Domain Model

Dzenan Ridjanovic

2009-03-08

Domain Model

Domain model is a semantic network of concepts and their relationships in a certain domain.

Example of a domain: Education.Example of a model: PersonalLibrary.Example of concepts: Book, Person.Example of a relationship: a person may borrow several books; a book may be lent to a person.

Model Concept

A concept often represents an organization, a product, a service, a person, a transaction, a thing, an event, ...

A concept may have many entities in a real world.

Book is a concept. There may be many books that share the same attributes.

Concept Descriptors

A concept has structure (properties, neighbors) and behavior (methods).

A concept may have an identifier.

An identifier gives a unique identity to each entity of the same concept.

Book Concept

Book properties: title, author.

Book neighbor: person.

Book identifier: title.

Book methods: isCataloged, isAvailable, checkOutTo, checkIn, catalog, discard.

Person Concept

Person properties: firstName, lastName, maxNumberOfBooks.

Person neighbor: books.

Person identifier: firstName, lastName.

Person methods: isMember, isWithoutBooks, register, unregister.

Concept Property

A property is a characteristic of its concept.

A property of an entity may be null.

A property of an entity usually carries a single value.

A property value comes from a type of possible values.

Book Property

Book property: title.

The title property is a characteristic of the Book concept.

A book must have a title.

A title of a book carries a text value.

A title text comes from String values.

Person Property

Person property: maxNumberOfBooks.

A maxNumberOfBooks is a characteristic of the Person concept.

A person may have a default value for maxNumberOfBooks.

A maxNumberOfBooks of a person carries an integer value.

Concept Neighbor

A neighbor is a relationship characteristic of its concept.

A neighbor of an entity usually references a single entity (parent neighbor) or a collection of entities (child neighbor).

A parent neighbor of an entity may be optional (null).

A child neighbor may be an empty collection of entities.

Book Neighbor

Book neighbor: person.

The person neighbor is a relationship characteristic of the Book concept.

A book may not be related to a person and in that case is available.

A book that references a person is not available.

Person Neighbor

Person neighbor: books.

The books neighbor is a relationship characteristic of the Person concept.

A person may have an empty collection of books.

Entry Concepts

Some concepts in a model are declared as entry points to the model.

Non-entry concepts are reachable only from entry concepts by following neighbors.

Concepts with only child neighbors are good candidates for entry points.

Personal Library Entries

Person

Book

Personal Library Model

Eclipse Project

Eclipse project in the modelibra space at Assembla: modelibra.beginner

src: source code

test: test code

mm: model files

Java Packages

One package for model.

One package for concepts (for a small model).

One package per concept (for larger models).

Java Classes

One class for model.

Two classes for each concept: Concept, Concepts.

Model Class

Create entry points in the model's constructor.

Concept Class

First do Concept classes for entry points.

Model parent property, properties for parent concepts, properties for child concepts.

Create child entities in the concepts's constructor.

Private set methods (or not at all) for setting parents or children.

Public attach and detach methods for relationships.

Concepts Class

Add an entity.

Get an entity based on its identifier.

Select and order methods.