Business Modeling – The Domain Model

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Business Modeling – The Domain Model

Source: Use Case Driven Object Modeling with UML – A Practical Approach

By Doug Rosenberg ISBN: 0-201-43289-7 Also, pp. 101-110 OOSE Text

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Background

 A key component of Business Modeling (Domain Analysis) - in addition to Business Use Case Model and Business Object Model and other artifacts - is the Domain Model

 Recall the Business Model is not only a graphical model, but also other artifacts such as the Business Vision, Business Rules,

Business Glossary, Business Risk List, and the Domain Model.

 All relate to the enterprise / organization.

 The Domain Model contains Key Abstractions (business / technology)

 Is a Visual Model of business entities, relationships, multiplicities, and more.

 Prior to embarking on gathering requirements and capturing them via Use Cases (application use cases, requirements use cases, that is…), we

need to understand the key entities in the business domain.

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Domain Modeling - an Introduction

 Domain Modeling is the task of discovering “objects”

(classes, actually) that represent those business entities and concepts.

  Recognize that the domain model will be a superset of your entity classes needed for your application development.

 These class diagrams – later on - will likely contain some of the entities found in your domain model.

 These appear similar to ERDs, but they are not the same.

 Fully-attributed list (not a schema or physical database design…)

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Domain Modeling - continued

 Domain Models sometimes considered ‘informal’ class diagrams.

 Developed as part of domain analysis (business modeling)

 The ‘classes’ (entities) represent what you have learned about various ‘things’ (entities) and relationships between/among them in the business domain itself.

 As a Visual Model, this model helps in understanding the domain.

  Also serves as a Glossary, in that the entities will contain attributes and other defining qualities.

 Think ‘Customer, ’ ‘Product Line’ etc.

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Domain Modeling - continued

 The Domain Model:

 Does NOT wholly support requirements analysis (ahead).

 Is not INTENDED to…

 Addresses entities in the domain of the organization – that may be quite apart (superset) from a computer application that may use them.

 Are normally not concerned with representations of

 inheritance,

 polymorphism, etc, but can show aggregation, multiplicities, etc.

 (as we would be when embarking on development of an application.)

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Domain Modeling - continued

 In requirements analysis –

 as part of gathering information on the application to be developed,

 we develop class diagrams - contain entities (classes) taken from the domain model.

  But the class diagrams (for development) will represent data that will be stored and manipulated by the application.

  Class diagrams also include operations (methods, uses)

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Domain Modeling - continued

 Models produced as part of requirements analysis (ahead lectures) will contain:

 Entity classes –

 some may be derived from Domain Model, (Most complicated)

 Boundary classes –

 used for the user interface and external system interfaces with, perhaps, systems/ databases that already exist;

 Control Classes

 used for controlling logic and business rules, and, in general, orchestrating the application functions.

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So, what do we do?

 Doing domain modeling is very important.

 Don’t want to spend too much time trying to model everything!!!

 Yet we need to have a good starting point for requirements analysis to solve the ‘problem.’

 So, our domain modeling approach is to develop an ‘initial’ set of business entities (nouns).

 This is a a static model of the domain by finding appropriate entities that represent the real key abstractions in the domain.

 A ‘key abstraction’ example is Customer, Product, Account, etc.

 Serve to underpin system development later.

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Developing Entities for Domain Model

 Sources (again) of Domain Knowledge. Here are a few:

 Interviews

 Questionnaires

 Quarterly Reports

 Mission Statements

 Subject Matter Experts (SMEs)

 Newsletters

 Web pages

 A company’s e-business….

 Look for nouns in these sources! – these are candidate classes in the domain model.

 More examples: Menu, Customer, Food order, Payment, On-line order…Things!

 Customer (class with attributes) ‘orders’ (relationship) Food (class with attributes)

 Capture graphically!

 ‘Customer’ and ‘Food’ are entities related by ‘Orders’ with multiplicity 1..n.

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Developing Domain Entities

 Read sources very closely;

 Capture these ‘nouns’ and noun phrases.

 Look for the ‘things’ in the domain…

 Possessive phrases generally indicate that the nouns should be attributes rather than objects.

 Try to identify attributes but omit operations.

 Build associations (and name them) between domain entities

 Add multiplicities carefully

 Don’t worry about aggregations and association classes and much more unless these relationships are clearly evident.

 Model in some tool.

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Generalization Relationships and Associations

 If clear from your info gathering, build generalization relationships

 Parents, subclasses…. Inheritance of attributes, methods, and associations! Not a must, but if clear: do it.

 ‘is a’ relationships….

 Associations are static relationships between classes.

 Semantic relationships. A class may have many students…

 Show dependencies if needed.

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Associations and Multiplicity

 Label the associations as best you can (and you should)

 Try to identify multiplicities, but don’t spend too much time.

 Aggregations – identify classes such that one class is

‘made up’ from smaller pieces… ‘has a’ or ‘is a kind of’.

 You are familiar with this concept from OOP.

 Also, there is composition – where one piece is ‘owned’ by another – later…..

 Focus on simple aggregations now.

 Don’t stress on relationships not obvious at this time.

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Association Classes

 Identify classes that particularly address the

‘many-to-many’ relationships that link classes

 patient and doctor? m:n?

 These ‘associations’ typically have properties independent of classes they are linking.

 Most domain models have at least one or two link

(sometimes called ‘bridge’) classes. We really don’t care at this time…(These are implementation dependencies)

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Following slide is an example (has a few errors in it) that you may use as a guide.

8 Top Domain Modeling Errors

 8. Start assigning multiplicities to associations right off the bat. Make sure that every association has an explicit multiplicity.

 7. Undertake noun and verb analysis so exhaustively that you pass out along the way.

 6. Debate whether to use aggregation or composition for each of your part-of associations

  5. Presume a specific implementation strategy without modeling the problem space.

 4. Use hard-to-understand names for your classes – like cPortMgrIntf – instead of intuitively obvious ones, such as PortfolioManager.

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Continuing…

 3. Jump directly to implementation constructs such as ‘friend’ relationships and parameterized classes

 2. Create a one-for-one mapping between domain classes and relational database tables.

 1. Perform “premature patternization,” which involves building cool solutions, from patterns, that have little or no connection to user problems.

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Transition to:

The Problem Space!!!



Area within which your application is to

exist!

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The Problem and the Scope



The term “problem domain” refers to the area that encompasses real-world persons, places, and/or things and concepts related to the

problem that the system to be developed / enhanced, etc. is being ‘required’ to solve.



A ‘problem’ may be considered a ‘difficulty’

(inadequacy of current system) or ‘opportunity’

for benefit, or more

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Problem Statement (‘Product Vision’ - Statement of Need.)

 The problem statement should be a simple sentence or two or three.

 Usually then found in a Product Vision Document

  VERY IMPORTANT; Needs are very high level and usually include more than that which can be

accommodated by an automated system.

 Basis to answer the ultimate question:

 Have we solved the problem?

 Be careful what you write!!!

 Wild inferences can be made.

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Sample Problem Statement – Need.

(Student Registration System)



“The system will allow students to register for

courses, and change their registration, as simply and rapidly as possible. It will help students

achieve their personal goals of obtaining their degree in the shortest reasonable time while

taking courses that they find most interesting and

fulfilling.”

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Scope and Its Bounds

 Broader the scope, the more complex the application.

 Scope exists along with the problem statement

 This will narrow include a list of features.

 Features can be accommodated by an automated system.

 These can simply be ‘bulleted’ items

 Scope, hence commitment, is clarified by listing features or sub-problems.

 Determine that some of these are ‘out of scope’ or will be accommodated by a different application.

 Good to have a comprehensive list citing features that are explicitly OUT of scope as well as those IN scope.

Business Modeling – The Domain Model