Presentation on Domain Modelling Submitted by WWW ASSIGNMENTPOINT

Presentation on Domain Modelling Submitted by WWW. ASSIGNMENTPOINT. COM www. assignmentpoint. com

Domain Models A domain model is a visual representation of conceptual classes or real-world objects in a domain of interest. Identifying a rich set of objects or conceptual classes is at the heart of object-oriented analysis In domain model no operations are defined. It may show Domain objects or conceptual classes Associations between conceptual classes Attributes of conceptual classes www. assignmentpoint. com

Domain Model, a Visual Dictionary of Abstractions www. assignmentpoint. com

Domain Models are not Models of Software Components Domain model shows conceptual class, not software class www. assignmentpoint. com

Domain Models and Decomposition In structured analysis the dimension of decomposition is by processes or functions. In OO analysis the division is by conceptual classes or objects. Example conceptual classes in the Sale Domain www. assignmentpoint. com

Conceptual Classes 1. A conceptual class is an idea, thing or object. 2. It may be considered in terms of its symbol, intension and extension www. assignmentpoint. com

Conceptual Class Identification In incremental model iteratively identify classes rather than identify all classes at the beginning. For example, if the iteration is limited to cash-only Process. Sale scenario, then create domain model only for this one It is better to overspecify a domain model with lots of finegrained conceptual classes than to underspecify it. www. assignmentpoint. com

Strategies to Identify Conceptual Classes Use a conceptual class category list Identify noun phrases, though need some art Main Success Scenario (or Basic Flow): 1. Customer arrives at the POS checkout with goods and/or services to purchase 2. Cashier starts a new sale 3. Cashier enters item identifier 4. ………… www. assignmentpoint. com

Conceptual Class Category List Conceptual Class Category Examples Physical or tangible objects Register, Airplane Places Store, Airport Transactions Sale, Payment, Reservation Organizations Sales. Department, Object. Airline Rules and policies Refund. Policy, Cancellation. Policy Things in a container Item, Passenger …… ……. Table 10. 1 Conceptual Class Category List www. assignmentpoint. com

Candidate Conceptual Classes for the Sales Domain, an Example Manage r Register Cashier Paymen t Item Store Product. Catalog Sale Customer Product. Specificatio n There is no such thing as a “correct” list. It is somewhat arbitrary collection of abstractions. www. assignmentpoint. com

On Naming and Modeling Things: The Mapmaker Make a domain model in the spirit of a cartographer or mapmaker User the existing names in the territory Example, use “Borrower” or “Patron” for customer in library domain Exclude irrelevant features Pen and Paper. Bag may be excluded from sales domain Do not add things that are not there www. assignmentpoint. com

A Common Mistake in Identifying Conceptual Classes If we do not think of some conceptual class X as a number or text in the real world, X is probably a conceptual class, not an attribute. Example: Should Store be an attribute of Sale, or a separate object Should destination be an attribute of Flight, or Airport be a separate object www. assignmentpoint. com

Resolving Similar Conceptual Classes Register vs. POST (point-of-sale terminal) A domain model is not absolutely correct or wrong, but more or less useful; it is www. assignmentpoint. com a tool of communication

Specification or Description Conceptual Classes Worse Better Assume that, Item instance represents a physical item in a store; An item has a description, price, item. ID which are not recorded any-where else. Every time a real physical item is sold, the corresponding www. assignmentpoint. com Item instance is deleted from “software land”

Another Specification Example Let an airline company suffers a fatal crash of one of its planes Consequently cancels all flights for investigation, delete Flight instances, no longer a record of what flight routes the airline has www. assignmentpoint. com

Descriptions of Services Flight example is about a service rather than a good (such as a veggieburger item) Descriptions of services or service plans are commonly needed Another example: A mobile company sells difference packages such as “bronze”, “gold”, “dijuce”, “nababi call rate” etc. So you need a description class separate from an actual sold package. www. assignmentpoint. com

Modeling the Unreal World Some software system has little analogy in real world e. g. software for telecommunications. Still you can create a domain model. Messag e Connectio n Route Protocol Port www. assignmentpoint. com Dialog

UML Notations, Models and Methods: Multiple Perspectives class Domain concepts / conceptual class www. assignmentpoint. com Software / design class Implementation class e. g. Java Class

Lowering the Representational Gap www. assignmentpoint. com

Domain Modeling Guidelines List the objects using category list and noun phrase identification technique Draw them in a domain model Add associations necessary to record relationships Add attributes in necessary www. assignmentpoint. com

Domain Model: Adding Associations www. assignmentpoint. com

Associations An association is a relationship between types (or more specifically instances of those types) that indicated some meaningful and interesting connection. www. assignmentpoint. com

Criteria for Useful Associations Knowledge of a relationship that needs to be preserved for some duration – may milliseconds or years, depending on context. These are known as “need-to-know” associations. Example: Do we need to remember Sales. Line. Item instances for Sale instance. Example: Relationship between Sale and Manager? If n different objects then n*(n-1) associations. Be parsimonious. Associations derived from the Common Association List www. assignmentpoint. com

UML Association Notation www. assignmentpoint. com

Finding Associations – Common Association List Category A is a physical part of B A is a logical part of B A is a description for B A is a member of B Examples Drawer – Register Wing – Airplane Sales. Line. Item – Sale Flight. Description – Flight Cashier – Store Pilot – Airline A communicates with B Customer – Cashier A is owned by B Plane – Airline ……. . Table 11. 1 Common Association …………. www. assignmentpoint. com List

Roles Each end of an association is called a role. Roles may optionally have: Name (will discuss latter) Multiplicity Expression Navigability (will discuss latter) www. assignmentpoint. com

Multiple Associations Two types may have multiple associations www. assignmentpoint. com

Naming Associations Type. Name – Verb. Phrase – Type. Name format where the verb phrase creates a sequence that is readable and meaningful in the model context Should start with a capital letter Two common and equally legal formats for a compound association name are: Paid-by Paid. By www. assignmentpoint. com

How Detail Should Association Be? Finding conceptual classes is more important than finding association. The majority of time spent in domain model creation should be devoted to identifying conceptual classes, not associations. www. assignmentpoint. com

Next. Gen POS Domain Model www. assignmentpoint. com

Suggestions Focus on need-to-know associations Avoid redundant or derivable associations www. assignmentpoint. com

Domain Model: Adding Attributes www. assignmentpoint. com

Attributes An attribute is a logical data value of an object Keep attributes simple E. g. Boolean, Date, Number, String, Time Other examples are Address, Color, Universal Product Code (UPC) etc. Relate conceptual classes with an association, not with an attribute www. assignmentpoint. com

Examples www. assignmentpoint. com

Non-primitive Data Type Classes Represent as non-primitive class if If composed of separate sections Phone number, name of person There are operations usually associated with it, such as parsing / validation Social security number It has other attributes Promotional price could have start date and end date It is a quantity with a unit Payment amount has a unit of currency It is an abstraction of one or more types with some of these qualities www. assignmentpoint. com Item identifier may be UPC or EAN (European Article Number)

Where to Illustrate Data Type Classes? A domain model is a tool of communication; choices about what is shown should be made with that consideration in mind. www. assignmentpoint. com

Design Creep: No Attributes as Foreign Keys Relate objects with an association, not with an attribute www. assignmentpoint. com

Modeling Attribute Quantities and Units Most numeric quantities should not be represented as plain numbers. Consider price or velocity that are associated with units. www. assignmentpoint. com

Multiplicity From Sales. Line. Item to Item Derived attribute indicated with a “/” symbol www. assignmentpoint. com

Domain Model Conclusion Next. Gen POS System Model www. assignmentpoint. com