Domain Modelling

Domain model is a UML model that is drawn to understand the important objects and their business context.

A domain is a collection of related concepts, relationships, and workflows.

Eg : Science ,  Software engineering , Statistics  

Why Domain Model?

ü  Gives a conceptual framework of the things in the problem space

ü  Helps you think – focus on semantics

ü  Provides a glossary of terms – noun based

ü  It is a static view - meaning it allows us convey time invariant business rules

ü  Foundation for use case/workflow modelling

ü  Based on the defined structure, we can describe the state of the problem domain at any time.

Figure 1 : Usage of a Domain Model

Parts of a Domain Model

The Figure 2 Shows the main parts of a Domain model.

Figure 2 : Parts of a Domain Model

Apart from these key features, a domain model can also have,

o        Additional rules – complex rules that cannot be shown with symbology can be shown with attached notes.

 

Figure 3 : Sample Domain Model

Wanna try out a domain model?? 

 Follow these steps (figure 4)…..

Figure 4 : Domain Modelling Steps

Concentrate more on just identifying domain classes in early steps !

Identify the domain classes?

An obvious way to identify domain classes is to identify nouns and phrases in textual descriptions of a domain.

Consider a use case description as follows:-

1.      Customer arrives at a checkout with goods and/or services to purchase.

2.      Cashier starts a new sale.

3.      Cashier enters item identifier.

      4.      System records the sale line item and presents the item  description, price and running total. 

Identifying Attributes??

A domain class sounds like an attribute if: -

1.       It relies on an associated class for it’s identity – e.g. ‘order number’ class associated to an ‘order’ class. The ‘order number’ sounds suspiciously like an attribute of ‘order’.

2.       It is a simple data type – e.g. ‘order number’ is a simple integer. Now it really sounds like an attribute!