object_oriented_analysis_and_design/chapter-2 ## Question What do you mean by Domain Modeling? Present the guidelines to add attributes and associations in the domain model. ## Short answer Domain model is a visual representation of conceptual classes, attributes, and associations of the problem domain (no operations). Attributes: use simple data types, no foreign keys, model quantity with units, avoid derived values unless marked /. Associations: add only needed relationships, name association, show multiplicity, avoid redundant ones. ## Answer #### Domain modeling A **domain model** (conceptual class model) is a visual representation of the **conceptual classes** or real-situation objects of the problem domain: the important concepts, their attributes and their relationships. It is the main artifact of OOA. It is drawn as a UML class diagram **without operations**, and it is a "visual dictionary" of the domain's vocabulary. It describes the real world, not software classes. ```text +--------+ 1 * +--------+ 1 1..* +---------+ | Member |-------| Loan |----------| Book | +--------+ makes +--------+ of +---------+ | name | | date | | title | +--------+ +--------+ | isbn | +---------+ ``` #### Guidelines to add attributes 1. Include attributes that the requirements suggest or imply a need to remember information (e.g. receipt needs date and time). 2. Use **simple data types** (number, text, date, boolean) for attributes. Relate to other classes with **associations**, not attributes. (Do not make `customerId` in `Sale`; relate `Sale` to `Customer`.) 3. Do not use attributes as **foreign keys**. 4. Model quantities with their units, using a class (`Quantity`, `Money`) when needed. 5. Keep data-type classes (address, phone) as attributes if they are simple; make them classes if they have structure or rules. 6. Do not add attributes whose value can be calculated (derived), unless marked `/`. 7. Keep the model small: add only attributes that matter for the current iteration. #### Guidelines to add associations 1. Add associations for relationships the system needs to **remember** for some time (need-to-know). 2. Add associations from the **Common Association List**: A is a physical/logical part of B; A is a description of B; A is contained in B; A uses or manages B; A is owned by B; A is a member of B; A is transaction related to B (Customer-Payment); A is next to B; A is a transaction/event recorded in B. 3. Name an association as `ClassName-VerbPhrase-ClassName`, readable in one direction. 4. Show **multiplicity** at both ends. 5. Avoid too many associations, and omit those that can be derived from others (redundant). 6. Use role names where the same class takes part in different ways. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a domain model? A. A diagram of software classes with all operations B. A database schema C. A visual representation of conceptual classes of the real problem domain, without operations D. A deployment diagram Answer: C. It is a UML class diagram without operations showing real-world concepts, attributes and relationships. (Key point: Domain model definition) 2. Which attribute guideline is correct? A. Use customerId in Sale as a foreign key B. Relate classes with associations, not foreign-key attributes C. Always add derived attributes D. Add every possible attribute Answer: B. Sale should be associated with Customer rather than storing a customerId attribute. (Key point: No foreign keys) 3. How should an association be named? A. Any random word B. No name is ever needed C. With a noun only D. ClassName-VerbPhrase-ClassName, readable in one direction Answer: D. A verb-phrase name such as Member makes Loan reads naturally in one direction. (Key point: Association naming) 4. Which associations should be added? A. Those the system needs to remember for some time (need-to-know) or from the common association list B. All possible associations C. Only derived or redundant ones D. None, only attributes Answer: A. Add need-to-know associations and avoid too many or redundant ones. 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